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rp2pio: Enable read and read/write transactions #4173

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rp2pio: Enable read and read/write transactions #4173

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@jepler
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@jepler jepler commented Feb 10, 2021 •
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Here's my test program, with a workaround for adafruit/Adafruit_CircuitPython_PIOASM#7 applied:

import adafruit_pioasm
import rp2pio
import board
import time

spi_cpha0_source = """
.program spi_cpha0
.side_set 1

.wrap_target
    out pins, 1 side 0 [1] ; Stall here on empty (sideset proceeds even if
    in pins,  1 side 1 [1] ; instruction stalls, so we stall with SCK low)
.wrap

"""

spi_cpha0_assembled = adafruit_pioasm.assemble(spi_cpha0_source)

pio_spi_sm = rp2pio.StateMachine(
    spi_cpha0_assembled,
    frequency=8000000,  # 2 MHz, / 4 (?) clocks per bit
    init=adafruit_pioasm.assemble("set pindirs 3"),
    first_sideset_pin=board.GP1,
    first_out_pin=board.GP0,
    first_in_pin=board.GP2,
    first_set_pin=board.GP0,
    set_pin_count=3,
    auto_pull=True,
    auto_push=True,
    out_shift_right=True,
    in_shift_right=True,
    pull_threshold=8,
    push_threshold=8,
)

print(dir(pio_spi_sm))
b = bytearray(4)
while True:
    b[0] = b[2] = 0xaa
    b[1] = b[3] = 0x55
    print(b, end=" -> ")
    pio_spi_sm.write_readinto(b, b)
    print(b)

I get pulses out on GP0/1 and if I connect GP0 to GP2 I read back the same value I write.

@jepler
WIP: rp2pio: Enable read and read/write transactions
f460e74 
This doesn't actually work for me (adapting the duplex spi example),
though I think the problem lies either with my pio code or the construction
of the StateMachine.
@tannewt
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tannewt commented Feb 10, 2021

We don't automatically set the pin direction for the output pins so you need init code to do it. Your current init uses the set instruction to do it but doesn't provide the first set pin (should be the same as output.)

We probably should automatically set the sideset direction automatically, otherwise we need to use set for it as well.

@jepler jepler changed the title WIP: rp2pio: Enable read and read/write transactions rp2pio: Enable read and read/write transactions Feb 12, 2021
@jepler
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jepler commented Feb 12, 2021

@tannewt I know you have similar code. If you want to take yours in favor of mine (if so feel free to close this up!), make sure you have the equivalent of this change for getting the right shifted-in bits:

     if (rx) {
-        rx_source = (const volatile uint8_t*) &self->pio->rxf[self->state_machine];
-        if (!self->in_shift_right) {
+        rx_source = (volatile uint8_t*) &self->pio->rxf[self->state_machine];
+        if (self->in_shift_right) {
             rx_source += 3;
         }
     }

@tannewt
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tannewt commented Feb 12, 2021

Ok, I deleted the ! which I think is the only change.

@jepler jepler closed this Feb 12, 2021
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@jepler @tannewt