Something I've wondered about:
>
> Suppose we have a c program running on some little uP, and it has some
> integer variable value, 8 or 12 bits or something, and wants to drive
> a parallel DAC off-chip.
>
> The msb...lsb bits of the variable obviously have to get to the right
> pins of the DAC.
>
> So, in general, how does one pick the physical i/o port pins on the
> uP, to get the order right? The PCB layout is easiest if we just wire
> the DAC to the handiest port pins.
>
> One could test and bit-bang each bit and port individually, and then
> strobe the DAC, but that's inelegant.
>
> In the RP2040 chip, one can apparently write to a register in a
> PIO/state machine block, where each bit of the register can be
> assigned to drive a physical port pin. I think there are some
> constraints on the selected pins.
>
>
>
I didn’t know that now exists - but sounds super useful. Would have saved much headache if it had been around years ago.