pico analog read issue/stability

Thanks - yes, it does look bad. Just looked at this and it seems to be a problem with the STM32's cache grabbing more data while reading from analog.

Try poke32(0x40023C00, peek32(0x40023C00)&~256); - you'll have to do it on onInit if you want it to stay working between power cycles - it disables prefetch.

For instance, with B1 shorted to 3.3v:

function test(pin) {
  var a = new Uint16Array(1000);
  var mean = 0;
  for (var i=0;i<a.length;i++) {
    a[i] = analogRead(pin)*4096;
    mean += a[i];
  }
  mean /= a.length;
  print("Mean: "+mean);
  var variance = 0;
  for (var i=0;i<a.length;i++) {
    var d = a[i]-mean;
    variance += d*d;
  }
  variance /= a.length;  
  print("Variance: "+variance);
}

poke32(0x40023C00, peek32(0x40023C00)|256);
console.log("With prefetch");
test(B1);
poke32(0x40023C00, peek32(0x40023C00)&~256);
console.log("Without prefetch");
test(B1);

//With prefetch
//Mean: 4080.495
//Variance: 309.49997499999
//Without prefetch
//Mean: 4091.12
//Variance: 49.1316

So yeah, massive difference. I need to see how it affects performance before I put it in the actual firmware - I guess it's possible it could just be disabled while doing the analog read, but I wonder whether that would be good enough.