DMA Broken Up on MPC8248

I am running Linux 2.4 on an MPC8248. In my code, I do many chaining DMAs with chains consisting of a single segment descriptor. Each segment descriptor has a valid source and destination physical address. The byte count = 0x60 and the next descriptor = 1. The DMAs seem to work as expected, i.e., the 0x60 bytes are successfully transferred from the given sources to the given destinations, but, when I look at the logic analyzer, rather than seeing single DMAs of 0x60 bytes, I see

6 separate DMAs of 0x10 bytes where there should be a single DMA of 0x60 bytes. Shouldn't it DMA 0x60 bytes in one single DMA transfer?
Reply to
Bill
Loading thread data ...

I do not know the 8248, but I remember on the 8240 I tried to use the DMA to move memory to memory. It worked, only several times slower than when I did it using the CPU, so I abandoned it. I did not bother to look into why it was so slow, it obviously not going to get me anywhere so I did tweak the CPU move code as far as I could and am happy ever since :-).

Dimiter

------------------------------------------------------ Dimiter Popoff Transgalactic Instruments

formatting link

------------------------------------------------------

Bill wrote:

Reply to
Didi

Play with the following parameters: BUF_INV,SS_MAX,STS,DTS.

Dimiter, Unlike the mpc8240, where the DMA was implemented in H/W, the mpc8248 IDMA is CPM microcode based. This suggests that the PQx-IDMA is more sophisticated, and can be fine tuned to specific requirements.

David Gabbay DoGav Systems

Reply to
dg

Play with the following parameters: BUF_INV,SS_MAX,STS,DTS.

Dimiter, Unlike the mpc8240, where the DMA was implemented in H/W, the mpc8248 IDMA is CPM microcode based. This suggests that the PQx-IDMA is more sophisticated, and can be fine tuned to specific requirements.

David Gabbay DoGav Systems

Reply to
dg

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.