From a5339f6fcfe1fd474345e15669f9b54b8b58138b Mon Sep 17 00:00:00 2001
From: giomba <giomba@glgprograms.it>
Date: Wed, 12 Oct 2022 20:44:26 +0200
Subject: [PATCH] Add vertical sync to VGA (out of phase).

---
 src/main.c  | 32 +++++++++++++++++++++++++++++---
 src/vga.pio | 19 +++++++++++++++++++
 2 files changed, 48 insertions(+), 3 deletions(-)

diff --git a/src/main.c b/src/main.c
index 49dc1a2..47c84a8 100644
--- a/src/main.c
+++ b/src/main.c
@@ -57,9 +57,26 @@ static void vga_hsync_program_init(PIO pio, uint sm, uint offset)
 {
 	pio_sm_config config = vga_hsync_program_get_default_config(offset);
 	// destination pins for SET instructions
-	sm_config_set_set_pins(&config, 20, 2);
+	sm_config_set_set_pins(&config, 20, 1);
 	pio_gpio_init(pio, 20);
-	pio_sm_set_consecutive_pindirs(pio, sm, 20, 2, true);
+	pio_sm_set_consecutive_pindirs(pio, sm, 20, 1, true);
+
+	pio_sm_init(pio, sm, offset, &config);
+
+	pio_sm_set_clkdiv_int_frac(pio, sm, 1, 0);
+
+	pio->sm->shiftctrl = (1 << PIO_SM0_SHIFTCTRL_FJOIN_TX_LSB);
+
+	pio_sm_set_enabled(pio, sm, true);
+}
+
+static void vga_vsync_program_init(PIO pio, uint sm, uint offset)
+{
+	pio_sm_config config = vga_vsync_program_get_default_config(offset);
+	// destination pins for SET instructions
+	sm_config_set_set_pins(&config, 21, 1);
+	pio_gpio_init(pio, 21);
+	pio_sm_set_consecutive_pindirs(pio, sm, 21, 1, true);
 
 	pio_sm_init(pio, sm, offset, &config);
 
@@ -98,7 +115,7 @@ int main()
 	printf("Starting VGA pixel machine on %u...\n", sm0);
 	vga_pixel_program_init(pio, sm0, offset0);
 
-	// VGA sync program
+	// VGA HSYNC program
 	uint offset1 = pio_add_program(pio, &vga_hsync_program);
 	uint sm1 = pio_claim_unused_sm(pio, true);
 	printf("Starting VGA sync machine on %u...\n", sm1);
@@ -108,6 +125,15 @@ int main()
 	pio_sm_put_blocking(pio, sm1, 63 * 4);
 	pio_sm_put_blocking(pio, sm1, 775 * 4);
 
+	// VGA VSYNC program
+	uint offset2 = pio_add_program(pio, &vga_vsync_program);
+	uint sm2 = pio_claim_unused_sm(pio, true);
+	printf("Starting VGA vsync machine on %u...\n", sm2);
+	vga_vsync_program_init(pio, sm2, offset2);
+	printf("Feeding vertical sync...\n");
+	pio_sm_put_blocking(pio, sm2, 2520 * 4);
+	pio_sm_put_blocking(pio, sm2, 420000 * 4);
+
 	printf("Start!\n");
 
 	while (true)
diff --git a/src/vga.pio b/src/vga.pio
index 2a1c368..007533f 100644
--- a/src/vga.pio
+++ b/src/vga.pio
@@ -24,3 +24,22 @@ hsync_pulse:
 hsync_idle:
     jmp x-- hsync_idle
     jmp loop
+
+.program vga_vsync
+
+entrypoint_vga_vsync:
+    pull
+    mov isr, osr
+    pull
+
+loop:
+    mov x, isr
+    set pins, 0
+vsync_pulse:
+    jmp x-- vsync_pulse
+
+    mov x, osr
+    set pins, 1
+vsync_idle:
+    jmp x-- vsync_idle
+    jmp loop