Raspberry Pico MicroPython: Sampling ADC with trigger and Register Peek and Poke using Inline Assembler

[cebersp]

Hi,
perhaps this might be useful for someone. It provides peek and poke to hardware registers and it provides sampling at the adc0.
It samples into a buffer at a given sample frequency, up to 500.000 samples/sec.
As written in the rp2040 datasheet, to use the adc inputs, digital io must be switched off first.
It will wait for ever, if the trigger levels will not be reached. At the moment only positive edge is supported.

Enjoy, Christof

Code: Select all

title= "inlineG.py" # http://docs.micropython.org/en/v1.9.3/pyboard/pyboard/tutorial/assembler.html
# by CWE
from rp2 import *
from machine import *
from time import *
import uarray

led= Pin(25,Pin.OUT)
#led(1)
#sleep(0.2)
#led(0)

adc0=ADC(0)

ledData = uarray.array('i',[
                0xd0000000 + 0x010, # 0 SIO OUT
                0xd0000000 + 0x018, # 4 SIO OUT_CLR
                0xd0000000 + 0x014, # 8 SIO OUT_SET
                1<<25 # 12 LED MASK
                ])


@micropython.asm_thumb
def regPeek(r0): # Address
    mov(r1,r0)
    ldr(r0,[r1,0])

@micropython.asm_thumb
def regPoke(r0, r1): # Address, Data
    str(r1,[r0,0])
    mov(r0,r1)
    
def regSet(adress, mask):
    regPoke(adress, regPeek(adress) | mask)


rGPIO26= 0x4001c000+0x6c # S. 312
regPoke( rGPIO26, 1<<7 ) # switch off ADC0 input and output

adcBuf = uarray.array('h',range(0,20)) # 320 signed short



adcCtrl = uarray.array('i',[
    0x4004c000, # BASE 0 CS, 4 Result, 8 FCS, 12 FIFO, 16 DIV S. 570
    1, # 4 Status: 0 done, 1 start
    len(adcBuf), # 8
    1, # 12 trig sign 1= positive
    2048 - 100, # 16 trigLevel
    2048 + 100 # 20 trigger level
    ])



@micropython.asm_thumb
def adcGet(r0, r1): # BufferAddress, Ctrl-Array

    b(Entry)
    #b(StartSample)
    
    label(GetAdc) # get one sample out of the fifo
    ldr(r2,[r1,0])
    ldrh(r2,[r2,10]) # read upper Half of FCS - something in the fifo?
    cmp(r2,0)
    bls(GetAdc)
    ldr(r2,[r1,0])
    ldr(r2,[r2,12]) # read FIFO
    bx(lr)
    
    label(Entry)
    mov(r4,r0) # BufferAdress
    ldr(r3,[r1,16]) # Trigger Level
    mov(r0,r3)

    #cpsid(1)
    bl(GetAdc) # empty fifo
    bl(GetAdc)
    bl(GetAdc)
    bl(GetAdc)
    bl(GetAdc)
    bl(GetAdc)
    
    label(WaitLow)
    bl(GetAdc)
    cmp(r2,r3)
    bgt(WaitLow)

    ldr(r3,[r1,20]) # Upper Trigger Level
    label(WaitHigh)
    bl(GetAdc)
    cmp(r3,r2)
    bgt(WaitHigh)
    
    label(StartSample)
    ldr(r3,[r1,8]) # Buffer Length
    label(GetNext)
    bl(GetAdc)
    strh(r2,[r4,0])
    add(r4,r4,2) # next address
    sub(r3,r3,1)
    cmp(r3,0)
    bhi(GetNext)
    
    #cpsie(1)
    label(End)




print(title)

adc0.read_u16() # set up the channel
maxSample= 48e6 # Hz
fSample= 250_000 # This is the sampling frequency!
div= int(maxSample/fSample)
print("Div:", div)
regPoke(0x4004c000 + 0x10, div<<8) # set DIV register
#print("Div:", "{0:b}".format(regPeek(0x4004c000 + 0x10)))

regSet(0x4004c000 + 0x08, 1) # set fifo enable
#print("CS:", "{0:b}".format(regPeek(0x4004c000 + 0x00)))

regSet(0x4004c000, 1<<3) # set startmany
#print("CS:", "{0:b}".format(regPeek(0x4004c000 + 0x00)))

#while True:
#print(adcGet(adcBuf, adcCtrl))
led(1)
adcGet(adcBuf, adcCtrl)
led(0)
for i in range(0,len(adcBuf)):
    print(adcBuf[i])
     

[tony1tf]

Thanks Christof

I am experimenting with various means of accessing the ADC on the Pico, having discovered its bad differential non-linearity. You code will give me another method.

Tony

[cebersp]

Hi Tony,
did you switch off the digital input first?

This seems to solve the bad linearity:
"rGPIO26= 0x4001c000+0x6c # S. 312
regPoke( rGPIO26, 1<<7 ) # switch off ADC0 input and output
"

Good luck, Christof