NTSC output

video_dma.pio

@@ -4,78 +4,53 @@
 ; - SM1: sync timing + line start IRQ
 ; - SM0: pixel output during active video
 ;
-; Based on the same timing structure as alanpreed/pico-composite-video:
-; 4us hsync, 6us back porch, 52us active video, 2us front porch,
-; 288 active lines per field, interlaced fields.
+; NTSC-compatible progressive timing using the same coarse 2us timing grid as
+; the original PAL implementation:
+; - 64us line period
+; - 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 = lines_per_field - 1
-; Y   = field flag: 0 = even field, !0 = odd field
+; OSR = active_lines_per_frame - 1
 
 .wrap_target
-vsync_start:
-    ; First set of short pulses:
-    ; 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]
-
-set_even_counter:
-    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
+frame_start:
+    ; 3 lines of broad vertical sync.
     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:
+vsync_lines:
+    nop side 0 [14]
     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 hsync_blank_end side 1 [14]
-    jmp x-- hsync_blank_start side 0 [1]
-hsync_blank_end:
+    jmp x-- vsync_lines side 1
 
-    ; 288 active video lines
-    mov x, osr side 0 [1]
+    ; 19 blank lines before active video.
+    set x, 18 side 1
 
-hsync_video:
-    nop side 1 [2]                 ; 6us back porch
-    irq set LINE_IRQ side 1 [13]   ; 52us active video
-    jmp !x vsync_start side 1 [12] ; 2us front porch (+ tail of active)
-    jmp x-- hsync_video side 0 [1] ; 4us hsync pulse
+blank_lines:
+    irq set DMA_IRQ side 0 [1]
+    nop side 1 [14]
+    jmp x-- blank_lines side 1 [14]
+
+    ; 240 active video lines.
+    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
 
 
@@ -92,8 +67,34 @@ hsync_video:
     set pins, 0
     mov y, x
     wait 1 irq LINE_IRQ
+    irq clear LINE_IRQ
 
 data_out:
     out pins, 1 [DATA_DELAY]
     jmp y-- data_out
-.wrap
+.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