Skip to content
Switch branches/tags

Name already in use

A tag already exists with the provided branch name. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. Are you sure you want to create this branch?
Go to file
Cannot retrieve contributors at this time
; Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
; SPDX-License-Identifier: BSD-3-Clause
; Transmit a mono or stereo I2S audio stream as stereo
; This is 16 bits per sample; can be altered by modifying the "set" params,
; or made programmable by replacing "set x" with "mov x, y" and using Y as a config register.
; Autopull must be enabled, with threshold set to 32.
; Since I2S is MSB-first, shift direction should be to left.
; Hence the format of the FIFO word is:
; | 31 : 16 | 15 : 0 |
; | sample ws=0 | sample ws=1 |
; Data is output at 1 bit per clock. Use clock divider to adjust frequency.
; Fractional divider will probably be needed to get correct bit clock period,
; but for common syslck freqs this should still give a constant word select period.
; One output pin is used for the data output.
; Two side-set pins are used. Bit 0 is clock, bit 1 is word select.
; Send 16 bit words to the PIO for mono, 32 bit words for stereo
.program audio_i2s
.side_set 2
; /--- LRCLK
; |/-- BCLK
bitloop1: ; ||
out pins, 1 side 0b10
jmp x-- bitloop1 side 0b11
out pins, 1 side 0b00
set x, 14 side 0b01
out pins, 1 side 0b00
jmp x-- bitloop0 side 0b01
out pins, 1 side 0b10
public entry_point:
set x, 14 side 0b11
% c-sdk {
static inline void audio_i2s_program_init(PIO pio, uint sm, uint offset, uint data_pin, uint clock_pin_base) {
pio_sm_config sm_config = audio_i2s_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, 32);
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_jmp(offset + audio_i2s_offset_entry_point));