kopia lustrzana https://github.com/pimoroni/pimoroni-pico
63 wiersze
2.1 KiB
Plaintext
63 wiersze
2.1 KiB
Plaintext
;
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; Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
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;
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; SPDX-License-Identifier: BSD-3-Clause
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;
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; Transmit a mono or stereo I2S audio stream as stereo
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; This is 16 bits per sample; can be altered by modifying the "set" params,
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; or made programmable by replacing "set x" with "mov x, y" and using Y as a config register.
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;
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; Autopull must be enabled, with threshold set to 32.
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; Since I2S is MSB-first, shift direction should be to left.
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; Hence the format of the FIFO word is:
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;
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; | 31 : 16 | 15 : 0 |
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; | sample ws=0 | sample ws=1 |
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;
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; Data is output at 1 bit per clock. Use clock divider to adjust frequency.
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; Fractional divider will probably be needed to get correct bit clock period,
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; but for common syslck freqs this should still give a constant word select period.
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;
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; One output pin is used for the data output.
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; Two side-set pins are used. Bit 0 is clock, bit 1 is word select.
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; Send 16 bit words to the PIO for mono, 32 bit words for stereo
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.program audio_i2s
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.side_set 2
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; /--- LRCLK
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; |/-- BCLK
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bitloop1: ; ||
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out pins, 1 side 0b10
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jmp x-- bitloop1 side 0b11
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out pins, 1 side 0b00
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set x, 14 side 0b01
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bitloop0:
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out pins, 1 side 0b00
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jmp x-- bitloop0 side 0b01
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out pins, 1 side 0b10
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public entry_point:
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set x, 14 side 0b11
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% c-sdk {
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static inline void audio_i2s_program_init(PIO pio, uint sm, uint offset, uint data_pin, uint clock_pin_base) {
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pio_sm_config sm_config = audio_i2s_program_get_default_config(offset);
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sm_config_set_out_pins(&sm_config, data_pin, 1);
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sm_config_set_sideset_pins(&sm_config, clock_pin_base);
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sm_config_set_out_shift(&sm_config, false, true, 32);
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pio_sm_init(pio, sm, offset, &sm_config);
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uint pin_mask = (1u << data_pin) | (3u << clock_pin_base);
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pio_sm_set_pindirs_with_mask(pio, sm, pin_mask, pin_mask);
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pio_sm_set_pins_with_mask(pio, sm, 0, pin_mask); // clear pins
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pio_sm_exec(pio, sm, pio_encode_jmp(offset + audio_i2s_offset_entry_point));
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}
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%} |