P-SeriesのトピックRe: PCI Express Read Burst Transaction

PCI Express Read Burst Transaction

michayardeny — Thu, 08 Jun 2017 05:21:19 GMT

Question regarding initiate burst PCI Express transaction from Host CPU .(Using p1022).

As far as I understand CPU access to PCI memory will end-up in a 32bit or 64bit PCIE transfer requests.

Is it possible to create a read transaction of more then 64 bit (that will be implemented in one burst on the PCI Express)?

Is it possible to accomplish that with the DMA Controller where source address will point to a PCIE memory space?

Micha

Re: PCI Express Read Burst Transaction

ufedor — Thu, 08 Jun 2017 05:34:22 GMT

Your understanding is correct - it is possible to initiate PCIe transfers having data payload more than 64 bytes using DMA.

Re: PCI Express Read Burst Transaction

michayardeny — Wed, 02 Aug 2017 09:26:10 GMT

Basically We have now that DMA working fine with 128 bytes payloads above PCI-E .

Can we theoretically increase DMA transfer size beyond the MPS (Maximum Payload Size)

Or in other works my question is can the host splits DMA transection to smaller TLP packets ?

If the answer is negative is that possible to go around it with limiting DMA band width BWC.?

Re: PCI Express Read Burst Transaction

ufedor — Wed, 02 Aug 2017 10:13:40 GMT

The split size in the described case is equal to the BWC (if BWC is less or equal to negotiated payload size).

Re: PCI Express Read Burst Transaction

michayardeny — Wed, 02 Aug 2017 12:28:24 GMT

Thanks and if BWC is disabled would the DMA split the transaction to maximum payload size TLP's?

Re: PCI Express Read Burst Transaction

ufedor — Wed, 02 Aug 2017 12:35:22 GMT

Correct.

Re: PCI Express Read Burst Transaction

brett_p_stahlma — Sat, 14 Jul 2018 02:04:06 GMT

@ufedor @Micha_Yardeny

I'm using an LS1012A as an Endpoint and need to read large amounts of data from an RC. Performing memory-mapped reads using the core is working but extremely slow. I assume this is because the MRd TLPs are very small. Can you point me to any code examples showing the use of eDMA with PCIe, or even just a basic overview of how to achieve burst transactions?

Thanks,

Brett S.