Re: cobalt & dma

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On Tue, Nov 17, 2015 at 3:54 PM, Hans Verkuil <hverkuil@xxxxxxxxx> wrote:
> On 11/17/15 14:15, Ran Shalit wrote:
>> On Tue, Nov 17, 2015 at 9:53 AM, Hans Verkuil <hverkuil@xxxxxxxxx> 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.
>


Thank you all very much for all these valuable information !
I must admit that when I observe the source examples,
it seems quite complex, (at least much more complex than the driver I
am familiar with, which most of them time is taking a functional
example and understanding what to change and how, or writing simple
drivers.... )

If there are any other tips and ideas about debug/testing/development
steps when doing pci v4l device driver please tell me.

Thank you all very much,
Ran
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