PCI 0 - Simple PCI interface
This is an example of PCI code.
We control an LED using PCI write commands.
Writing a "0" turns the LED off, writing a "1" turns the LED on!
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// Very simple PCI target // Just 3 flip-flops for the PCI logic, plus one to hold the state of an LED module PCI(CLK, RSTn, FRAMEn, AD, CBE, IRDYn, TRDYn, DEVSELn, LED); input CLK, RSTn, FRAMEn, IRDYn; input [31:0] AD; input [3:0] CBE; inout TRDYn, DEVSELn; output LED; parameter IO_address = 32'h00000200; // we respond to an "IO write" at this address parameter CBECD_IOWrite = 4'b0011; //////////////////////////////////////////////////// reg Transaction; wire TransactionStart = ~Transaction & ~FRAMEn; wire TransactionEnd = Transaction & FRAMEn & IRDYn; wire Targeted = TransactionStart & (AD==IO_address) & (CBE==CBECD_IOWrite); wire LastDataTransfer = FRAMEn & ~IRDYn & ~TRDYn; always @(posedge CLK or negedge RSTn) if(~RSTn) Transaction <= 0; else case(Transaction) 1'b0: Transaction <= TransactionStart; 1'b1: Transaction <= ~TransactionEnd; endcase reg DevSelOE; always @(posedge CLK or negedge RSTn) if(~RSTn) DevSelOE <= 0; else case(Transaction) 1'b0: DevSelOE <= Targeted; 1'b1: if(TransactionEnd) DevSelOE <= 1'b0; endcase reg DevSel; always @(posedge CLK or negedge RSTn) if(~RSTn) DevSel <= 0; else case(Transaction) 1'b0: DevSel <= Targeted; 1'b1: DevSel <= DevSel & ~LastDataTransfer; endcase assign DEVSELn = DevSelOE ? ~DevSel : 1'bZ; assign TRDYn = DevSelOE ? ~DevSel : 1'bZ; wire DataTransfer = DevSel & ~IRDYn & ~TRDYn; reg LED; always @(posedge CLK) if(DataTransfer) LED <= AD[0]; endmodule |