picopal/main.c

// main.c
#include <stdio.h>
#include <string.h>

#include "pico/stdlib.h"
#include "hardware/clocks.h"
#include "hardware/dma.h"
#include "hardware/irq.h"
#include "hardware/pio.h"

#include "video_dma.pio.h"

// ---------------------------
// User-adjustable pins
// ---------------------------
#define VIDEO_PIO        pio0
#define DATA_SM          0
#define SYNC_SM          1

#define DATA_PIN         2   // pixel / luma bit pin
#define SYNC_PIN         3   // sync pin

// ---------------------------
// Video format
// ---------------------------
#define VIDEO_WIDTH      768
#define VIDEO_HEIGHT     576
#define WORDS_PER_LINE   (VIDEO_WIDTH / 32)
#define LINES_PER_FIELD  (VIDEO_HEIGHT / 2)

#define SYNC_INTERVAL_S  0.000002f   // 2 us per sync-SM instruction
#define ACTIVE_VIDEO_S   0.000052f   // 52 us active video per line

// Match the .pio program's published constant.
// pioasm will emit CLOCKS_PER_BIT in the generated header.
#ifndef CLOCKS_PER_BIT
#define CLOCKS_PER_BIT 6
#endif

// ---------------------------
// Framebuffer
// One bit per pixel, 32 pixels per word
// ---------------------------
static uint32_t framebuffer[VIDEO_HEIGHT][WORDS_PER_LINE];

// Field/line tracking for line-based DMA.
// This is intentionally kept in software to match the sync SM's 288 active
// lines per field.
static volatile bool even_field = true;
static volatile uint line_in_field = 0;

// DMA channel that feeds the PIO TX FIFO
static int video_dma_chan;

// ---------------------------
// Optional test pattern
// Replace this with your own drawing code.
// ---------------------------
static void fill_test_pattern(void) {
    memset(framebuffer, 0x00, sizeof(framebuffer));

    for (uint y = 0; y < VIDEO_HEIGHT; ++y) {
        for (uint x = 0; x < VIDEO_WIDTH; ++x) {
            bool on = false;

            // Simple visible pattern:
            // border + checker
            if (x < 8 || x >= VIDEO_WIDTH - 8 || y < 8 || y >= VIDEO_HEIGHT - 8) {
                on = true;
            } else if (((x >> 4) ^ (y >> 4)) & 1) {
                on = true;
            }

            if (on) {
                uint word = x >> 5;
                uint bit  = 31 - (x & 31);   // MSB-first
                framebuffer[y][word] |= (1u << bit);
            }
        }
    }
}

// ---------------------------
// PIO init helpers
// ---------------------------
static void init_cvdata_program(PIO pio, uint sm, uint offset, float clkdiv, uint data_pin) {
    pio_sm_config c = cvdata_program_get_default_config(offset);

    sm_config_set_set_pins(&c, data_pin, 1);
    sm_config_set_out_pins(&c, data_pin, 1);
    sm_config_set_clkdiv(&c, clkdiv);

    // Shift left, autopull every 32 bits.
    // If the image is mirrored, change this to shift-right and/or change bit packing.
    sm_config_set_out_shift(&c, false, true, 32);

    pio_gpio_init(pio, data_pin);
    pio_sm_set_consecutive_pindirs(pio, sm, data_pin, 1, true);

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

    // Preload X = VIDEO_WIDTH - 1
    pio_sm_put_blocking(pio, sm, VIDEO_WIDTH - 1);
    pio_sm_exec(pio, sm, pio_encode_pull(false, false));
    pio_sm_exec(pio, sm, pio_encode_mov(pio_x, pio_osr));
    pio_sm_exec(pio, sm, pio_encode_out(pio_null, 32));
}

static void init_cvsync_program(PIO pio, uint sm, uint offset, float clkdiv, uint sync_pin) {
    pio_sm_config c = cvsync_program_get_default_config(offset);

    sm_config_set_sideset_pins(&c, sync_pin);
    sm_config_set_clkdiv(&c, clkdiv);

    pio_gpio_init(pio, sync_pin);
    pio_sm_set_consecutive_pindirs(pio, sm, sync_pin, 1, true);

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

    // Preload OSR = lines_per_field - 1
    pio_sm_put_blocking(pio, sm, LINES_PER_FIELD - 1);
    pio_sm_exec(pio, sm, pio_encode_pull(false, false));

    // Start with Y = 0, meaning "even field" in this program.
    pio_sm_exec(pio, sm, pio_encode_set(pio_y, 0));
}

// ---------------------------
// DMA setup
// ---------------------------
static void init_video_dma(PIO pio, uint data_sm) {
    video_dma_chan = dma_claim_unused_channel(true);

    dma_channel_config cfg = dma_channel_get_default_config(video_dma_chan);
    channel_config_set_transfer_data_size(&cfg, DMA_SIZE_32);
    channel_config_set_read_increment(&cfg, true);
    channel_config_set_write_increment(&cfg, false);

    // Pace the DMA from the data SM TX FIFO DREQ
    channel_config_set_dreq(&cfg, pio_get_dreq(pio, data_sm, true));

    dma_channel_configure(
        video_dma_chan,
        &cfg,
        &pio->txf[data_sm], // write address
        NULL,               // read address set per line
        0,                  // transfer count set per line
        false               // don't start yet
    );
}

// ---------------------------
// Start DMA for one scanline
// ---------------------------
static inline void start_dma_for_current_line(void) {
    uint src_line = even_field ? (line_in_field * 2u) : (line_in_field * 2u + 1u);

    dma_channel_set_read_addr(video_dma_chan, framebuffer[src_line], false);
    dma_channel_set_trans_count(video_dma_chan, WORDS_PER_LINE, true);

    line_in_field++;
    if (line_in_field >= LINES_PER_FIELD) {
        line_in_field = 0;
        even_field = !even_field;
    }
}

// ---------------------------
// PIO IRQ handler:
// fires once per active scanline when cvsync executes `irq set LINE_IRQ`.
// We clear the PIO IRQ and arm one DMA transfer for the next active line.
// ---------------------------
static void pio0_irq0_handler(void) {
    if (pio_interrupt_get(VIDEO_PIO, 0)) {
        pio_interrupt_clear(VIDEO_PIO, 0);

        // Safety: a new line should only arrive after the previous line DMA is done.
        // If it isn't, the clocks are wrong or something stalled badly.
        if (!dma_channel_is_busy(video_dma_chan)) {
            start_dma_for_current_line();
        }
    }
}

// ---------------------------
// Video start
// ---------------------------
static void video_init(void) {
    if ((VIDEO_WIDTH % 32) != 0) {
        panic("VIDEO_WIDTH must be a multiple of 32");
    }

    uint sync_offset = pio_add_program(VIDEO_PIO, &cvsync_program);
    uint data_offset = pio_add_program(VIDEO_PIO, &cvdata_program);

    // Same timing idea as the original repo:
    // sync SM: 1 instruction every 2 us
    // data SM: enough PIO cycles to emit VIDEO_WIDTH bits in 52 us
    float sys_hz = (float)clock_get_hz(clk_sys);
    float data_clkdiv = (sys_hz / ((float)VIDEO_WIDTH / ACTIVE_VIDEO_S)) / (float)CLOCKS_PER_BIT;
    float sync_clkdiv = sys_hz * SYNC_INTERVAL_S;

    init_cvdata_program(VIDEO_PIO, DATA_SM, data_offset, data_clkdiv, DATA_PIN);
    init_cvsync_program(VIDEO_PIO, SYNC_SM, sync_offset, sync_clkdiv, SYNC_PIN);
    init_video_dma(VIDEO_PIO, DATA_SM);

    // Route PIO internal IRQ 0 to CPU IRQ 0
    pio_set_irq0_source_enabled(VIDEO_PIO, pis_interrupt0, true);
    irq_set_exclusive_handler(PIO0_IRQ_0, pio0_irq0_handler);
    irq_set_enabled(PIO0_IRQ_0, true);

    // Start with the first line of the even field
    even_field = true;
    line_in_field = 0;

    pio_sm_set_enabled(VIDEO_PIO, DATA_SM, true);
    pio_sm_set_enabled(VIDEO_PIO, SYNC_SM, true);
}

int main(void) {
    stdio_init_all();

    fill_test_pattern();   // Replace with your own framebuffer writer
    video_init();

    while (true) {
        // Your application code goes here.
        // Some other code can freely draw into framebuffer[].
        tight_loop_contents();
    }
}