New dma layout

main.c

@@ -20,20 +20,16 @@
 #define DATA_PIN         2   // pixel / luma bit pin
 #define SYNC_PIN         3   // sync pin
 
-// Set to 1 to bypass DMA/framebuffer and generate fixed black/white bars.
-#define VIDEO_DIAGNOSTIC_BARS 0
-
 // ---------------------------
 // Video format
 // ---------------------------
-// NTSC-compatible 240p timing using the same 64us line structure as the
-// original PAL code, but with 262 lines/frame at about 59.6Hz.
 #define VIDEO_WIDTH      768
-#define VIDEO_HEIGHT     240
+#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   0.000050f   // 52 us active video per line
+#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.
@@ -47,8 +43,11 @@
 // ---------------------------
 static uint32_t framebuffer[VIDEO_HEIGHT][WORDS_PER_LINE];
 
-// Current active scanline within the progressive frame.
+// Field/line tracking for line-based DMA.
-static volatile uint line_in_frame = 0;
+// 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;
@@ -57,6 +56,7 @@ static int video_dma_chan;
 // Optional test pattern
 // Replace this with your own drawing code.
 // ---------------------------
+#define BORDER 40
 static void fill_test_pattern(void) {
     memset(framebuffer, 0x00, sizeof(framebuffer));
 
@@ -66,7 +66,7 @@ static void fill_test_pattern(void) {
 
             // Simple visible pattern:
             // border + checker
-            if (x < 20 || x >= VIDEO_WIDTH - 20 || y < 20 || y >= VIDEO_HEIGHT - 20) {
+            if (x < BORDER || x >= VIDEO_WIDTH - BORDER || y < BORDER || y >= VIDEO_HEIGHT - BORDER) {
                 on = true;
             } else if (((x >> 4) ^ (y >> 4)) & 1) {
                 on = true;
@@ -107,18 +107,6 @@ static void init_cvdata_program(PIO pio, uint sm, uint offset, float clkdiv, uin
     pio_sm_exec(pio, sm, pio_encode_out(pio_null, 32));
 }
 
-static void init_cvdata_diag_program(PIO pio, uint sm, uint offset, float clkdiv, uint data_pin) {
-    pio_sm_config c = cvdata_diag_program_get_default_config(offset);
-
-    sm_config_set_set_pins(&c, data_pin, 1);
-    sm_config_set_clkdiv(&c, clkdiv);
-
-    pio_gpio_init(pio, data_pin);
-    pio_sm_set_consecutive_pindirs(pio, sm, data_pin, 1, true);
-
-    pio_sm_init(pio, sm, offset, &c);
-}
-
 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);
 
@@ -130,9 +118,12 @@ static void init_cvsync_program(PIO pio, uint sm, uint offset, float clkdiv, uin
 
     pio_sm_init(pio, sm, offset, &c);
 
-    // Preload OSR = active_lines_per_frame - 1
+    // Preload OSR = lines_per_field - 1
-    pio_sm_put_blocking(pio, sm, VIDEO_HEIGHT - 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));
 }
 
 // ---------------------------
@@ -163,31 +154,30 @@ static void init_video_dma(PIO pio, uint data_sm) {
 // Start DMA for one scanline
 // ---------------------------
 static inline void start_dma_for_current_line(void) {
-    dma_channel_set_read_addr(video_dma_chan, framebuffer[line_in_frame], false);
+    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_frame++;
+    line_in_field++;
-    if (line_in_frame >= VIDEO_HEIGHT) {
+    if (line_in_field >= LINES_PER_FIELD) {
-        line_in_frame = 0;
+        line_in_field = 0;
+        even_field = !even_field;
     }
 }
 
 // ---------------------------
 // PIO IRQ handler:
-// fires once per active scanline when cvsync executes `irq set LINE_IRQ`.
+// The sync SM pushes one token into its RX FIFO during each line's back porch.
-// We clear the PIO IRQ and arm one DMA transfer for the next active line.
+// As soon as the previous line DMA has finished, consume one token and arm the
+// next scanline so the data FIFO is primed before visible pixels start.
 // ---------------------------
 static void pio0_irq0_handler(void) {
-    if (pio_interrupt_get(VIDEO_PIO, 1)) {
+    if (!pio_sm_is_rx_fifo_empty(VIDEO_PIO, SYNC_SM) && !dma_channel_is_busy(video_dma_chan)) {
-        pio_interrupt_clear(VIDEO_PIO, 1);
+        (void)pio_sm_get(VIDEO_PIO, SYNC_SM);
-
-        // A new line request arrives during hsync/back porch so the DMA can
-        // prime the data SM before visible pixels begin.
-        if (!dma_channel_is_busy(video_dma_chan)) {
         start_dma_for_current_line();
     }
 }
-}
 
 // ---------------------------
 // Video start
@@ -198,41 +188,30 @@ static void video_init(void) {
     }
 
     uint sync_offset = pio_add_program(VIDEO_PIO, &cvsync_program);
-    uint data_offset;
+    uint data_offset = pio_add_program(VIDEO_PIO, &cvdata_program);
 
-    // sync SM: 1 instruction every 0.5 us
+    // 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_cvsync_program(VIDEO_PIO, SYNC_SM, sync_offset, sync_clkdiv, SYNC_PIN);
-
-#if VIDEO_DIAGNOSTIC_BARS
-    // 0.5 us per instruction gives a visible bar pattern over the 52 us active period.
-    float diag_clkdiv = sys_hz * 0.0000005f;
-    data_offset = pio_add_program(VIDEO_PIO, &cvdata_diag_program);
-    init_cvdata_diag_program(VIDEO_PIO, DATA_SM, data_offset, diag_clkdiv, DATA_PIN);
-#else
-    // data SM: enough PIO cycles to emit VIDEO_WIDTH bits in 52 us
-    float data_clkdiv = (sys_hz / ((float)VIDEO_WIDTH / ACTIVE_VIDEO_S)) / (float)CLOCKS_PER_BIT;
-    data_offset = pio_add_program(VIDEO_PIO, &cvdata_program);
     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);
-#endif
 
-    // Route PIO internal IRQ 1 to CPU IRQ 0. IRQ 0 stays reserved for the
+    // Route sync-SM RX FIFO notifications to CPU IRQ 0.
-    // data SM's wait instruction inside the PIO block.
+    pio_set_irq0_source_enabled(VIDEO_PIO, pis_sm1_rx_fifo_not_empty, true);
-    pio_interrupt_clear(VIDEO_PIO, 0);
-    pio_interrupt_clear(VIDEO_PIO, 1);
-    pio_set_irq0_source_enabled(VIDEO_PIO, pis_interrupt1, true);
     irq_set_exclusive_handler(PIO0_IRQ_0, pio0_irq0_handler);
     irq_set_enabled(PIO0_IRQ_0, true);
 
-    // Start with the first active line of the frame.
+    // Start with the first line of the even field
-    line_in_frame = 0;
+    even_field = true;
+    line_in_field = 0;
 
-#if !VIDEO_DIAGNOSTIC_BARS
+    // Prime the FIFO so the very first active line does not depend on IRQ latency.
     start_dma_for_current_line();
-#endif
 
     pio_sm_set_enabled(VIDEO_PIO, DATA_SM, true);
     pio_sm_set_enabled(VIDEO_PIO, SYNC_SM, true);

video_dma.pio

@@ -4,53 +4,79 @@
 ; - SM1: sync timing + line start IRQ
 ; - SM0: pixel output during active video
 ;
-; NTSC-compatible progressive timing using the same coarse 2us timing grid as
+; Based on the same timing structure as alanpreed/pico-composite-video:
-; the original PAL implementation:
+; 4us hsync, 6us back porch, 52us active video, 2us front porch,
-; - 64us line period
+; 288 active lines per field, interlaced fields.
-; - 4us hsync
-; - 6us back porch
-; - 52us active video + front porch tail
-; - 240 active lines, 262 total lines per frame (~59.64Hz)
 
 .define DATA_DELAY 4
 .define LINE_IRQ 0
-.define DMA_IRQ 1
 .define PUBLIC CLOCKS_PER_BIT DATA_DELAY + 2
 
 .program cvsync
 .side_set 1
 
-; OSR = active_lines_per_frame - 1
+; OSR = lines_per_field - 1
+; Y   = field flag: 0 = even field, !0 = odd field
 
 .wrap_target
-frame_start:
+vsync_start:
-    ; 3 lines of broad vertical sync.
+    ; First set of short pulses:
-    set x, 2 side 1
+    ; even field: 6
+    ; odd field : 5
+    jmp !y set_even_counter side 0
+    set x, 3 side 1
+    jmp vsync_short_pulse side 1 [13]
 
-vsync_lines:
+set_even_counter:
-    nop side 0 [14]
+    set x, 4 side 1 [14]
+
+vsync_short_pulse:
     nop side 0
+    jmp x-- vsync_short_pulse [14] side 1
+
+    ; Long sync pulses: always 5
+    set x, 4 side 0 [13]
+
+vsync_long_start:
+    jmp !x vsync_long_end [1] side 1
+    jmp x-- vsync_long_start [13] side 0
+vsync_long_end:
+
+    ; Second set of short pulses:
+    ; even field: 5
+    ; odd field : 4
+    jmp !y set_even_counter_2 side 0
+    set x, 2 side 1
+    jmp flip_field_flag side 1 [12]
+
+set_even_counter_2:
+    set x, 3 side 1 [13]
+
+flip_field_flag:
+    mov y, !y side 1
+
+vsync_short_pulse_2:
+    nop side 0
+    jmp x-- vsync_short_pulse_2 [14] side 1
+
+    ; 17 blank lines
+    set x, 16 side 0 [1]
+
+hsync_blank_start:
     nop side 1 [14]
-    jmp x-- vsync_lines side 1
+    jmp !x hsync_blank_end side 1 [14]
+    jmp x-- hsync_blank_start side 0 [1]
+hsync_blank_end:
 
-    ; 19 blank lines before active video.
+    ; 288 active video lines
-    set x, 18 side 1
+    mov x, osr side 0 [1]
 
-blank_lines:
+hsync_video:
-    irq set DMA_IRQ side 0 [1]
+    in null, 32 side 1             ; 2us back porch, prepare CPU token
-    nop side 1 [14]
+    push noblock side 1 [1]        ; 4us more back porch, notify CPU early
-    jmp x-- blank_lines side 1 [14]
+    irq set LINE_IRQ side 1 [13]   ; 52us active video
-
+    jmp !x vsync_start side 1 [12] ; 2us front porch (+ tail of active)
-    ; 240 active video lines.
+    jmp x-- hsync_video side 0 [1] ; 4us hsync pulse
-    mov x, osr side 1
-
-active_lines:
-    irq set DMA_IRQ side 0 [1]    ; 4us hsync, ask CPU to arm DMA
-    nop side 1 [2]                ; 6us back porch
-    irq set LINE_IRQ side 1 [13]  ; 28us visible video
-    jmp x-- active_lines side 1 [12]
-
-    jmp frame_start side 1 [12]
 .wrap
 
 
@@ -73,28 +99,3 @@ data_out:
     out pins, 1 [DATA_DELAY]
     jmp y-- data_out
 .wrap
-
-
-.program cvdata_diag
-
-; Diagnostic program:
-; waits for each active line, then emits wide black/white bars without DMA.
-; This isolates the analog output path from the framebuffer/DMA path.
-
-.wrap_target
-    wait 1 irq LINE_IRQ
-    irq clear LINE_IRQ
-
-    set x, 3
-
-diag_bars:
-    set pins, 1 [15]
-    nop      [15]
-    nop      [15]
-    set pins, 0 [15]
-    nop      [15]
-    nop      [15]
-    jmp x-- diag_bars [15]
-
-    set pins, 0
-.wrap