Passing parameters to FPGA

[josuedavila]

Hi,
I'm trying to add a digital filter at the output of the arbitrary signal generator in red pitaya. Currently my filter does something (but not what I expect).
To be able to debug it (and later on for normal operation) I need to pass parameters to the filter to control its behavior, but I'm not sure where to start. Do I write a C program that writes the parameters in some sector of memory? Is there an example that I can use to understand how this works? And, on the FPGA side, how do I tell my filter to read its parameters from a particular region of memory?
Any pointers to relevant information will help
Thanks a lot

[Nils Roos]

Hi,

if you are adding the filter inside the ASG module (fpga/rtl/red_pitaya_asg.v), you can use the already existing mechanisms to pass parameters to the logic.

On the FPGA side you'd define new registers to hold your parameters (eg. here):

Code: Select all

[...]
reg [ 32-1: 0] set_a_rdly , set_b_rdly ;
reg [ 32-1: 0] set_a_myparameter , set_b_myparameter ; // add as many as you need
[...]

Then choose an unused address within the ASG range and create read and write logic to handle it (writing):

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[...]
      if (sys_addr[19:0]==20'h40)  set_b_rdly <= sys_wdata[  32-1: 0] ;
      if (sys_addr[19:0]==20'h100)  set_a_myparameter <= sys_wdata[  32-1: 0] ;
      if (sys_addr[19:0]==20'h104)  set_b_myparameter <= sys_wdata[  32-1: 0] ;
[...]

and (reading):

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[...]
     20'h00040 : begin sys_ack <= sys_en;          sys_rdata <= set_b_rdly                         ; end
     20'h00100 : begin sys_ack <= sys_en;          sys_rdata <= set_a_myparameter                  ; end
     20'h00104 : begin sys_ack <= sys_en;          sys_rdata <= set_b_myparameter                  ; end
[...]

The example parameters would be mapped to the addresses 0x40200100 and 0x40200104.

You can also take the oscilloscope as an example - it has the filter parameters "set_a_filt_.." and "set_b_filt_.." for its internal filters.

On the application side, you use a memory mapped pointer to access the new addresses. Examples can be found in the acquire and generate utilities, and this topic has also been discussed exhaustively in this forum.