Explanation of systemveilog code snippet for SPI

[verif.ier]

The following is a working code snippet for read/write operation using spi protocol to a slave with addr address. Could anyone explain what is the function of the part marked in bold?

task TmspiCmd(bit [13:0] addr, bit rwb=0,inout bit [15:0] data,input bit reg_size=0, input int check =0,input bit[15:0] expData = 0, int tlead =0 );

//..

if(rwb)
      begin
      [B]spiw.data[0] = {2'b00,addr};
      spiw.data[1] = 16'b0;[/B]
      end
    else
      begin
      [B]spiw.data[0] = {2'b10,addr}; 
      spiw.data[1] = data;[/B]
      end

//...

if(rwb)
    begin
      TempData = 0;
      TempData = spiw.resp_data;
      for(int index=0; index <16; index++)
          TempData[index]  =  spiw.resp_data[15-index];
      if (reg_size)
      begin
[B]          if (addr %2)
             data = TempData[15:8];
          else 
             data = TempData[7:0];[/B]
      end
      else 
         [B] data = TempData;[/B]

      `uvm_info("TMSPI:Response=> ",$sformatf("Addr %h  [%h = %h ] [%h]", addr,data,TempData,spiw.resp_data), UVM_LOW);

// ..

 

[ads-ee]

Modulo 2 of the address separates the even and odd addresses, so the bytes can be accessed individually. It would have been easier to understand if they had just done if (addr[0]) instead.

 

[verif.ier]

Thanks for your reply. Yes, I understood odd/even address part but what does it have to do with spi communication?

Also, the following part is confusing to me. How can a 16-bit value be assigned to 1 bit location? Or I am misinterpreting!!!
Again why is it required for spi communication?

spiw.data[0] = {2'b00,addr};
spiw.data[1] = 16'b0;

 

[dave_59]

What is the definition of spiw?

 

[verif.ier]

spiw is declared as follows.

class myBaseTest extends uvm_test;
   SpiCRM spiw

virtual function void build_phase(uvm_phase phase);
   spiw = SpiCRM::type_id::create("slv_wr",this);

I could find defintion of SpiCRM anywhere. May be it is from uvm_test

 

[ads-ee]

You probably need to post the majority of the code as this has a lot of stuff buried in classes, funcitons, etc that will be needed to interpret what the code does.

My thought on your original question about

spiw.data[0] = {2'b00,addr};
spiw.data[1] = 16'b0;

is that the 0 and 1 are not bits but are array indices.

 

[FvM]

I could find defintion of SpiCRM anywhere. May be it is from uvm_test

I think learning how to read code should be your first educational objective. Without knowing the definition of SpiCRM, the discussion is mostly pointless.

It's easy to guess that data is an array of bit vectors, but you should really review the original definition yourself.