From 9fcb7b3e996ea16e0eb3d43b4280a75aafa95e0d Mon Sep 17 00:00:00 2001
From: giomba <giomba@glgprograms.it>
Date: Sun, 27 Nov 2022 22:07:01 +0100
Subject: [PATCH] Adjustments for front porch calculation.

---
 src/main.c  | 32 +++++++++++++++++++++++++++-----
 src/vga.pio |  7 +++----
 2 files changed, 30 insertions(+), 9 deletions(-)

diff --git a/src/main.c b/src/main.c
index ef453fa..88080c5 100644
--- a/src/main.c
+++ b/src/main.c
@@ -134,6 +134,17 @@ void set_pixel(uint16_t x, uint16_t y)
 	frames[0].data[y * 80 + x / 8] |= (1 << x % 8);
 }
 
+void draw_simple_line(uint16_t x, uint16_t y, uint16_t len, bool horizontal)
+{
+	for (uint16_t i = 0; i < len; ++i)
+	{
+		if (horizontal)
+			set_pixel(x + i, y);
+		else
+			set_pixel(x, y + i);
+	}
+}
+
 /**
  * @brief Represents a program running on the SM of a PIO.
  *
@@ -157,17 +168,28 @@ int main()
 	// horizontal lines
 	for (uint16_t x = 0; x < 639; ++x) // last pixel high -> bad
 	{
-		set_pixel(x, 0);
+		if ((x / 32) % 2 == 0)
+			set_pixel(x, 21);
 		set_pixel(x, 239);
 		set_pixel(x, 479);
 	}
 	// vertical lines
-	for (uint16_t y = 0; y < 480; ++y)
+	for (uint16_t y = 21; y < 480; ++y)
 	{
-		set_pixel(0, y);
+		set_pixel(0 + ((y - 20) / 10) * 4, y);
 		set_pixel(239, y);
 		set_pixel(638, y);
 	}
+	// try to find strangeness using stairs
+	for (uint16_t x = 0; x < 639; ++x)
+	{
+		set_pixel(x, (x / 32) * 4 + 120);
+	}
+	// draw "E" - nice because it's not symmetrical along X
+	draw_simple_line(100, 100, 8, true);
+	draw_simple_line(100, 100, 8, false);
+	draw_simple_line(100, 104, 8, true);
+	draw_simple_line(100, 108, 8, true);
 
 	// Running programs on PIO
 	PIORun vga_hsync, vga_vsync, vga_pixel;
@@ -188,8 +210,8 @@ int main()
 	vga_hsync.sm = pio_claim_unused_sm(vga_hsync.pio, true);
 	vga_hsync_program_init(vga_hsync.pio, vga_hsync.sm, vga_hsync.offset);
 	// low pulse is X pixels long, and SM runs at 4x of pixel clock
-	pio_sm_put_blocking(vga_hsync.pio, vga_hsync.sm, (64 - 1));
-	pio_sm_put_blocking(vga_hsync.pio, vga_hsync.sm, (640 - 1));
+	pio_sm_put_blocking(vga_hsync.pio, vga_hsync.sm, (64 - 2));
+	pio_sm_put_blocking(vga_hsync.pio, vga_hsync.sm, (640 + 16 - 1)); // 16 is front porch
 	printf("OK\n");
 
 	// VGA VSYNC program
diff --git a/src/vga.pio b/src/vga.pio
index 1516745..3f41d26 100644
--- a/src/vga.pio
+++ b/src/vga.pio
@@ -8,7 +8,7 @@ entrypoint_vga_free_run:
     mov x, y
     wait irq 7
 loop:
-    out pins, 1 [3]
+    out pins, 1 [2]
     jmp x-- loop
 .wrap
 
@@ -27,10 +27,9 @@ hsync_pulse:
     jmp x-- hsync_pulse [3]
 
     set pins, 1 [1]
-    set y, 24
+    set y, 27
 hsync_back_porch:
-    jmp y-- hsync_back_porch [19]
-
+    jmp y-- hsync_back_porch [16]
     irq set 7
 
     mov x, osr [3]