Subj : Re: uP port mapping
To   : john larkin
From : Theo
Date : Thu Sep 12 2024 22:28:42

XPost: sci.electronics.design

In comp.sys.raspberry-pi john larkin <jl@650pot.com> wrote:
> RP2040 has I think 2 PIO blocks and each has a couple of hardware
> programmable state machines, and those can be set up to drive pins.
> I'm mostly concerned now with a PCB schematic design, picking the
> appropriate and easy-to-route pins from the CPU to things.
>
> My general question, for various processors, is how to associate bits
> in integer variables with physical pins on the chip.

This is the function of a 'pinmux'.  Different chips have different
capabilities of the pinmux, but it's rare to be able to connect any GPIO to
any pin - that's more FPGA territory.  Typically the pinmux is just about
selecting one of multiple fixed functions for a given pin
(SPI1_MISO/I2C3_SDA/UART2_TX/...)

So either you route your DAC to consecutive pins (D0 to GPIOn, D1 to n+1,
...., ideally where n is a multiple of 8), or you're prepared to do the
necessary bit shuffling in software (which can be slow and non-atomic).  I'd
suggest sticking to consecutive ordering if you can.

(although I have no experience of the RP2xxx GPIO/PIO shenanigans)

Theo

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