From 55559b6b89ce7025b1e1f72792eeef947e76137b Mon Sep 17 00:00:00 2001
From: giomba <giomba@glgprograms.it>
Date: Tue, 11 Oct 2022 20:39:22 +0200
Subject: [PATCH] Horizontal sync experiment.

---
 src/main.c  | 25 +++++++++++++++++++------
 src/vga.pio | 17 +++++++++++------
 2 files changed, 30 insertions(+), 12 deletions(-)

diff --git a/src/main.c b/src/main.c
index 4cff308..00cfb99 100644
--- a/src/main.c
+++ b/src/main.c
@@ -36,6 +36,7 @@ static void vga_pixel_program_init(PIO pio, uint sm, uint offset)
 {
 	// magic definition of the called function?
 	pio_sm_config c = vga_free_run_program_get_default_config(offset);
+	// destination pins for OUT instructions
 	sm_config_set_out_pins(&c, 22, 1);
 	pio_gpio_init(pio, 22);
 	pio_sm_set_consecutive_pindirs(pio, sm, 22, 1, true);
@@ -55,7 +56,8 @@ static void vga_pixel_program_init(PIO pio, uint sm, uint offset)
 static void vga_sync_program_init(PIO pio, uint sm, uint offset)
 {
 	pio_sm_config config = vga_sync_program_get_default_config(offset);
-	sm_config_set_out_pins(&config, 20, 2);
+	// destination pins for SET instructions
+	sm_config_set_set_pins(&config, 20, 2);
 	pio_gpio_init(pio, 20);
 	pio_sm_set_consecutive_pindirs(pio, sm, 20, 2, true);
 
@@ -63,6 +65,8 @@ static void vga_sync_program_init(PIO pio, uint sm, uint offset)
 
 	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);
 }
 
@@ -102,14 +106,23 @@ int main()
 
 	printf("Welcome.\n");
 
-	// feed pixel program
 	while (true)
 	{
-		for (size_t i = 0; i < sizeof(frames[0].data); ++i)
+		for (size_t i = 0; i < sizeof(frames[0].data);)
 		{
-			pio_sm_put_blocking(pio, sm0, frames[0].data[i]);
+			// feed sync machine
+			if (pio_sm_get_tx_fifo_level(pio, sm1) <= 4)
+			{
+				pio_sm_put_blocking(pio, sm1, 63 * 4);
+				pio_sm_put_blocking(pio, sm1, 775 * 4);
+			}
+
+			// feed pixel machine
+			if (!pio_sm_is_tx_fifo_full(pio, sm0))
+				pio_sm_put_blocking(pio, sm0, frames[0].data[i++]);
 		}
-		printf(".");
-		sleep_ms(1000);
+		// printf(".");
+
+		// sleep_ms(1000);
 	}
 }
diff --git a/src/vga.pio b/src/vga.pio
index 823f81b..0d985dd 100644
--- a/src/vga.pio
+++ b/src/vga.pio
@@ -10,10 +10,15 @@ loop:
 
 entrypoint_vga_sync:
 loop:
-    set x, 31
-    mov osr, x
-    out pins, 1 [30]
-    set x, 0
-    mov osr, x
-    out pins, 1 [30]
+    pull
+    mov x, osr
+    set pins, 0
+hsync_pulse:
+    jmp x-- hsync_pulse
+
+    pull
+    mov x, osr
+    set pins, 1
+hsync_idle:
+    jmp x-- hsync_idle
     jmp loop