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February 8, 2002 www.xilinx.com 1 1-800-255-7778 R Tutorial Designing Custom OPB Slave Peripherals for MicroBlaze Summary This document offers recommended guidelines and practices for RTL designers to create custom OPB slave peripherals for MicroBlaze embedded systems. An introduction to On- chip Peripheral Bus (OPB) signals, basic transactions and tips for RTL coding are discussed here. Overview In an embedded system design, the peripherals (for example, timers, DMA, interrupt controller, custom applications, etc.) must be connected to the microprocessor using the data and address buses. The complexity of system-on-chip (SOC) devices makes standardizing the connection of different macro cells one of the top priorities in defining an embedded system. Xilinx MicroBlaze have implemented IBM's CoreConnect architecture. Ultimately, designing a complex chip based on existing intellectual property and design reuse methodology could become a straightforward task. On-chip Peripheral Bus (OPB) version 2.1 of CoreConnect architecture is designed for easy connection of on-chip peripheral devices. Any custom peripheral that connects to the OPB bus must meet the principles of the OPB protocol and the design must meet the requirements of Platform Generator and CoreGen flow to take advantage of the simple automated flow that generates the system-level architecture as well as other template scripts supported by Xilinx. Features Platform Generator supports the following features of on-chip peripherals and is a subset of OPB v2.1 features: • Fully synchronous single clock edge • 32-bit address bus, 32-bit data bus • Single-cycle transfer of data between OPB master and OPB slave • Supports master byte enables • Supports slave timeout suppress • Supports slave retry • No tristate drivers required Note that the dynamic bus sizing feature is not supported in OPB v2.1. Figure 1 is a block diagram of a MicroBlaze-based embedded system. 2 www.xilinx.com February 8, 2002 1-800-255-7778 Tutorial: Designing Custom OPB Slave Peripherals for MicroBlaze R An OPB peripheral of MicroBlaze can be portable to Virtex-II ProTM devices. Figure 2 is a block diagram of a Virtex-II Pro-based embedded system. Physical Implementation Figure 3 shows a simplified physical implementation of the OPB. This bus architecture allows for the addition of peripherals to the system without changing the existing I/O on either the OPB arbiter or other existing peripherals. Figure 1: MicroBlaze-Based Embedded System Figure 2: Virtex-II Pro-Based Embedded System OPB Arbiter OPB Slave (Ex: UART) OPB Slave (Ex: Interrupt Controller) OPB Slave (Ex: GPIO) OPB Master (Ex: DMA) MicroBlaze as OPB Master OPB Bus xip2043 OPB Arbiter PLB Arbiter PPC 405 Processor Block OPB Peripheral OPB Peripheral OPB Peripheral OPB Peripheral PLB-to-OPB Bridge OPB-to-PLB Bridge PLB Peripheral PLB Peripheral D_Side PLB I/F I_Side PLB I/F PLB OPB xip2044 February 8, 2002 www.xilinx.com 3 1-800-255-7778 Interface Signals R The module opb_v20 in the diagram implements the OR gates defined by the OPB v2.1 specification. Based on the Microprocessor Hardware Specification file (MHS) provided by the user, Platform Generator counts the number of devices (both masters and slaves) attached to the OPB, instantiates opb_v20, and automatically connects the address bus, data buses, control and arbitration signals. The Platform Generator flow allows the user to focus on designing the peripherals without having to worry about the system-level connections. Note that all masters and slaves in the system must drive data buses to zero when they are inactive, and this has to be done internally within masters and slaves. OPB supports multiple master devices as shown in the diagram above. Therefore, an arbiter is required to arbitrate the bus ownerships between masters. If there is only one OPB master in the system, the OPB arbiter can still be included in the system, since the arbiter also asserts the OPB time-out signal if a slave response is not detected within 16 clock cycles. Interface Signals The interface signals are usually defined in the early design stages, with some adjustments made in the later stages. This section lists the signals required for the OPB slave and Figure 3: Physical Implementation of OPB in MicroBlaze System OPB Master Device 1 m1m_dbus m1m_request mi_opb_mgrant m1m_abus opb_dbus OPB Master Device 2 OPB Arbiter m2m_abus m2m_request opb_dbus m2m_dbus m2opb_mgrant opb_v20 OPB Slave Device 1 OPB Slave Device 2 AND gate or FDRE opb_abus opb_dbus s1s_dbus s2s_dbus AND gate or FDRE xip2045 4 www.xilinx.com February 8, 2002 1-800-255-7778 Tutorial: Designing Custom OPB Slave Peripherals for MicroBlaze R includes optional signals for reference. Figure 4 shows the OPB Slave Interface and Table 1 lists and describes the Global Signals. Figure 4: OPB Slave Interface Table 1: Global Signals Signal Name Direction Width Description OPB_Clk Input 1 All signals on the OPB are active high and are either direct output of edge-triggered latches which are clocked by the OPB_Clk or are derived from the output of a register using several levels of combinatorial logic. All input signals should be captured in the OPB masters or OPB slaves on the rising edge of the OPB_Clk. OPB_Rst Input 1 The active high reset vector is asynchronous to the OPB_Clk. The same reset signal also goes to MicroBlaze core reset. OPB Slave <Sln>_errAck <Sln>_retry <Sln>_DBus <Sln>_xferAck <Sln>_toutSup OPB_RNW OPB_seqAddr OPB_ABus OBP_select OPB_BE OPB_DBus OPB Bus Logic xip2046 February 8, 2002 www.xilinx.com 5 1-800-255-7778 Interface Signals R Table 2 lists and describes the OPB Interface Signals. Table 2: OPB Interface Signals Signal Name Direction Width Description OPB_ABus Input [0:31] OPB_ABus is the address bus driven by the OPB bus and received by all slaves. The address on this bus is valid only when OPB_select is asserted. OPB_BE Input [ 0:3 ] OPB_BE is the byte-enable driven by the OPB bus. This signal indicates the bytes to be transferred within the data path. See the section, “Read Data Steering and Write Data Mirroring” for information on mapping data byte enables to the data paths. OPB_DBus Input [0:31] OPB_DBus is the write data bus driven by the OPB bus and received by all slaves. OPB_DBus remains valid until the master receives transfer acknowledgement for write operation. OPB_RNW Input 1 OPB_RNW (read not write) signal indicates the direction of data transfer. The signal will be valid any time OPB_select is asserted. 1 Master performs read operation on slave 0 Master performs write operation on slave OPB_select Input 1 OPB_select is driven by the OPB bus to indicate when OPB transfer is in progress and to validate the following signals: OPB_ABus, OPB_BE, OPB_RNW and OPB_seqAddr. OPB_select will continue to be driven until the master receives transfer acknowledge or retry. Deasserting OPB_select before receiving transfer acknowledge constitutes a master abort. OPB_seqAddr Input 1 OPB sequential address. The signal indicates that the transfer being performed will be followed by a transfer to the next sequential address in the same direction. When OPB_seqAddr is asserted, the slave device can arrange a reservation buffer or lock the secondary buses to improve data transfer performance, or the slave can ignore OPB_seqAddr. However, OPB_seqAddr does not indicate a burst transaction. <Sln>_DBus Output [0:31] <Sln>_DBus is the read data bus driven by the target slave. The slave device must drive valid data on <Sln>_Dbus prior to the end of the <Sln>_xferAck assertion cycle. <Sln> indicates the name of the peripheral. 6 www.xilinx.com February 8, 2002 1-800-255-7778 Tutorial: Designing Custom OPB Slave Peripherals for MicroBlaze R <Sln>_xferAck Output 1 OPB transfer acknowledge. The signal is asserted by the addressed slave to indicate the completion of a data transfer between the OPB master and slave. It is asserted for only one cycle per data transfer. In the case of write operations, this means that the slave has accepted the data, which presently appears on the data bus, or will do so at the end of this cycle. In the case of read operations, this means that the slave has placed the data to be transferred to the OPB master on the data bus or will drive the data on the data bus prior to the end of this cycle. <Sln>_xferAck must be asserted by the slave device within 16 cycles of OPB_select to prevent a timeout, unless <Sln>_ToutSup is asserted. <Sln>_xferAck must not be asserted if <Sln>_retry is asserted. <Sln>_xferAck also qualifies <Sln>_errAck. <Sln> indicates the name of the peripheral. <Sln>_retry Output 1 OPB bus cycle retry. This signal is asserted by an OPB slave to indicate that it is unable to perform the requested transfer at this time. <Sln>_retry remains asserted until the slave becomes deselected as a result of OPB_select reassertion. <Sln>_retry implies the request to master to terminate the transfer. The primary use of <Sln>_retry enables slave devices to break possible arbitration deadlock. <Sln> indicates the name of the peripheral. Table 2: OPB Interface Signals (Continued) Signal Name Direction Width Description February 8, 2002 www.xilinx.com 7 1-800-255-7778 Interface Signals R Table 3 lists and describes the optional Interrupt Signals. Xilinx provides scalable Interrupt Controller, which is included in MicroBlaze development kits, to support different styles of interrupts: level sensitive, edge sensitive, active high, or active low. Custom OPB peripheral applications may have different interrupt styles and/or multiple interrupt signals. Table 4 lists and describes the optional Application Signals. <Sln>_toutSup Output 1 Slave time-out suppress. The signal is asserted by an OPB slave to indicate that the bus operation will be delayed for an extended time. This signal must be asserted within 16 clock cycles from the assertion of OPB_select to prevent a bus timeout. <Sln>_ToutSup will be used by the OPB Arbiter to disable the timeout counter and suppress the assertion of OPB_timeout. <Sln>_ToutSup must remain asserted until the slave can complete the requested operation. Note: If the master deasserts OPB_select prior to the slave asserting <Sln>_xferAck or <Sln>_retry, thereby aborting the transfer request, the Sln_toutSup signal may remain asserted for one additional clock cycle. <Sln> indicates the name of the peripheral. <Sln>_errAck Output 1 OPB transfer error acknowledge. The signal is asserted by a slave device to indicate that the slave encountered an error in performing the requested transfer. <Sln>_errAck may be asserted immediately upon a slave device's decode of its address during a transfer cycle (OPB_select asserted) or any time thereafter. It must be valid when <Sln>_xferAck is asserted. Slaves must drive their <Sln>_errAck signal only when selected; otherwise, the slave must keep its <Sln>_errAck signal deasserted. <Sln> indicates the name of the peripheral. Note: All inactive OPB slave devices should drive buses to zero. Table 3: Interrupt Signals (Optional) Signal Name Direction Width Description Example: Interrupt Output Defined by User An OPB slave device can implement one or multiple interrupt signals, depending on the system requirements. Table 4: Application Signals (Optional) Signal Name Direction Width Description Defined by User Defined by User Defined by User Defined by User Table 2: OPB Interface Signals (Continued) Signal Name Direction Width Description 8 www.xilinx.com February 8, 2002 1-800-255-7778 Tutorial: Designing Custom OPB Slave Peripherals for MicroBlaze R Each application has application-specific signals, including RX and TX in UART designs and Sda (Serial Data) and Scl (Serial Clock) in IIC designs. In the module level of HDL design, ports should be defined either as input or output. Thus, users should expand a bidirectional (inout) port to 3 separate ports: 2 outputs and 1 input. The 2 outputs will be the output port and the tristate (enable) port of the inout. The input will be the input port to the inout. The names may correspond to the convention <ioname>_T, <ioname>_O, and <ioname>_I, where <ioname> can be your bidirectional signal name; for example, GPIO_T, GPIO_O and GPIO_I. Generics (Optional) It is recommended that generics be used, rather than hard-coded values, to make the design reusable and retargetable. For example, generics can be used in the baud rate and data bit for the UART, the time interval for the watchdog timer, etc. Therefore, when the specification of a peripheral has to be updated, the user can easily modify the generics without changing the source code. Notice that Platform Generator has keywords towards attributes names. Platform Generator does automatic expansion on certain reserved attributes, such as C_OPB_DWIDTH and C_OPB_AWIDTH. Therefore, users will have to refer to the Platform Generator reference guide for the list of reserved attribute names. Table 5 lists and describes the optional Generic Names. Table 5: Generics (Optional) Generic Name Type Width Description C_BASEADDR std_logic_vector [0:31] The base address of this memory- mapped slave device. When a master initiates an operation by asserting OPB_select, the address decode logic may reference this value and compare with OPB_ABus to determine whether this slave has been targeted by the master. C_BASEADDR is a keyword attribute for Platform Generator. C_HIGHADDR std_logic_vector [0:31] The high address of this memory- mapped slave device. Together with the base address, the total memory space is defined. C_HIGHADDR is a keyword attribute for Platform Generator. C_OPB_DWIDTH integer - OPB System data bus width. MicroBlaze employs 32 2-bit OPB architecture, so this value should be fixed to 32. C_OPB_AWIDTH integer - OPB System address bus width. MicroBlaze employes 32-bit OPB architecture, so this value should be fixed to 32. Others (Defined by User) - - - February 8, 2002 www.xilinx.com 9 1-800-255-7778 Generic Block Diagram R Generic Block Diagram An OPB slave design example consists of the following components: • Address decoding logic • OPB slave interface logic • Application-specific logic Figure 5 is a block diagram example for an OPB Slave. Address Decoding Logic Each OPB slave device should have its own address decoding logic. When OPB_select is asserted and OPB_ABus is valid, all OPB slave devices will decode the coming address and determine whether to respond or to ignore. If OPB slave devices are not targeted by the master which has been granted the ownership of the bus, the slaves must output all zeros for all OPB-related interface signals. The user will want to make sure there is no overlap in memory-mapped space allocation. Otherwise, multiple OPB slave devices may try to respond to the same transaction, leading to system malfunctions. Since address decoding logic sometimes is a critical path for timing, the MicroBlaze development kit provides a sample for parameterizable peripheral address decoding logic written in VHDL. The file is named pselect.vhd. The file pselect.vhd is a general-purpose decoding logic targeting Xilinx FPGA families for best area and timing optimization. This module can also be reused in bus systems other than the OPB system. If this file is not available in the development kit, users can always design a simple comparator to determine address. Figure 5: A Block Diagram Example for an OPB Slave OPB_ABus OPB_select Addr match (Peripheral select) OPB_DBus OPB_BE Application- specific logic REG FDRE REG <Sln>_DBus <Sln>_xferAck Applications Read data Address decoding logic (EX: pslect.vhd) OPB Slave I/F logic REG OPB Bus Q D R xfer_Ack xip2047 10 www.xilinx.com February 8, 2002 1-800-255-7778 Tutorial: Designing Custom OPB Slave Peripherals for MicroBlaze R Table 6 shows the generics and I/O interface of pselect.vhd. Note that pselect utilizes purely combinatorial logic and the user must analyze the timing arch through pselect and register the output signal “PS” prior to use, if necessary. Table 7 shows the I/O signal names of the interface of pselect.vhd. OPB Slave Interface Logic Once the slave has decoded its address and determined to respond to the transaction, this OPB slave interface logic handles the handshake, protocol, etc. See “Interface Signals and the Timing Diagram” for further details. Application-Specific Logic For each application, application-specific logic must be defined by the user. Table 6: Generics of pselect.vhd Generic Name Type Width Description C_AB Integer - Number of the most significant bit on the address bus to be decoded. If C_AB gets larger value, more bits must be compared with input address. In this case, less memory-mapped space is defined for this slave peripheral. C_AW Integer - Width of the input address bus. In MicroBlaze’s current MDT flow, C_AW should have a fixed value of 32. C_BAR std_logic_vector 32 Base address of this slave peripheral. When the C_AB most significant address bits match the C_AB most significant C_BAR bits, PS (peripheral select) is asserted. Table 7: I/O Interface of pselect.vhd Signal Name Direction Width Description A Input [0:C_AW-1] Address input. In the OPB subsystem, this should be connected to OPB_ABus, or a registered input of OPB_ABus, depending on timing requirement. Avalid Input 1 Address valid. In the OPB subsystem, this should be connected to OPB_select, or a registered input of OPB_select, depending on the timing requirement. PS Output 1 Peripheral select. When the C_AB most significant address bits match the C_AB most significant C_BAR bits, PS is asserted. As PS is not a registered output from pselect.vhd, the user must register this signal before using it. February 8, 2002 www.xilinx.com 11 1-800-255-7778 Timing Diagram R Timing Diagram Figure 6 shows basic OPB read transactions and Figure 7 shows basic OPB write transactions. The OPB master asserts OPB_select and puts valid OPB_ABus, OPB_BE and OPB_RNW on the buses. The slave completes the transfer by asserting OPB_xferAck, which causes the master to latch data from the data bus on read transfers, and deassert select. Note that the cycles for the OPB master device asserting its request to the OPB arbiter is not shown in these diagrams. Also refer to OPB 2.1 Specification from IBM for other protocol definition. Figure 6: A Basic OPB Read Transaction (Example) 12 www.xilinx.com February 8, 2002 1-800-255-7778 Tutorial: Designing Custom OPB Slave Peripherals for MicroBlaze R Read Data Steering and Write Data Mirroring (MicroBlaze Only) In the MicroBlaze processor, an OPB master device performs read data steering and write data mirroring. Users should be aware of the data byte mapping mechanism MicroBlaze applies in OPB Read (load instructions) and OPB Write (store instructions) operations, in order to design the slave peripherals that meet the expectations of MicroBlaze as the master peripheral in the system. MicroBlaze’s Read Data Steering (Load to register rD) Table 8 shows how MicroBlaze performs read data steering, i.e., how the internal register rD will be loaded with the data bytes appearing on the 32-bit read data bus. Figure 7: A Basic OPB Write Transaction (Example) Table 8: MicroBlaze’s Read Data Steering (Load to Register rD) Register rD Data OPB_ABus [30:31] OPB_BE [0:3] Transfer Size rD[0:7] rD[8:15] rD[16:23] rD[24:31] 11 0001 Byte Byte 3 10 0010 Byte Byte 2 01 0100 Byte Byte 1 00 1000 Byte Byte 0 10 0011 Halfword Byte 2 Byte 3 February 8, 2002 www.xilinx.com 13 1-800-255-7778 Bus Alignment R Users must pay attention to this table and place data bytes properly to the read data bus. MicroBlaze’s Write Data Mirroring (Store from register rD) Write data is mirrored to all byte lanes by MicroBlaze, giving the slave devices flexibility to attach to the write bus. For example, a device with internal ping-pong buffers can benefit from the write data mirror without extra muxes and a byte device can be attached to any byte lane. However, users cannot assume that all OPB master devices perform write data mirroring. Table 9 shows how MicroBlaze does write data mirroring. The fields in Bold are defined by the OPB spec and PLB2OPB spec, and the fields in Italic are the mirroring feature MicroBlaze provides additionally. a Bus Alignment Platform Generator requires OPB data buses to be 32 bits wide. Therefore, any legacy devices of bus width less than 32 bits must expand the bus width properly. There are several ways to handle this case, depending on the nature of the devices. If a device contains memory based design that requires some restrictions in the storage mode, the appropriate steering logic may be included to take care of the data alignment. The user can compare the behavior of the legacy design with Table 8 and Table 9 to design the steering logic for MicroBlaze. If the legacy design contains register-based devices and physical bus connection is not an issue, the unused byte lanes in a 32-bit Read Dada bus can be tied to zero as Figure 8 shows. In this case, the addressing mode can always align to word boundary, i.e., the peripheral always ignores OPB_ABus[30:31]. For example, in a C program, simply use “int” (integer, 32bit) instead of “char” (character, 8bit) declarations. Doing this will align the OPB_ABus to the word boundaries and the slave devices may drop OPB_ABus[30:31] internally. 00 1100 Halfword Byte 0 Byte 1 00 1111 Word Byte 0 Byte 1 Byte 2 Byte 3 In the big endian notation, byte 0 is Read Data Bus [0:7], byte 1 is Read Data Bus [8:15], byte 2 is Read Data Bus [16:23], and byte 3 is Read Data Bus [24:31]. Table 8: MicroBlaze’s Read Data Steering (Load to Register rD) Table 9: MicroBlaze’s Write Data Mirroring (Store from Register rD) Write Data Bus OPB_ABus [30:31] OPB_BE [0:3] Transfer Size OPB_DBus [0:7] OPB_DBus [8:15] OPB_DBus [16:23] OPB_DBus [24:31] 11 0001 Byte rD[24:31] rD[24:31] rD[24:31] rD[24:31] 10 0010 Byte rD[24:31] rD[24:31] rD[24:31] rD[24:31] 01 0100 Byte rD[24:31] rD[24:31] rD[24:31] rD[24:31] 00 1000 Byte rD[24:31] rD[24:31] rD[24:31] rD[24:31] 10 0011 Halfword rD[16:23] rD[24:31] rD[16:23] rD[24:31] 00 1100 Halfword rD[16:23] rD[24:31] rD[16:23] rD[24:31] 00 1111 Word rD[0:7] rD[8:15] rD[16:23] rD[24:31] 14 www.xilinx.com February 8, 2002 1-800-255-7778 Tutorial: Designing Custom OPB Slave Peripherals for MicroBlaze R In conclusion, the various factors designers must consider in determining how the data bus should align include the nature of the device, the read data steering and write data mirroring mechanism (MicroBlaze only), and communicating well with firmware designers to avoid mistakes. General Coding Guidelines Some general RTL coding guidelines: • Register input signals and output signals to improve timing • Use Clock Enables instead of using different clock domains • Register OPB signal outputs from slave devices by using FDRE components. Use OPB_xferAck to reset the register synchronously • For any device smaller than 32bit, expand the data buses to 32-bit width, with appropriate steering logic, or tie unused byte lanes to zeros, as the case requires Figure 8: Expand a Byte Device to 32 Bits Wide zeros <Sln>_Dbus [0:31] 00 00 00 AB 24 8 Byte device core xip2050 February 8, 2002 www.xilinx.com 15 1-800-255-7778 General Coding Guidelines R The next section uses MYGPIO as a design example, based on the topics discussed in the preceding sections. MYGPIO is a simple peripheral consisting of three memory-mapped registers for software access. Figure 9 shows the block diagram for MYGPIO. entity MYGPIO is generic ( C_OPB_AWIDTH : integer := 32; C_OPB_DWIDTH : integer := 32; C_BASEADDR : std_logic_vector(0 to 31) := X"FFFF_8000"; C_HIGHADDR : std_logic_vector(0 to 31) := X"FFFF_80FF" ); port ( -- Global signals OPB_Clk : in std_logic; OPB_Rst : in std_logic; Interrupt : out std_logic; -- OPB signals OPB_ABus : in std_logic_vector(0 to C_OPB_AWIDTH-1); OPB_BE : in std_logic_vector(0 to C_OPB_DWIDTH/8-1); OPB_DBus : in std_logic_vector(0 to C_OPB_DWIDTH-1); OPB_RNW : in std_logic; OPB_select : in std_logic; OPB_seqAddr : in std_logic; GPIO_DBus : out std_logic_vector(0 to C_OPB_DWIDTH-1); GPIO_errAck : out std_logic; GPIO_retry : out std_logic; GPIO_toutSup : out std_logic; GPIO_xferAck : out std_logic; -- GPIO signals GPIO_IO_I : in std_logic_vector(0 to 7); --GPIO input GPIO_IO_O : out std_logic_vector(0 to 7); --GPIO output GPIO_IO_T : out std_logic_vector(0 to 7) --GPIO tri-state ouput ); end entity MYGPIO; Figure 10 shows the entity declaration that describes the interface of the design to its external environment. In the generic declaration, C_OPB_AWIDTH and C_OPB_DWIDTH Figure 9: Block Diagram for MYGPIO Figure 10: Entity of MYGPIO OPB I/F Offset x00 GPIO/I Offset x04 GPIO/O Offset x08 GPIO/T GPIO MYGPIO OPB xip2151 16 www.xilinx.com February 8, 2002 1-800-255-7778 Tutorial: Designing Custom OPB Slave Peripherals for MicroBlaze R define the width for address bus and data buses. The parameterized coding style provides more flexibility to target different bus standards for future expansion. In the MicroBlaze system, since dynamic bus sizing is not supported and Platform Generator supports 32-bit address and data buses, C_OPB_AWIDTH and C_OPB_DWIDTH should be 32. C_BASEADDR and C_HIGHADDR define the memory-mapped space for MYGPIO in the embedded system defined by the user. The port declaration uses: • Global signals: OPB_Clk and OPB_Rst • OPB signals: OPB_ABus, OPB_BE, OPB_RNW, OPB_select, OPB_seqAddr, OPB_DBus, GPIO_DBus, GPIO_errAck, GPIO_retry, GPIO_toutSup, GPIO_xferAck • GPIO signals: GPIO_IO_I, GPIO_IO_O, and GPIO_IO_T The width of GPIO_DBus (the read bus output from MYGPIO) is 32 bits wide, even though MYGIPO has an 8-bit core. In this example, only GPIO_DBus[24:31] is used, while GPIO_DBus[0:23] is tied to zero. Platform Generator requires that all OPB address and OPB read/write data buses in the VHDL entity be to std_logic_vector (0 to 31). Figure 11 is an example VHDL code utilizing all the topics discussed in the preceding sections. architecture RTL of MYGPIO is -- Special function to calculate number of bits need to be decoded -- based on C_BASEADDR and C_HIGHADDR. -- If C_BASEADDR = X"FFFF_8000" and C_HIGHADDR = X"FFFF_80FF", -- the function returns 24. function Addr_Bits (x, y : std_logic_vector(0 to C_OPB_AWIDTH-1)) return integer is variable addr_nor : std_logic_vector(0 to C_OPB_AWIDTH-1); begin addr_nor := x xor y; for i in 0 to C_OPB_AWIDTH-1 loop if addr_nor(i) = '1' then return i; end if; end loop; return(C_OPB_AWIDTH); end function Addr_Bits; constant C_AB : integer := Addr_Bits(C_OPB_HIGHADDR, C_OPB_BASEADDR); ... ... begin -- architecture RTL ----------------------------------------------------------------- -- Handling the OPB bus interface ----------------------------------------------------------------- -- OPB address decoding using pselect.vhd. -- The generic map C_BASEADDR is passed from entity, -- C_AB is the return value from function Addr_Bits(). -- If C_AB gets smaller, the logic of pselect gets smaller. -- -- OPB_ABus and OPB_select come from the ports. -- gpio_CS will be registered prior to usage. -- Use OPB_ABus_reg and OPB_select_reg if non-registered -- signals don’t meet timing. pselect_I : pselect generic map ( C_AB => C_AB, February 8, 2002 www.xilinx.com 17 1-800-255-7778 General Coding Guidelines R C_AW => OPB_ABus'length, C_BAR => C_BASEADDR) port map ( A => OPB_ABus, AValid => OPB_select, ps => jtag_UART_CS); -- First register gpio_CS generated by pselect -- uart_CS_1_DFF is synchronously reseted by xfer_Ack -- (or OPB_xferAck) when the current transaction has -- been completed by the slave. gpio_CS_1_DFF : FDR port map ( Q => gpio_CS_1, -- [out std_logic] C => OPB_Clk, -- [in std_logic] D => gpio_CS, -- [in std_logic] R => xfer_Ack); -- [in std_logic] gpio_CS_2_DFF : process (OPB_Clk, OPB_Rst) is begin if OPB_Rst = '1' then gpio_CS_2 <= '0'; elsif OPB_Clk'event and OPB_Clk = '1' then gpio_CS_2 <= gpio_CS_1 and not gpio_CS_2 and not xfer_Ack; end if; end process gpio_CS_2_DFF; -- Register OPB read data output. Synchronously reseted -- by xfer_Ack (or OPB_xferAck) when the current -- transaction has been completed by the slave. -- -- xfer_Ack is a cycle delay to gpio_CS_2, so that -- the OPB_rdBus_FDRE will be synchronously reseted -- a cycle after clock enable. OPB_rdDBus_DFF : for I in 0 to 7 generate OPB_rdBus_FDRE : FDRE port map ( Q => Sln_DBus(I), C => Clk, CE => gpio_CS_2, D => sln_DBus_i(I), R => xfer_Ack); end generate OPB_rdDBus_DFF; XFER_Control : process (OPB_Clk, OPB_Rst) is begin if OPB_Rst = '1' then xfer_Ack <= '0'; elsif OPB_Clk'event and OPB_Clk = '1' then xfer_Ack <= gpio_CS_2; end if; end process XFER_Control; GPIO_xferAck <= xfer_Ack; GPIO_DBus(24 to 31) <= Sln_DBus; -- Tie unused signals to groud GPIO_DBus(0 to 23) <= (others => '0'); GPIO_errAck <= '0'; GPIO_retry <= '0'; GPIO_toutSup <= '0'; ----------------------------------------------------------------- 18 www.xilinx.com February 8, 2002 1-800-255-7778 Tutorial: Designing Custom OPB Slave Peripherals for MicroBlaze R -- Register all the OPB input signals ----------------------------------------------------------------- WRDBUS_FF_GENERATE: for i in 0 to 7 generate WRDBUS_FF_I: FDR port map ( Q => opb_DBus_Reg(i), C => OPB_Clk, D => OPB_DBus(24 to 31), R => OPB_Rst ); end generate WRDBUS_FF_GENERATE; ABUS_FF_GENERATE: for i in 0 to C_OPB_AWIDTH-1 generate ABUS_FF_I: FDR port map ( Q => opb_ABus_Reg(i), C => OPB_Clk, D => OPB_ABus(i), R => OPB_Rst ); end generate ABUS_FF_GENERATE; RNW_FF_I: FDR port map ( Q => opb_RNW_Reg, C => OPB_Clk, D => OPB_RNW, R => OPB_Rst ); ----------------------------------------------------- -- Memory Mapped Registers Write Access for MYGPIO ----------------------------------------------------- -- The C program chose to use an integer(32bit) pointer -- to addresses aligned to word boundaries (0,4,8,c..) -- even though MYGPIO has 8 bit only. -- So bit 30:31 of OPB_ABus are dropped so that the Address -- port of GPIO core is always aligned to word boundary. -- -- Generate enable signals based on address and write cmd. gpdata_out_we <= '1' when (opb_ABus_Reg(28) = '0' and opb_ABus_Reg(29) = '1' and opb_RNW_Reg = '0' and gpio_CS_2 = '1') else '0'; gpdata_tri_we <= '1' when (opb_ABus_Reg(28) = '1' and opb_ABus_Reg(29) = '0' and opb_RNW_Reg = '0'and gpio_CS_2 = '1') else '0'; --Offset 00 GPIO DATA INPUT (Read only) REG_00: process (OPB_Clk, OPB_Rst) is begin if OPB_Rst = '1' then gpdata_in <= '0'; elsif OPB_Clk'event and OPB_Clk = '1' then gpdata_in <= GPIO_IO_I; --from external pin end if; end process REG_00; --Offset 04 GPIO DATA OUTPUT (R/W) default value 0 REG_04: process (OPB_Clk, OPB_Rst) is begin if OPB_Rst = '1' then February 8, 2002 www.xilinx.com 19 1-800-255-7778 General Coding Guidelines R gpdata_out <= '0'; elsif OPB_Clk'event and OPB_Clk = '1' then if (gpdata_out_we = '1') gpdata_out <= opb_DBus_Reg; -- to external pin end if; end process REG_04; --Offset 08 GPIO DATA Tri-State OUTPUT (R/W) default value 1 REG_08: process (OPB_Clk, OPB_Rst) is begin if OPB_Rst = '1' then gpdata_tri <= (others => '1'); elsif OPB_Clk'event and OPB_Clk = '1' then if (gpdata_tri_we = '1') gpdata_tri <= opb_DBus_Reg; --to external pin end if; end process REG_08; --------------------------------------------------- -- Memory Mapped Registers Read MUX for MYGPIO --------------------------------------------------- with opb_ABus_Reg(28 to 29) select sln_DBus_i <= gpdata_in when "00", gpdata_out when "01", gpdata_tri when "10", (others => '0') when others; ... ... ... end architecture RTL; Figure 12 is the timing diagram for OPB slave interface. Figure 11: Implementation Example of MYGPIO Figure 12: Timing Diagram for the OPB Slave Interface OPB_CLK OPB_Select OPB_ABus gpio_CS gpio_CS1 gpio_CS2 data valid data 0000 sln_DBus_i(0:7) Sln_DBus(0:7) gpio_xferAck 0000 Valid Address xip2052 20 www.xilinx.com February 8, 2002 1-800-255-7778 Tutorial: Designing Custom OPB Slave Peripherals for MicroBlaze R PRELIMINARYPRELIMINARYIntroduction to OPB IPIF (Preliminary) In the above design practice for MYGPIO, a simple way to design OPB slaves with only memory-mapped registers was discussed. In addition to registers, an OPB slave peripheral may contain other basic components that must be accessed and controlled by the high- level firmware. These components can be FIFOs, DMA, software reset, interrupt support, etc. When the RTL designers start to build the entire embedded system, many procedures in the design of these components are repetitive. The OPB IPIF provided via CoreGen flow, is a module for attaching an intellectual property to the OPB, providing common components OPB slaves (and also masters) may require. IPIF stands for Intellectual Property Interface. The OPB IPIF was conceived to provide a common interface for third-party IP providers and customers wanting to integrate their own cores into MicroBlaze systems, designed to reduce the repetitive development effort needed to connect IP to the OPB bus, and promoting higher quality of consistency. The OPB IPIF basically has two functions: (1) to facilitate attachment of devices to the OPB in a standard way and (2) to provide services that are useful to various classes of IPs. Figure 13 shows an OPB device using the full set of IPIF features. This device has both Master and Slave attachments, Address Decode, Interrupt Control, Read Packet FIFOs, Write Packet FIFOs, DMA, and Scatter Gather. The IPIF is a parametric soft IP core designed for Xilinx FPGAs, available through CoreGen flow. Therefore, it is very simple to choose the minimal set of required functions and appropriate master or slave attachment. In the MYGPIO example, because FIFOs and DMAs are not used, CoreGen can generate the IPIF with nothing more than OPB slave access to the memory-mapped registers. Figure 14 shows the minimal set of IPIF that fits MYGPIO’s requirements. Figure 13: An OPB Device Using the Full set of IPIF Features IPC and "glue" Interrupt Control Register I/F Reset Slave Attachment "SRAM" I/F Addr_Decode Write FIFO Read FIFO Master I/F Scatter Gather DMA Master Attachment OPB Control Data Path IP Core External I/F IPIF Device IP Interconnect xip2053 February 8, 2002 www.xilinx.com 21 1-800-255-7778 Design Practice Using OPB IPIF (Preliminary) R PRELIMINARYPRELIMINARYDesign Practice Using OPB IPIF (Preliminary) Since OPB IPIF has handled the OPB protocol, the users have to learn only how to attach their own IP core to the IP interconnect shown in the above diagram. Figure 15 shows the same MYGPIO design but using OPB IPIF’s simple register interface. Comparing to the previous example, the logic required to design it has been reduced because of instantiating OPB IPIF. architecture RTL2 of MYGPIO is ------------------------------------------------------------------ -- Calculate Number of bits in AddresS that need to decode ------------------------------------------------------------------ -- Special function to calculate number of bits need to be decoded -- based on C_BASEADDR and C_HIGHADDR. -- If C_BASEADDR = X"FFFF_8000" and C_HIGHADDR = X"FFFF_80FF", -- the function returns C_AB=24. function Addr_Bits (x, y : std_logic_vector(0 to C_OPB_AWIDTH-1)) return integer is variable addr_nor : std_logic_vector(0 to C_OPB_AWIDTH-1); begin addr_nor := x xor y; for i in 0 to C_OPB_AWIDTH-1 loop if addr_nor(i) = '1' then return i; end if; end loop; return(C_OPB_AWIDTH); end function Addr_Bits; constant C_AB : integer := Addr_Bits(C_HIGHADDR, C_BASEADDR); Figure 14: An OPB Device Using Only the IPIF Features for Register Access IPC and "glue" Register I/F Slave Attachment Addr_Decode OPB Control Data Path IP Core External I/F IPIF Device IP Interconnect xip2054 22 www.xilinx.com February 8, 2002 1-800-255-7778 Tutorial: Designing Custom OPB Slave Peripherals for MicroBlaze R PRELIMINARYPRELIMINARY----------------------------------------------------------------- -- Component template from CoreGen ----------------------------------------------------------------- -- The following component delaration can be generated by CoreGen -- The generics contains full set of features provided by IPIF. -- Users can turn on/off the features based on the applications. -- Some generics will be over-written by the instantiation later -- in the architecture section -- -- The names of parameters and signals are self-document. Refer to -- OPB IPIF Architecture Specification for detailes. component ipif generic ( C_DEV_BLK_ID : INTEGER := 0; C_DEV_MIR_ENABLE : BOOLEAN := False; C_DEV_BASEADDR : std_logic_vector := X"FFFF_8000"; C_OPB_ABUS_WIDTH : INTEGER := 32; C_OPB_DBUS_WIDTH : INTEGER := 32; C_OPB_BE_NUM : INTEGER := 4; C_DEV_BURST_ENABLE : BOOLEAN := False; C_DEV_MAX_BURST_SIZE : INTEGER := 64; C_RESET_PRESENT : BOOLEAN := False; C_INTERRUPT_PRESENT : BOOLEAN := True; C_INCLUDE_DEV_PENCODER : BOOLEAN := False; C_IP_MASTER_PRESENT : BOOLEAN := False; C_IP_REG_PRESENT : BOOLEAN := True; C_IP_REG_NUM : INTEGER := 3; C_IP_IRPT_NUM : INTEGER := 1; C_IP_SRAM_PRESENT : BOOLEAN := False; C_IP_SRAM_BASEADDR_OFFSET : std_logic_vector := X"00001000"; C_IP_SRAM_SIZE : INTEGER := 256; C_WRFIFO_PRESENT : BOOLEAN := False; C_WRFIFO_BASEADDR_OFFSET : std_logic_vector := X"00002100"; C_WRFIFO_REG_BASEADDR_OFFSET: std_logic_vector := X"00002000"; C_RDFIFO_PRESENT : BOOLEAN := False; C_RDFIFO_BASEADDR_OFFSET : std_logic_vector := X"00002200"; C_RDFIFO_REG_BASEADDR_OFFSET: std_logic_vector := X"00002010"; C_DMA_PRESENT : BOOLEAN := False; C_DMA_REG_BASEADDR_OFFSET : std_logic_vector := X"00002300"; C_DMA_CHAN_NUM : INTEGER := 2; C_DMA_CH1_TYPE : INTEGER := 2; C_DMA_CH2_TYPE : INTEGER := 3; C_DMA_ALLOW_BURST : BOOLEAN := False; C_DMA_LENGTH_WIDTH : INTEGER := 11; C_DMA_INTR_COALESCE : BOOLEAN := False; C_DMA_PACKET_WAIT_UNIT_NS : INTEGER := 1000000; C_DMA_TXL_FIFO_IPCE : INTEGER := 8; C_DMA_TXS_FIFO_IPCE : INTEGER := 9; C_DMA_RXL_FIFO_IPCE : INTEGER := 7; C_DMA_RXS_FIFO_IPCE : INTEGER := 15; C_OPB_CLK_PERIOD_PS : INTEGER := 10000; C_IP_REG_BASEADDR_OFFSET : std_logic_vector := X"00000100"; C_DEV_ADDR_DECODE_WIDTH : INTEGER := 24; C_IPIF_ABUS_WIDTH : INTEGER := 4; C_IPIF_DBUS_WIDTH : INTEGER := 32; C_VIRTEX_II : Boolean := True; C_INCLUDE_DEV_ISC : Boolean := False ); port ( OPB_ABus :in std_logic_vector(0 to C_OPB_ABUS_WIDTH - 1); OPB_DBus :in std_logic_vector(0 to C_OPB_DBUS_WIDTH - 1); Sln_DBus :out std_logic_vector(0 to C_OPB_DBUS_WIDTH - 1); Mn_ABus :out std_logic_vector(0 to C_OPB_ABUS_WIDTH - 1); IP2Bus_Addr :in std_logic_vector(0 to C_OPB_ABUS_WIDTH - 1); Bus2IP_Addr :out std_logic_vector(0 to C_IPIF_ABUS_WIDTH - 1); Bus2IP_Data :out std_logic_vector(0 to C_IPIF_DBUS_WIDTH - 1); February 8, 2002 www.xilinx.com 23 1-800-255-7778 Design Practice Using OPB IPIF (Preliminary) R PRELIMINARYPRELIMINARYBus2IP_Reg_RdCE :out std_logic_vector(0 to C_IP_REG_NUM - 1); Bus2IP_Reg_WrCE :out std_logic_vector(0 to C_IP_REG_NUM - 1); Bus2IP_SRAM_CE :out std_logic; IP2Bus_Data :in std_logic_vector(0 to C_IPIF_DBUS_WIDTH - 1); IP2Bus_WrAck :in std_logic; IP2Bus_RdAck :in std_logic; IP2Bus_Retry :in std_logic; IP2Bus_Error :in std_logic; IP2Bus_ToutSup :in std_logic; IP2DMA_RxLength_Empty : in std_logic; IP2DMA_RxStatus_Empty : in std_logic; IP2DMA_TxLength_Full : in std_logic; IP2DMA_TxStatus_Empty : in std_logic; IP2IP_Addr :in std_logic_vector(0 to C_IPIF_ABUS_WIDTH - 1); IP2RFIFO_Data :in std_logic_vector(0 to 31); IP2RFIFO_WrMark :in std_logic; IP2RFIFO_WrRelease :in std_logic; IP2RFIFO_WrReq :in std_logic; IP2RFIFO_WrRestore :in std_logic; IP2WFIFO_RdMark :in std_logic; IP2WFIFO_RdRelease :in std_logic; IP2WFIFO_RdReq :in std_logic; IP2WFIFO_RdRestore :in std_logic; IP2Bus_MstBE :in std_logic_vector(0 to C_OPB_BE_NUM - 1); IP2Bus_MstWrReq :in std_logic; IP2Bus_MstRdReq :in std_logic; IP2Bus_MstBurst :in std_logic; IP2Bus_MstBusLock :in std_logic; Bus2IP_MstWrAck :out std_logic; Bus2IP_MstRdAck :out std_logic; Bus2IP_MstRetry :out std_logic; Bus2IP_MstError :out std_logic; Bus2IP_MstTimeOut :out std_logic; Bus2IP_MstLastAck :out std_logic; Bus2IP_BE :out std_logic_vector(0 to C_OPB_BE_NUM - 1); Bus2IP_WrReq :out std_logic; Bus2IP_RdReq :out std_logic; Bus2IP_Burst :out std_logic; Mn_request :out std_logic; Mn_busLock :out std_logic; Mn_select :out std_logic; Mn_RNW :out std_logic; Mn_BE :out std_logic_vector(0 to C_OPB_BE_NUM - 1); Mn_seqAddr :out std_logic; OPB_MnGrant :in std_logic; OPB_xferAck :in std_logic; OPB_errAck :in std_logic; OPB_retry :in std_logic; OPB_timeout :in std_logic; Freeze :in std_logic; RFIFO2IP_AlmostFull :out std_logic; RFIFO2IP_Full :out std_logic; RFIFO2IP_Vacancy :out std_logic_vector(0 to 9 ); RFIFO2IP_WrAck :out std_logic; OPB_select :in std_logic; OPB_RNW :in std_logic; OPB_seqAddr :in std_logic; OPB_BE :in std_logic_vector(0 to C_OPB_BE_NUM - 1); Sln_xferAck :out std_logic; Sln_errAck :out std_logic; Sln_toutSup :out std_logic; Sln_retry :out std_logic; WFIFO2IP_AlmostEmpty:out std_logic; WFIFO2IP_Data :out std_logic_vector(0 to 31 ); WFIFO2IP_Empty :out std_logic; WFIFO2IP_Occupancy :out std_logic_vector(0 to 9 ); WFIFO2IP_RdAck :out std_logic; Bus2IP_Clk :out std_logic; 24 www.xilinx.com February 8, 2002 1-800-255-7778 Tutorial: Designing Custom OPB Slave Peripherals for MicroBlaze R PRELIMINARYPRELIMINARYBus2IP_DMA_Ack :out std_logic; Bus2IP_Freeze :out std_logic; Bus2IP_Reset :out std_logic; IP2Bus_Clk :in std_logic; IP2Bus_DMA_Req :in std_logic; IP2Bus_IntrEvent :in std_logic_vector(0 to C_IP_IRPT_NUM - 1); IP2INTC_Irpt :out std_logic; OPBClk :in std_logic; Reset :in std_logic ); end component; ... ... ... begin -- architecture RTL2 --------------------------------------------------------------------------- -- Instantiate OPB_IPIF to handle OPB interface --------------------------------------------------------------------------- --The following section overwrites default value of generics for --MYGPIO example. Since MYGPIO only needs the "Register" feature, --other IPIF features are set to "False" --********************************************************* --* Because of readability in this document, the following* --* instantiation lists only related signals, it is not a * --* complete source code. * --********************************************************* u0_ipif: ipif generic map ( ... ... C_DEV_BASEADDR => C_BASEADDR, --passed from entity C_OPB_ABUS_WIDTH => C_OPB_AWIDTH,--passed from entity C_OPB_DBUS_WIDTH => C_OPB_DWIDTH,--passed from entity C_DEV_ADDR_DECODE_WIDTH => C_AB, --cal. by function Addr_Bits C_DEV_BURST_ENABLE => False, --set to false for MYGPIO C_RESET_PRESENT => False, --set to false for MYGPIO C_INTERRUPT_PRESENT => False, --set to false for MYGPIO C_INCLUDE_DEV_PENCODER => False, --set to false for MYGPIO C_IP_MASTER_PRESENT => False, --set to false for MYGPIO C_IP_REG_PRESENT => True, --set to true for MYGPIO C_IP_REG_NUM => 3, --X00/X04/X08 for MYGPIO C_IP_REG_BASEADDR_OFFSET => X"00000000", --X00 for register offset C_IP_SRAM_PRESENT => False, --set to false for MYGPIO C_WRFIFO_PRESENT => False, --set to false for MYGPIO C_RDFIFO_PRESENT => False, --set to false for MYGPIO C_DMA_PRESENT => False, --set to false for MYGPIO C_IPIF_ABUS_WIDTH => 4, --not used C_IPIF_DBUS_WIDTH => 32, --expend 8bit GPIO to 32 to avoid confusion C_INCLUDE_DEV_ISC => False,--set to false for MYGPIO ... ... .. ) port map ( .. ... ... --Interface to OPB Bus February 8, 2002 www.xilinx.com 25 1-800-255-7778 Design Practice Using OPB IPIF (Preliminary) R PRELIMINARYPRELIMINARYReset => OPB_Rst --I passed from entity OPBClk => OPB_Clk, --I passed from entity OPB_ABus => OPB_ABus, --I passed from entity OPB_DBus => OPB_DBus, --I passed from entity OPB_select => OPB_select, --I passed from entity OPB_RNW => OPB_RNW, --I passed from entity OPB_seqAddr => OPB_seqAddr, --I passed from entity OPB_BE => OPB_BE, --I passed from entity Sln_xferAck => GPIO_xferAck, --O passed to entity Sln_errAck => GPIO_errAck, --O passed to entity Sln_toutSup => GPIO_toutSup, --O passed to entity Sln_retry => GPIO_retry, --O passed to entity Sln_DBus => GPIO_DBus, --O passed to entity ... ... --IP Interconnect Interface to MYGPIO registers IP2Bus_Clk => IP2Bus_Clk, --O typically identical to OPB_CLK Bus2IP_Reset => Bus2IP_Reset, --O OPB_Rst "ORed" with SW reset. -- (SW reset is not implemented here) Bus2IP_Addr => open, --O Not Connect Bus2IP_Data => Bus2IP_Data, --O Bus2IP_Reg_RdCE => Bus2IP_Reg_RdCE,--O Bus2IP_Reg_WrCE => Bus2IP_Reg_WrCE,--O IP2Bus_Data => IP2Bus_Data, --I IP2Bus_WrAck => IP2Bus_WrAck, --I IP2Bus_RdAck => IP2Bus_RdAck, --I IP2Bus_Retry => IP2Bus_Retry, --I IP2Bus_Error => IP2Bus_Error, --I IP2Bus_ToutSup => IP2Bus_ToutSup, --I Bus2IP_BE => Bus2IP_BE, --O Bus2IP_WrReq => Bus2IP_WrReq, --O Bus2IP_RdReq => Bus2IP_RdReq, --O ... ... .. ); --Unused control signals tie to ground. IP2Bus_retry <= '0'; IP2Bus_toutSup <= '0'; IP2Bus_Retry <= '0'; IP2Bus_Error <= '0'; --------------------------------------------------- --Write Access for Memory Mapped Registers in MYGPIO --------------------------------------------------- -- The C program chose to use an integer(32bit) pointer -- to addresses aligned to word boundaries (0,4,8,c..) -- even though MYGPIO is physically 8 bit only. --Offset 00 GPIO DATA INPUT (READ ONLY) --This register cannot be written by software REG_00: process (Bus2IP_Clk, Bus2IP_Reset) is begin if Bus2IP_Reset = '1' then gpdata_in <= (others => '0'); elsif Bus2IP_Clk'event and Bus2IP_Clk = '1' then gpdata_in <= GPIO_IO_I; --from external pin end if; end process REG_00; --Offset 04 GPIO DATA OUTPUT (R/W) default value 0 REG_04: process (Bus2IP_Clk, Bus2IP_Reset) is 26 www.xilinx.com February 8, 2002 1-800-255-7778 Tutorial: Designing Custom OPB Slave Peripherals for MicroBlaze R PRELIMINARYPRELIMINARYbegin if Bus2IP_Reset = '1' then gpdata_out <= (others => '0'); elsif Bus2IP_Clk'event and Bus2IP_Clk = '1' then if ( Bus2IP_WrReq = '1' and Bus2IP_Reg_WrCE(1) = '1') then gpdata_out <= Bus2IP_Data(24 to 31); -- to external pin end if; end if; end process REG_04; --Offset 08 GPIO DATA Tri-State OUTPUT (R/W) default value 1 REG_08: process (Bus2IP_Clk, Bus2IP_Reset) is begin if Bus2IP_Reset = '1' then gpdata_tri <= (others => '1'); elsif Bus2IP_Clk'event and Bus2IP_Clk = '1' then if ( Bus2IP_WrReq = '1' and Bus2IP_Reg_WrCE(2) = '1') then gpdata_tri <= Bus2IP_Data(24 to 31); --to external pin end if; end if; end process REG_08; ------------------------------ --Assert WrAck(1-cycle pulse) --after write request ------------------------------ --Since WrReq is 1-cycle pulse in this case, --edge detection is not needed WrAck_PROCESS:process (Bus2IP_Clk,Bus2IP_Reset ) begin if (Bus2IP_Reset = '1') then IP2Bus_WrAck_i <= '0'; elsif Bus2IP_Clk'event and Bus2IP_Clk = '1' then IP2Bus_WrAck_i <= Bus2IP_WrReq; end if; end process; IP2Bus_WrAck <= IP2Bus_WrAck_i; --------------------------------------------------- --Read Mux for Memory Mapped Registers in MYGPIO --------------------------------------------------- read_process: process (Bus2IP_Clk, Bus2IP_Reset) begin if Bus2IP_Reset = '1' then read_data <= (others => '0'); elsif (Bus2IP_Clk'event and Bus2IP_Clk = '1') then if (Bus2IP_RdReq = '1') then case Bus2IP_Reg_RdCE is when "100" => read_data <= gpdata_in ; when "010" => read_data <= gpdata_out; when "001" => read_data <= gpdata_tri; when others=> read_data <= (others => '0'); end case; end if; end if; end process; IP2Bus_Data (24 to 31) <= read_data; IP2Bus_Data (0 to 23 ) <= (others => '0'); ------------------------------ --Assert RdAck(1-cycle pulse) --after read request February 8, 2002 www.xilinx.com 27 1-800-255-7778 Design Practice Using OPB IPIF (Preliminary) R PRELIMINARYPRELIMINARY------------------------------ --Since RdReq is 1-cycle pulse in this case, --edge detection is not needed RdAck_PROCESS:process (Bus2IP_Clk,Bus2IP_Reset ) begin if (Bus2IP_Reset = '1') then IP2Bus_RdAck_i <= '0'; elsif Bus2IP_Clk'event and Bus2IP_Clk = '1' then IP2Bus_RdAck_i <= Bus2IP_RdReq; end if; end process; IP2Bus_RdAck <= IP2Bus_RdAck_i; end architecture RTL2; Figure 16 and Figure 17 give examples of basic read and write transactions for IP Interconnect. There are separate per-register decodes for the read and write cases, vectors Bus2IP_RegRdCE and Bus2IP_RegWrCE, respectively. Therefore, for the register interface, the Bus2IP_RdReq and Bus2IP_WrReq signals allow the IP to easily generate a one-cycle acknowledgement, IP2Bus_RdAck or IP2Bus_WrAck, by delaying the corresponding request signal by the appropriate amount. Refer to OPB IPIF Architecture Specification for other protocol definition. Figure 15: Implementation Example of MYGPIO Using OPB IPIF Figure 16: Read Transaction for IP Interconnect Using Register Access Feature Bus2IP_Clk Bus2IP_RegRdCE(i) Bus2IP_RDReq Valid RD Data IP2Bus_Data IP2Bus_RdAck 0 xip2055 28 www.xilinx.com February 8, 2002 1-800-255-7778 Tutorial: Designing Custom OPB Slave Peripherals for MicroBlaze R PRELIMINARYPRELIMINARYSummary of OPB IPIF Features The above design practice provides an example using the simple register access feature of OPB IPIF. The full outline of OPB IPIF features is summarized below. Users can refer to the OPB IPIF Architecture Specification for more details, including the functional descriptions, design parameters, interface signals and timing diagrams. • Synchronous operation • Hardware and optional software reset • Freeze signal to facilitate debugging • Interrupt Support • Slave Attachment - Register Interface - SRAM Interface (for IP with SRAM-like interface) - Support for burst transactions (optional) • Master Attachment - Support single and burst transactions - Transaction Qualification interface - Transaction Response interface • Write FIFO - BRAM based - Packet support - IP Status flags: Empty, Almost Empty, Occupancy Count • Read FIFO - BRAM based - Packet support - IP Status flags: Full, Almost Full, Vacancy Count • DMA/Scatter Gather - Multiple channels Figure 17: Write Transaction for IP Interconnect Using Register Access Feature Bus2IP_Clk Bus2IP_RegWrCE(i) Bus2IP_WrReq Valid WR Data BusIP2_Data IP2Bus_RdAck 0 xip2056 February 8, 2002 www.xilinx.com 29 1-800-255-7778 References R - Can be used in conjunction with Read and Write FIFOs - Optional packet capability for SG channels - Optional interrupt coalescing feature for packet SG channels - Uses an IPIF-internal master interface References • MicroBlaze Software Reference Guide • MicroBlaze Hardware Reference Guide • OPB IPIF Architecture Specification • IBM On-Chip Peripheral Bus Architecture Specifications v2.1 Revision History Date Description September 7, 2001 Initial Release February 8, 2002 MDK 2.1 30 www.xilinx.com February 8, 2002 1-800-255-7778 Tutorial: Designing Custom OPB Slave Peripherals for MicroBlaze R
