BlueSCSI-v2/lib/BlueI2S/blue_pio_i2s.pio

; pio_i2s for the Raspberry Pi Pico RP2040
;
; Based loosely off of the MicroPython I2S code in
; https://github.com/micropython/micropython/blob/master/ports/rp2/machine_i2s.c
;
; Copyright (c) 2022 Earle F. Philhower, III <earlephilhower@yahoo.com>
;
; This library is free software; you can redistribute it and/or
; modify it under the terms of the GNU Lesser General Public
; License as published by the Free Software Foundation; either
; version 2.1 of the License, or (at your option) any later version.
;
; This library is distributed in the hope that it will be useful,
; but WITHOUT ANY WARRANTY; without even the implied warranty of
; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
; Lesser General Public License for more details.
;
; You should have received a copy of the GNU Lesser General Public
; License along with this library; if not, write to the Free Software
; Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

.program pio_i2s_out
.side_set 2   ; 0 = bclk, 1=wclk

; The C code should place (number of bits/sample - 2) in Y and
; also update the SHIFTCTRL to be 24 or 32 as appropriate

;                           +----- WCLK
;                           |+---- BCLK
    mov x, y         side 0b01
left:
    out pins, 1      side 0b00
    jmp x--, left    side 0b01
    out pins, 1      side 0b10 ; Last bit of left has WCLK change per I2S spec

    mov x, y         side 0b11
right:
    out pins, 1      side 0b10
    jmp x--, right   side 0b11
    out pins, 1      side 0b00 ; Last bit of right also has WCLK change
    ; Loop back to beginning...

% c-sdk {

static inline void pio_i2s_out_program_init(PIO pio, uint sm, uint offset, uint data_pin, uint clock_pin_base, uint bits) {
    pio_gpio_init(pio, data_pin);
    pio_gpio_init(pio, clock_pin_base);
    pio_gpio_init(pio, clock_pin_base + 1);

    pio_sm_config sm_config =  pio_i2s_out_program_get_default_config(offset);

    sm_config_set_out_pins(&sm_config, data_pin, 1);
    sm_config_set_sideset_pins(&sm_config, clock_pin_base);
    sm_config_set_out_shift(&sm_config, false, true, (bits <= 16) ? 2 * bits : bits);
    sm_config_set_fifo_join(&sm_config, PIO_FIFO_JOIN_TX);

    pio_sm_init(pio, sm, offset, &sm_config);

    uint pin_mask = (1u << data_pin) | (3u << clock_pin_base);
    pio_sm_set_pindirs_with_mask(pio, sm, pin_mask, pin_mask);
    pio_sm_set_pins(pio, sm, 0); // clear pins

    pio_sm_exec(pio, sm, pio_encode_set(pio_y, bits - 2));
}

%}