topic PCIe bulk transaction without DMA in T-Series

PCIe bulk transaction without DMA

rainerboschung — Thu, 31 Aug 2017 09:45:01 GMT

Question regarding initiate burst PCI Express transaction from Host CPU (T1040).

As far as I understand CPU access to PCI memory will end-up in a 32bit PCIE transfer requests, and for transactions making use of the max payload size of 256B one has to use DMA.

Since the device I have to read from does not support DMA I would like to know whether it is possible to create a single read transaction making use of the full payload size of 256B without using DMA.

Regards

Rainer

Re: PCIe bulk transaction without DMA

lwn — Thu, 14 Sep 2017 18:18:59 GMT

well, you could just use your CPU's DMA engine to do a mem2mem transfer that copies a block of memory between the pcie device BAR0 and system memory. This way your pcie device doesn't need to support DMA by itself.

Re: PCIe bulk transaction without DMA

rainerboschung — Fri, 15 Sep 2017 08:51:08 GMT

Thanks for your answer! Sounds promising.

Does this also work for other than BAR0?

Could you point me to some example code?

Re: PCIe bulk transaction without DMA

lwn — Fri, 15 Sep 2017 10:16:08 GMT

the pcie registers you want to DMA need to be "memory mapped", so any mapped BAR will do

example code depends on your OS -> google it, you are certainly not the first one to do that

Re: PCIe bulk transaction without DMA

SaLaManDer99 — Thu, 09 Nov 2023 06:49:19 GMT

so will this method work for write? and is it working for read?