RP2040 Micropython PIO - Part 1 - Blinking nop, jmp, and .side experiments!

 I'm working on incrementally adding complexity to PIO programs to learn how to use them.  Here are a few examples.  Note that I'm using Pin 6 for the LED on the Arduino Connect Nano RP2040 board.  I think the pin is different for the Pi Pico.

Most Simple Blinking the LED:

The most simple classic blinking example - toggle a pin on and off with the slowest freqency (2000) and a bunch of nop waits to slow the blinking down enough that we can see it!

@rp2.asm_pio(set_init=rp2.PIO.OUT_LOW)

def blink():

wrap_target()

set(pins, 1) [31]

nop() [31]

nop() [31]

nop() [31]

nop() [31]

set(pins, 0) [31]

nop() [31]

nop() [31]

nop() [31]

nop() [31]

wrap()

# sm = rp2.StateMachine(0, pio_junk.blink, freq=2000, set_base=Pin(6))

# sm.active(1)

Blinking the LED Using sideset and jmp for more nop:

In this example, we use sideset to toggle the LED pin on and off and jmp to loop for more nop.

Normally, in each PIO assembled instruction, 5 bits are available to specify length of wait, so 0-31 wait cycles.  But when we enable sideset, 2 (or more??) bits are used to specify the sideset value.  In this case, we use Pin 6 (the LED) as the sideset pin, and we have a max wait of 7 (three bits). 

This speeds up the program execution without a bunch more nop calls.  So we can count on the x scratch register to repeatedly call nop with a jmp and slow the blinking enough that we can see it, like before using sideset and the longer [31] wait.

@rp2.asm_pio(sideset_init=rp2.PIO.OUT_LOW)

def side_blink():

wrap_target()

set(x, 31).side(0x0)

label("aloop")

nop() [7]

jmp(x_dec, "aloop")

set(x, 31).side(0x1)

label("bloop")

nop() [7]

jmp(x_dec, "bloop")

wrap()

# sm = rp2.StateMachine(0, pio_junk.side_blink, freq=2000, sideset_base=Pin(6))

# sm.active(1)

Up next...

I'm trying to read the value of all of the pins and put the values into the fifo to be used by the Micropython program...