Factor out resource "sevenseg".

cr1901 commented 5 years ago

Differences between various 7SDs:

Common cathode vs anode?
Is decimal point used?
Are the digit enable signals one-hot coming out of the FPGA or not?
- Using a single enable line, where 0 controls one digit, and 1 controls the other seems more common when only two digits are present (fairly common setup). Otherwise, one-hot is used.

Potential `Subsignal` naming scheme:

a, b, ... g, dp for decimal point (if present)
en{0, 1, 2}
- How should one-hot vs shared en be handled in naming. Should there be a difference?

Boards using it right now

None! But Mercury will (for the baseboard peripheral that is normally attached to it), and in omigen, the naming scheme was inconsistent. So I want to fix this before it becomes a problem.

mithro commented 5 years ago

BTW 7-segment displays are a common learning exercise for beginner HDL coders. It would be good to have good support for them and to not make it too easy....

cr1901 commented 5 years ago

BTW 7-segment displays are a common learning exercise for beginner HDL coders. It would be good to have good support for them and to not make it too easy....

I'm assuming we've left the realm of "not make it too easy" for beginners once PinsN was introduced. For "NMigen for beginners" literature, I'm guessing "active-high" and "active-low" will need to be footnotes. Similar w/ seven seg quirks.

whitequark commented 5 years ago

Common cathode vs anode?

Logical high means LED is lit.

Is decimal point used?

Optional, the downstream code can check it with hasattr(seven_seg, "dp").

Are the digit enable signals one-hot coming out of the FPGA or not?

The enable signal is called sel if it's straight binary, and en if it's one-hot. (No enable signal is also OK for one digit.

I'm assuming we've left the realm of "not make it too easy" for beginners once PinsN was introduced.

Yes.

m-labs / nmigen-boards