Pi Pico push seems to truncate value at 5 bits

[sgall17]

The following clip is very basic but as far as I can see is giving the wrong result. Where am I going wrong?

I wanted to implement a tachometer by decrementing X until a pin goes HIGH. I thought I could get the X value out by just moving X into ISR then pushing it. As below:.....

Frequency in statemachine doesnt matter and other values I have left at defaults which I think should be OK.

I have used sm.exec so I can try lots of different values.

Code: Select all

import rp2

code]@rp2.asm_pio()
def prog():
   # set(x,63)
    mov(isr,x)
    push()


sm = rp2.StateMachine(0, prog, freq=4000)
sm.active(1)

for a in range(50):
    sm.exec("set(x,%s)" % a)
    print (sm.get())
    
sm.active(0)

The result is as below:

0
1
2
...

29
30
31
0
1
...
10
11
12

It seems that only the 5 least significant digits are being returned?
What I have done wrong?

[GerryKeely]

Using set x you are limited to a 5 bit no. ie max value 31.
See the RP2040 data sheet section 3.4.10
To load a full 32 bit no. you have to load x(or y) using the ISR or OSR.
eg
mov(x,osr)
label("loop1")
jmp(x_dec,"loop1")

put(value) can be used to load the osr with a full 32 bit no.

regards
Gerry

[sgall17]

Thanks very much - I can see that now. I just assumed loading a register with an immediate value was like normal assembler.