suart_tx.pio

.program suart_tx
.side_set 1 opt
; An 8n1 UART transmit program.
; SET & OUT pins should be set to TX
    set pindirs, 1
.wrap_target
    nop        side 1 [7]  ; Ensure 3 stop bits
    nop               [7]  ; 
    pull              [7]  ; Stall in idle state after 3 stop bits
    set x, 7   side 0 [7]  ; Preload bit counter, assert start bit for 8 clocks
bitloop:                   ; This loop will run 8 times (8n1 UART)
    out pins, 1            ; Shift 1 bit from OSR to the first OUT pin
    jmp x-- bitloop   [6]  ; Each loop iteration is 8 cycles.
.wrap

% c-sdk {
#include "hardware/clocks.h"

static inline int __time_critical_func(suart_tx_program_init)(PIO pio, uint sm, uint offset, uint txbase, uint baud) {
    pio_sm_claim(pio, sm);

    pio_sm_set_pins_with_mask(pio, sm, 1u << txbase, 1u << txbase);
    pio_sm_set_pindirs_with_mask(pio, sm, 1u << txbase, 1u << txbase);
    pio_gpio_init(pio, txbase);

    pio_sm_config c = suart_tx_program_get_default_config(offset);

    sm_config_set_out_shift(&c, true, false, 16);

    sm_config_set_set_pins(&c, txbase, 1);
    sm_config_set_out_pins(&c, txbase, 1);
    sm_config_set_sideset_pins(&c, txbase);

    sm_config_set_fifo_join(&c, PIO_FIFO_JOIN_TX);

    float div = (float)clock_get_hz(clk_sys) / (8 * baud);
    sm_config_set_clkdiv(&c, div);

    pio_sm_init(pio, sm, offset, &c);
    pio_sm_set_enabled(pio, sm, true);

    return clock_get_hz(clk_sys) / div;
}

static inline void __time_critical_func(suart_tx_program_put)(PIO pio, uint sm, char c) {
    pio_sm_put_blocking(pio, sm, (((uint8_t)c)<<1) | 1);
}

static inline void __time_critical_func(suart_tx_program_puts)(PIO pio, uint sm, const char *s) {
    while (*s)
        suart_tx_program_put(pio, sm, *s++);
}

%}