Basic pattern gen

video_dma.pio

@@ -0,0 +1,99 @@
+; video_dma.pio
+;
+; Composite video generator:
+; - 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.
+
+.define DATA_DELAY 4
+.define LINE_IRQ 0
+.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
+
+.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
+    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 hsync_blank_end side 1 [14]
+    jmp x-- hsync_blank_start side 0 [1]
+hsync_blank_end:
+
+    ; 288 active video lines
+    mov x, osr side 0 [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
+.wrap
+
+
+.program cvdata
+
+; X = pixels_per_line - 1, preloaded once from C
+; Each line:
+;   clear output
+;   reload Y from X
+;   wait for sync SM to raise LINE_IRQ
+;   shift out one bit per loop
+
+.wrap_target
+    set pins, 0
+    mov y, x
+    wait 1 irq LINE_IRQ
+
+data_out:
+    out pins, 1 [DATA_DELAY]
+    jmp y-- data_out
+.wrap