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From: The Natural Philosopher <tnp@invalid.invalid>
Newsgroups: sci.electronics.design,comp.sys.raspberry-pi
Subject: Re: uP port mapping
Date: Fri, 13 Sep 2024 09:36:31 +0100
Organization: A little, after lunch
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On 12/09/2024 22:28, Theo wrote:
> 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/...)
> 
That is my understanding, too.  What the pins do is programmable, but 
not tire mappings to specific registers  inside the processor

> 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.
> 
Yes.

> (although I have no experience of the RP2xxx GPIO/PIO shenanigans)
> 
I have - a very very little - but I have spent some time reading the 
docs to see at least if the Pi PICO is suitable for various speculative 
projects or not.

There is a massive amount of shit it *can* do that probably only one 
person in a hundred would ever use.

It just so happens that driving parallel connected external logic is 
something I have an interest in, so I read that bit... :-)

> Theo

-- 
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