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Apr 29, 2025
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Rewrite SerialPIO receive path, ensure proper edge #2929

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Rewrite SerialPIO receive path, ensure proper edge
earlephilhower Apr 28, 2025
c163d4a
Typo
earlephilhower Apr 28, 2025
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12 changes: 4 additions & 8 deletions cores/rp2040/SerialPIO.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -69,7 +69,7 @@ static PIOProgram *_getRxProgram(int bits) {
// ------------------------------------------------------------------------

// TODO - this works, but there must be a faster/better way...
static int _parity(int bits, int data) {
static int __not_in_flash_func(_parity)(int bits, int data) {
int p = 0;
for (int b = 0; b < bits; b++) {
p ^= (data & (1 << b)) ? 1 : 0;
Expand Down Expand Up @@ -98,11 +98,7 @@ void __not_in_flash_func(SerialPIO::_handleIRQ)() {
}
while (!pio_sm_is_rx_fifo_empty(_rxPIO, _rxSM)) {
uint32_t decode = _rxPIO->rxf[_rxSM];
decode >>= 33 - _rxBits;
uint32_t val = 0;
for (int b = 0; b < _bits + 1; b++) {
val |= (decode & (1 << (b * 2))) ? 1 << b : 0;
}
uint32_t val = decode >> (32 - _rxBits - 1);
if (_parity == UART_PARITY_EVEN) {
int p = ::_parity(_bits, val);
int r = (val & (1 << _bits)) ? 1 : 0;
Expand Down Expand Up @@ -234,7 +230,7 @@ void SerialPIO::begin(unsigned long baud, uint16_t config) {
_writer = 0;
_reader = 0;

_rxBits = 2 * (_bits + _stop + (_parity != UART_PARITY_NONE ? 1 : 0) + 1) - 1;
_rxBits = _bits + (_parity != UART_PARITY_NONE ? 1 : 0);
_rxPgm = _getRxProgram(_rxBits);
int off;
if (!_rxPgm->prepare(&_rxPIO, &_rxSM, &off, _rx, 1)) {
Expand All @@ -249,7 +245,7 @@ void SerialPIO::begin(unsigned long baud, uint16_t config) {
pio_sm_clear_fifos(_rxPIO, _rxSM); // Remove any existing data

// Put phase divider into OSR w/o using add'l program memory
pio_sm_put_blocking(_rxPIO, _rxSM, clock_get_hz(clk_sys) / (_baud * 2) - 7 /* insns in PIO halfbit loop */);
pio_sm_put_blocking(_rxPIO, _rxSM, clock_get_hz(clk_sys) / (_baud * 2) - 3);
pio_sm_exec(_rxPIO, _rxSM, pio_encode_pull(false, false));

// Join the TX FIFO to the RX one now that we don't need it
Expand Down
23 changes: 14 additions & 9 deletions cores/rp2040/pio_uart.pio
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Expand Up @@ -73,20 +73,25 @@ static inline void pio_tx_program_init(PIO pio, uint sm, uint offset, uint pin_t
; IN pin 0 and JMP pin are both mapped to the GPIO used as UART RX.

start:
set x, 18 ; Preload bit counter...we'll shift in the start bit and stop bit, and each bit will be double-recorded (to be fixed by RP2040 code)
set x, 18 ; Preload bit counter...overwritten by the app
wait 0 pin 0 ; Stall until start bit is asserted

bitloop:
; Delay until 1/2 way into the bit time
mov y, osr
wait_half:
jmp y-- wait_half
wait_mid_start:
jmp y-- wait_mid_start

; Read in the bit
in pins, 1 ; Shift data bit into ISR
jmp x-- bitloop ; Loop all bits

push ; Stuff it and wait for next start
bitloop:
mov y, osr
bitloop1:
jmp y-- bitloop1
mov y, osr
bitloop2:
jmp y-- bitloop2

in pins, 1
jmp x-- bitloop
push

% c-sdk {
static inline void pio_rx_program_init(PIO pio, uint sm, uint offset, uint pin) {
Expand Down
14 changes: 9 additions & 5 deletions cores/rp2040/pio_uart.pio.h
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Expand Up @@ -71,7 +71,7 @@ static inline void pio_tx_program_init(PIO pio, uint sm, uint offset, uint pin_t
// ------ //

#define pio_rx_wrap_target 0
#define pio_rx_wrap 6
#define pio_rx_wrap 10
#define pio_rx_pio_version 0

static const uint16_t pio_rx_program_instructions[] = {
Expand All @@ -80,16 +80,20 @@ static const uint16_t pio_rx_program_instructions[] = {
0x2020, // 1: wait 0 pin, 0
0xa047, // 2: mov y, osr
0x0083, // 3: jmp y--, 3
0x4001, // 4: in pins, 1
0x0042, // 5: jmp x--, 2
0x8020, // 6: push block
0xa047, // 4: mov y, osr
0x0085, // 5: jmp y--, 5
0xa047, // 6: mov y, osr
0x0087, // 7: jmp y--, 7
0x4001, // 8: in pins, 1
0x0044, // 9: jmp x--, 4
0x8020, // 10: push block
// .wrap
};

#if !PICO_NO_HARDWARE
static const struct pio_program pio_rx_program = {
.instructions = pio_rx_program_instructions,
.length = 7,
.length = 11,
.origin = -1,
.pio_version = 0,
#if PICO_PIO_VERSION > 0
Expand Down