[J-core] Simple introductory project - Numato board 7-segment display

[Forest Crossman]

I wrote some Verilog to do this a while back--the code is here:
https://github.com/cyrozap/mimas_v2_hex_display

With the default refresh rate of 1 kHz, there is no visible flickering
and it easily meets timing constraints. Also, it's been a while since
I last built anything with it, but I believe the LUT usage is below
100 or so.

I only wanted to display unsigned bytes as hex so this isn't a full
general-purpose driver, but modifying it to individually address each
segment of each display shouldn't be too difficult.

On Wed, Oct 12, 2016 at 1:12 PM, Rich Felker <dalias at libc.org> wrote:
> While debugging some actual work on the Numato Mimas v2 board, I
> happened to look up how the 7-segment leds work. Their usefulness is
> limited by the fact that there are only 8 actual gpio pins controlling
> the segments for all 3, along with an enable pin for each digit,
> meaning each digit has to be off or displaying the same content as the
> other active digits.
>
> In principle it should be possible to add a small bit of vhdl that's
> clocked to cycle which digit is enabled, reading from a 12 bit
> register storing the desired contents for all three. In many ways this
> is like primitive video scan (like what you'd do for vga) and would be
> a both a good exercise for getting started on that type of design with
> immediate results, and a useful tool to have around for debugging.
>
> Rich
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-- 
Forest Crossman