Help in Verilog coding strongly needed

[YangZ]

Help in Verilog coding

Hey Guyz!

I need some help with verilog coding. i got this code off opencore website that teaches us how to code a sd card controller.Below shows 2 of the verilog file.

A) spiMaster_defines.v
`ifdef SIM_COMPILE
`define SD_INIT_START_SEQ_LEN 8'h03
`define MAX_8_BIT 8'h08
`else
`define SD_INIT_START_SEQ_LEN 8'ha0
`define MAX_8_BIT 8'hff
`endif

B) initSD.v
`include "spiMaster_defines.v"
`CLK_SEQ_CHK_FIN:
begin
next_txDataWen <= 1'b0;
if (loopCnt == `SD_INIT_START_SEQ_LEN)
begin
NextState_initSDSt <= `CLK_SEQ_WT_DATA_EMPTY;
end
else
begin
NextState_initSDSt <= `CLK_SEQ_SEND_FF;
end
end

My question is what is the value of `SD_INIT_START_SEQ_LEN ?? Also what is the verilog code in A trying to do? Hope someone can help me as i really need to understand this. Thank you.

 

[devas]

Re: Help in Verilog coding

Hi,

The value of SD_INIT_START_SEQ_LEN depends on the value of SIM_COMPILE. When SIM_COMPILE is 1, SD_INIT_START_SEQ_LEN has the value 3, otherwise a0. Looking at the name, for synthesis the value is a0. I guess this mechanism is used to shorten the simulation time. When there is documentation available you should find it somewhere in it.

The file spiMaster_defines.v is a so called include file. In this file you can define default values. In this case the default values depends on another variable to create a flexible design.

Devas

 

[YangZ]

Help in Verilog coding

Hey Devas,

Thanks a lot for your quick reply. Appreciate it. Btw, what do you mean by "In this case the default values depends on another variable to create a flexible design." Would be great if you could explain in a bit detail. Thanks.

 

[devas]

Re: Help in Verilog coding

Hi,

In an include file you can declare default values simple e.g.:

`define X 8

You can also declare these default values depending on another value as in your example e.g.:

`ifdef SIM
`define X 8
`else
`define X 4
`endif

When the value of SIM is 1 then X will be set to 8. When the value of SIM is 0 than X will be set to 4, so the value of X depends on the value of SIM. This is for example used to set different values during simulation and during synthesis. For example during simulation you set SIM to 1 and when you synthesis your design you set SIM to 0.

Devas

 

[YangZ]

Hey Devas,

Thanks for your help. I understand now. =]

 

[abh_z]

can anyone plz explain the SD controller code in detail?