[fpga-miniconf] litevideo VGA on arty WIP

[Florent Kermarrec]

>
> So, I just need to do something like:
> https://github.com/futaris/litex-buildenv/blob/master/
> targets/nexys_video/video.py#L128
>

Yes you can do that.

>
> Is this the best documentation on how the mmcm & clocking works on
> Artix-7?
> https://www.xilinx.com/support/documentation/user_
> guides/ug472_7Series_Clocking.pdf
>

That's the right document.

>
> HDMI/DVI clocks 10 times faster for the pixels, compared to the main
> clock, right?
>

> VGA clocks once per pixel, so I will probably have to modify that.
>

In both case we are outputing the pixel clock. Just that for HDMI/DVI data
are serialized and use 10b/8b so yes 10 times faster than clock.


> Can I hard code the pixel clock in the gateware, rather than use the pix
> clock?
>

Yes you can, just set the default parameters of this MMCME2_ADV to the
values you want:
https://github.com/enjoy-digital/litevideo/blob/master/litevideo/output/hdmi/s7.py#L100

Florent



> On Mon, Feb 5, 2018, at 6:36 PM, Florent Kermarrec wrote:
>
> Hi Hasjim,
>
> it's strange you don't have at least the clock on the output. First thing
> to check is that your pix clock is working.
> Your changes in the firmware seem fine, but you can try to connect one led
> to a counter clocked by pix_clk to make sure your are configuring the mmcm
> correctly.
>
> Florent
>
> 2018-02-05 1:24 GMT+01:00 Hasjim Williams <hasjim.williams at futaris.org>:
>
>
> Hi Florent,
>
> As I suspected, something is weird with the clocking, and the G0 output
> doesn't appear to changing...
>
> I posted some oscilloscope screenshots on #timvideos.
>
> I'm not sure that I've done the firmware code correctly. I've basically
> taken the HDMI_OUT0 stuff and search/replaced with VGA_OUT0.
>
> I haven't really looked into how the MMCM works, or the PLL on the
> MimasV2, so I'm sure I've messed up something.
>
> Is there any documentation on the simulator / verilator and how to run
> litevideo in it ?
>
>
> Hasjim
>
>
> On Sun, Feb 4, 2018, at 9:16 PM, Florent Kermarrec wrote:
>
> Hi Hasjim,
>
> great, to understand why it's not working yet you can check:
> - that the video pattern if enabled for the vga output in the firmware.
> - that you are using a correct video mode (you can start with a low
> resolution)
> - if you have a scope, have a look at the clk/vsync/hsync.
>
> Florent
>
> 2018-02-04 9:35 GMT+01:00 Hasjim Williams <hasjim.williams at futaris.org>:
>
>
> HI everyone,
>
> I managed to get Vivado 2016.4 to output VGA with the Pmod-VGA example
> from:
>
> https://reference.digilentinc.com/reference/pmod/pmodvga/start
>
> https://github.com/Digilent/Arty-Pmod-VGA
> https://reference.digilentinc.com/learn/programmable-logic/t
> utorials/arty-pmod-vga-demo/start
>
> I made some changes to litex-buildenv with the help of Florent, and made a
> pull request on github:
>
> https://github.com/timvideos/litex-buildenv/pull/20
>
> This is still WIP and output doesn't work on Pmod-VGA yet in the hdmi2usb
> firmware.
>
> I don't think it's clocking out the pixel clock, hsync and/or vsync
> correctly yet.
>
> Hasjim 'futaris' Williams
>
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