FIFO Works fine on EDAPlayground but not Quartus

[Altera_Forum]

All, 

The following code works fine and as expected on EDAPlayground, but Quartus has an issue with it. I get the ERROR 10028 Can't resolve multiple constant drivers for nets w_addr and r_addr.  I am treating w_addr and r_addr as a temporary variable that can have a value 0 to 31, (5-bits)  Any ideas? Thanks, Keith   ////////////////////////////////////////////////////////////////////// //================================================================ // FIFO test in an array specfic for HiDS // set up for Dual clocks // one to Write // one to Read // also will need to have 2 data busses // Data IN // Data OUT // Extras // nReset -- CLR on LO // Empty -- HI indicates empty module DFIFO_array(D_Out, Empty, D_In, wrclk, rdclk, nrst); output D_Out; //output D_Out; output Empty; reg D_Out; //reg D_Out; input D_In; //input D_In; input wrclk; input rdclk; input nrst; // // DFIFO for 64 Channel SAM 41 x 32 // EFIFO for 64 Channel SAM 10 x 64 parameter WIDE = 41; parameter DEEP = 32; // this should give us a FIFO of 41 bits Wide by 32 words deep // 9-bit counter in MSB bits 32:41 // 32-bit channel representation in 0:31 // // reg addr; //reg addr; reg w_addr; reg r_addr; always @ (posedge wrclk) begin addr <= D_In; w_addr <= w_addr + 1; end always @ (posedge rdclk) begin r_addr <= r_addr + 1; D_Out <= addr; end always @ (nrst) begin if (!nrst) begin w_addr <= 0; r_addr <= 0; end end assign Empty = (w_addr == r_addr); endmodule /////////////////////////////////////////////////////////////

[Altera_Forum]

--- Quote Start ---  All, The following code works fine and as expected on EDAPlayground, but Quartus has an issue with it. I get the ERROR 10028 Can't resolve multiple constant drivers for nets w_addr and r_addr.  I am treating w_addr and r_addr as a temporary variable that can have a value 0 to 31, (5-bits)  Any ideas? Thanks, Keith   ////////////////////////////////////////////////////////////////////// //================================================================ // FIFO test in an array specfic for HiDS // set up for Dual clocks // one to Write // one to Read // also will need to have 2 data busses // Data IN // Data OUT // Extras // nReset -- CLR on LO // Empty -- HI indicates empty module DFIFO_array(D_Out, Empty, D_In, wrclk, rdclk, nrst); output D_Out; //output D_Out; output Empty; reg D_Out; //reg D_Out; input D_In; //input D_In; input wrclk; input rdclk; input nrst; // // DFIFO for 64 Channel SAM 41 x 32 // EFIFO for 64 Channel SAM 10 x 64 parameter WIDE = 41; parameter DEEP = 32; // this should give us a FIFO of 41 bits Wide by 32 words deep // 9-bit counter in MSB bits 32:41 // 32-bit channel representation in 0:31 // // reg addr; //reg addr; reg w_addr; reg r_addr; always @ (posedge wrclk) begin addr <= D_In; w_addr <= w_addr + 1; end always @ (posedge rdclk) begin r_addr <= r_addr + 1; D_Out <= addr; end always @ (nrst) begin if (!nrst) begin w_addr <= 0; r_addr <= 0; end end assign Empty = (w_addr == r_addr); endmodule /////////////////////////////////////////////////////////////  --- Quote End ---    you need to insert the statements: w_addr <= 0; r_addr <= 0;  so as to reset them in same top two processes.

[Altera_Forum]

--- Quote Start ---  you need to insert the statements: w_addr <= 0; r_addr <= 0;  so as to reset them in same top two processes.  --- Quote End ---    I guess I don't understand. If I reset them in each posedge process, then they will always be zero, and the array will not increment. I do set them to zero in my nrst section.  Keith

[Altera_Forum]

--- Quote Start ---  I guess I don't understand. If I reset them in each posedge process, then they will always be zero, and the array will not increment. I do set them to zero in my nrst section.  Keith  --- Quote End ---    Inside each process the assignments are treated as sequential. But each process runs parallel to any other process. So by having separate processes on your same signal you are driving it twice in parallel. This is mutiple driver case and HDL standard is against it and I assume tools should respect it or not.

[Altera_Forum]

You need reset outside (before) clock edge

[Altera_Forum]

This is incorrect semantics for implementing a synchronously clocked register with an asynchronous reset: 

  always @ (posedge rdclk) begin r_addr <= r_addr + 1; D_Out <= addr; end always @ (nrst) begin if (!nrst) begin r_addr <= 0; end end   You need to rewrite the each register as a single always block:   always @ (posedge rdclk or negedge nrst) begin if (!nrst) begin r_addr <= 0; end else begin r_addr <= r_addr + 1; D_Out <= addr; end end