Re: cobalt & dma

[Hans Verkuil <hverkuil@xs4all.nl>]

On 11/17/15 14:15, Ran Shalit wrote:
> On Tue, Nov 17, 2015 at 9:53 AM, Hans Verkuil <hverkuil@xs4all.nl> wrote:
>> On 11/17/2015 08:39 AM, Ran Shalit wrote:
>>> Hello,
>>>
>>> I intend to use cobalt driver as a refence for new pci v4l2 driver,
>>> which is required to use several input simultaneously. for this cobalt
>>> seems like a best starting point.
>>> read/write streaming will probably be suffecient (at least for the
>>> dirst debugging).
>>> The configuration in my cast is i7 core <-- pci ---> fpga.
>>> I see that the dma implementation is quite complex, and would like to
>>> ask for some tips regarding the following points related to dma issue:
>>>
>>> 1. Is it possible to do the read/write without dma (for debug as start) ?
>>
>> No. All video capture/output devices all use DMA since it would be prohibitively
>> expensive for the CPU to do otherwise. So just dig in and implement it.
>>
> 
> Hi,
> 
> Is the cobalt or other pci v4l device have the chip datasheet
> available so that we can do a reverse engineering and gain more
> understanding about the register read/write for the dma transactions ?
> I made a search but it seems that the PCIe chip datasheet for these
> devices is not available anywhere.

Sorry, no, it's not publicly available.

But they all work along the same lines: each DMA descriptor has a
PCI DMA address (where the data should be written to in memory), the length
(bytes) of the DMA transfer and the pointer to the next DMA descriptor (chaining
descriptors together). Finally there is some bit to trigger and interrupt when
the full frame has been transferred.

Regards,

	Hans