[J-core] HDMI

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Why did you chose HDMI and not DisplayPort?

DisplayPort is an open standard created by VESA. It is even able to
transport HDMI signals if you really need HDMI. With HDMI I have to use
a proprietary format on an otherwise fully open specification processor.

kind regards
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On 19/10/16 08:15, Rob Landley wrote:
> On 10/18/2016 06:57 PM, Rich Felker wrote:
>> On Tue, Oct 18, 2016 at 05:59:04PM -0500, BGB wrote:
>>>>> my thought here is that the 250MHz needed to pull off HDMI output may be out
>>>>> of reach for lower end FPGA's, but I am not sure.
>>>> Why do you think we need 250Mhz ? For the lower pixels format, aka
>>>> 640*480 @60Hz, we only seems to need 25Mhz. Is there something I
>>>> missed ? Also the turtle will only come with an HDMI output, like the
>>>> RPi do.
>>>
>>> 25MHz is the pixel-rate, but the pixels need to be sent as a serial
>>> stream of bits; this pushes the required bitrate up *considerably*,
>>> and you would end up needing to drive 250MHz on the output pins (and
>>> for serial parts of the interface).
>>>
>>> contrast with the analog interfaces, one doesn't need to send nearly
>>> as many bits, and the bits don't need to get through reliably; it is
>>> more just the faster the DPWM is, the higher the output image
>>> quality can be (one might only need a few bits per pixel to get
>>> "acceptable" output).
>>
>> I don't think there's any need for concern here. My understanding is
>> that Jeff has already tested HDMI output via a simple pattern
>> generator bitstream and it works fine. Scanning out a framebuffer
>> should not be any harder to meet timing for; AFAIK the plan is to have
>> a small local buffer that fills via DMA, and output bits from this
>> buffer at the HDMI video clock.
> 
> Jeff posted the example code he used, attached to this message:
> 
> http://lists.j-core.org/pipermail/j-core/2016-August/000341.html
> 
> Rob
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