XPost: sci.electronics.design   
   From: theom+news@chiark.greenend.org.uk   
      
   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/...)   
      
   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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