apa102.pio

;
; Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
;
; SPDX-License-Identifier: BSD-3-Clause
;
.pio_version 0 // only requires PIO version 0

.program apa102_mini
.side_set 1

; This is really just a TX-only SPI. CLK is side-set pin 0, DIN is OUT pin 0.
; Autopull enabled, threshold 32.
;
; Every word (32 bits) written to the FIFO will be shifted out in its entirety, MSB-first.

    out pins, 1   side 0   ; Stall here when no data (still asserts clock low)
    nop           side 1

% c-sdk {
#include "hardware/clocks.h"
static inline void apa102_mini_program_init(PIO pio, uint sm, uint offset,
        uint baud, uint pin_clk, uint pin_din) {
    pio_sm_set_pins_with_mask(pio, sm, 0, (1u << pin_clk) | (1u << pin_din));
    pio_sm_set_pindirs_with_mask(pio, sm, ~0u, (1u << pin_clk) | (1u << pin_din));
    pio_gpio_init(pio, pin_clk);
    pio_gpio_init(pio, pin_din);

    pio_sm_config c = apa102_mini_program_get_default_config(offset);
    sm_config_set_out_pins(&c, pin_din, 1);
    sm_config_set_sideset_pins(&c, pin_clk);
    // Shift to right, autopull with threshold 32
    sm_config_set_out_shift(&c, false, true, 32);
    // Deeper FIFO as we're not doing any RX
    sm_config_set_fifo_join(&c, PIO_FIFO_JOIN_TX);
    // We transmit 1 bit every 2 execution cycles
    float div = (float)clock_get_hz(clk_sys) / (2 * baud);
    sm_config_set_clkdiv(&c, div);

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

.program apa102_rgb555

; Alternative program to unpack two RGB555 pixels from a FIFO word and transmit.
; This makes it easier to DMA large buffers without processor involvement.

; OSR: shift to right
; ISR: shift to right

; To set brightness, set ISR to bit-reverse of 5-bit brightness,
; followed by 111. (00...00_b0b1b2b3b4_111)

; DMA pixel format is 0RRRRRGGGGGBBBBB x2 (15 bpp, 2px per FIFO word)

; APA102 command structure:
; increasing time ---->>
;             | byte 3 | byte 2 | byte 1 | byte 0 |
;             |7      0|7      0|7      0|7      0|
;             -------------------------------------
; Pixel       |111bbbbb|BBBBBBBB|GGGGGGGG|RRRRRRRR|
; Start Frame |00000000|00000000|00000000|00000000|
; Stop Frame  |11111111|11111111|11111111|11111111|

.wrap_target
public pixel_out:
    ; pixel_out formats an APA102 colour command in the ISR.
    ; bit_run shifts 32 bits out of the ISR, with clock.
    pull ifempty
    set x, 2
colour_loop:
    in osr, 5
    out null, 5
    in null, 3
    jmp x-- colour_loop
    in y, 8
    mov isr, ::isr ; reverse for msb-first wire order
    out null, 1
public bit_run:
    ; in isr, n rotates ISR by n bits (right rotation only)
    ; Use this to perform out shifts from ISR, via mov pins
    set x, 31
bit_out:
    set pins, 0
    mov pins, isr [6]
    set pins, 1
    in isr, 1 [6]
    jmp x-- bit_out
.wrap