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   XPost: sci.electronics.design   
      
   On 12/09/2024 22:28, Theo wrote:   
   > In comp.sys.raspberry-pi john larkin  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   
      
   --   
   Civilization exists by geological consent, subject to change without notice.   
     – Will Durant   
      
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