Re: PCIe problem with large TLPs

Altera_Forum · ‎11-08-2011

I'm sending a TLP (from the application layer) of 4 headers and 128 bits of data (Avalon-TX 128).

Headers look like this:

header0 = 32'h60000004; //fmt = 3, length = 4 DW

header1 = 32'h000000FF; //first BE = F, last BE = F

header2 = 32'h00000000;

header3 = address; //that is 32-bit wide

Afterwars I send it like this:

tx_valid_next = 1;

tx_data_next = {header3, header2, header1, header0};

tx_sop_next = 1;

Next cycle: sending the data

tx_sop_next = 0;

tx_valid_next = 1;

tx_data_next = data; //that is 128-bit wide

tx_eop_next = 1;

Next cycle: deasserting eop and valid. Also checking TX_ready before asserting TX_valid.

problem:

When I use shmem_display, it shows all zeros, whereas it all works fine with the code like this:

//3 DW headers, 32-bit data payload, single transaction

header0 = 32'h40000001;

header1 = 32'h0000000F;

header2 = address;

tx_valid_next = 1;

tx_data_next = {data, header2, header1, header0};

tx_sop_next = 1;

tx_eop_next = 1;

What am I missing?

Altera_Forum · ‎11-09-2011

The PCIe spec says:

--- Quote Start ---

• For Addresses below 4 GB, Requesters must use the 32-bit format.

--- Quote End ---

So, in your TLP generator you have to check the upper 32 bits of the address to be zero and use a 3 word TLP in this case.

Altera_Forum · ‎11-10-2011

It worked with 3DW headers! Thanks!