[J-core] How crazy would a nommu debian port be?

Rob Landley rob at landley.net
Sat Aug 20 01:12:41 EDT 2016

On 08/19/2016 11:38 PM, Rich Felker wrote:
> The Turtle has an hdmi port, no vga, though you could put an adapter
> on it if you want. The Numato Mimas v2 board has a vga port, but it
> only has 2/3/2 bits per channel in the dac output, which is pretty
> ugly. You might could remedy this via hardware dithering, i.e. running
> the video clock significantly higher than the actual pixel rate and
> modulating the low bits rapidly to simulate more color depth.
> As far as I know, no work has been done on writing the vhdl for
> driving either of them, but I think the bulk of the work is the
> controller that receives samples over dma and buffers them for output,
> and that's shareable between boards with hdmi output and vga output.

I was in Japan when the turtle board prototypes came in, and I saw Jeff
grab an HDMI demo off the net and stick it in a turtle board to make a
pretty test pattern we could see on a monitor, demonstrating that the
HDMI port was wired up properly.

But it wasn't doing DMA from a framebuffer, it was just generating a
pattern based off of a timer and some registers. (And it was verilog
while what we're doing is vhdl, and who knows what the license was. At
the moment the plan to implement the hdmi video support for turtle is
still "write new vhdl code".)

I was under the vague impression numato had some test code for their
vga, but I dunno how useful it is or how you'd glue it to j2. Could be a
similar "generate a test pattern" thing, with the wrong license, in the
wrong language.

On freenode Khem Raj said he got most of xfce running on a nommu system
(cortex-m), so maybe modest desktop isn't an unreasonable target. But
there's missing vhdl to implement the video card on both boards.

> Rich


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