New dma layout

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
-; 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)
+; 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.
 
 .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:
-    ; 3 lines of broad vertical sync.
-    set x, 2 side 1
+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]
 
-vsync_lines:
-    nop side 0 [14]
+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
+    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.
-    set x, 18 side 1
+    ; 288 active video lines
+    mov x, osr side 0 [1]
 
-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]
+hsync_video:
+    in null, 32 side 1             ; 2us back porch, prepare CPU token
+    push noblock side 1 [1]        ; 4us more back porch, notify CPU early
+    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
 .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