duart_tx.pio

.program duart_tx
; An 8n1 UART transmit program.
; SET & OUT pins should be set to TX+/TX-
    set PINS, 0b10
    set PINDIRS, 0b11
.wrap_target
    out PINS,    2     [7] ; Shift 2 bits from OSR to the OUT pins, delay 7 cycles
.wrap

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

uint32_t txtab[256];

static inline int __time_critical_func(duart_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, 3u << txbase, 3u << txbase);
    pio_sm_set_pindirs_with_mask(pio, sm, 3u << txbase, 3u << txbase);
    pio_gpio_init(pio, txbase);
    pio_gpio_init(pio, txbase+1);

    pio_sm_config c = duart_tx_program_get_default_config(offset);

    sm_config_set_out_shift(&c, true, true, 24);

    sm_config_set_set_pins(&c, txbase, 2);
    sm_config_set_out_pins(&c, txbase, 2);

    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);

    for(uint i = 0; i < 256; i++) {
        txtab[i] = 0x55540002 |
            ((i & 0x01) ? (0b01 <<  2) : (0b10 <<  2)) |
            ((i & 0x02) ? (0b01 <<  4) : (0b10 <<  4)) |
            ((i & 0x04) ? (0b01 <<  6) : (0b10 <<  6)) |
            ((i & 0x08) ? (0b01 <<  8) : (0b10 <<  8)) |
            ((i & 0x10) ? (0b01 << 10) : (0b10 << 10)) |
            ((i & 0x20) ? (0b01 << 12) : (0b10 << 12)) |
            ((i & 0x40) ? (0b01 << 14) : (0b10 << 14)) |
            ((i & 0x80) ? (0b01 << 16) : (0b10 << 16));
    }

    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(duart_tx_program_put)(PIO pio, uint sm, char c) {
    pio_sm_put_blocking(pio, sm, txtab[(uint8_t)c]);
}

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

%}