From bbe42f31bbc76dbb404c0fceb0efbdfc20be7f51 Mon Sep 17 00:00:00 2001
From: giomba <giomba@glgprograms.it>
Date: Mon, 10 Oct 2022 19:10:52 +0200
Subject: [PATCH] Add freerunning VGA pixel clock draft.

---
 CMakeLists.txt | 10 +++++-
 src/main.c     | 87 ++++++++++++++++++++++++++++++++++++++++++++------
 src/vga.pio    |  9 ++++++
 3 files changed, 95 insertions(+), 11 deletions(-)
 create mode 100644 src/vga.pio

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 2a269a7..f22f1bb 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -26,6 +26,11 @@ add_executable(ceda2vga
         src/main.c
         )
 
+pico_generate_pio_header(ceda2vga
+        ${CMAKE_CURRENT_LIST_DIR}/src/vga.pio
+        )
+
+# configure stdio to make I/O on virtual usb serial port
 pico_enable_stdio_usb(ceda2vga 1)
 pico_enable_stdio_uart(ceda2vga 0)
 
@@ -33,7 +38,10 @@ pico_enable_stdio_uart(ceda2vga 0)
 pico_add_extra_outputs(ceda2vga)
 
 # pull in common dependencies
-target_link_libraries(ceda2vga pico_stdlib)
+target_link_libraries(ceda2vga
+        pico_stdlib
+        hardware_pio
+        )
 
 # add url via pico_set_program_url
 # example_auto_set_url(ceda2vga)
diff --git a/src/main.c b/src/main.c
index 6062022..e098766 100644
--- a/src/main.c
+++ b/src/main.c
@@ -7,22 +7,89 @@
  *
  */
 
+#include "hardware/clocks.h"
+#include "hardware/pio.h"
+#include "hardware/pll.h"
+#include "hardware/structs/pio.h"
 #include "pico/stdlib.h"
 
+#include <stdint.h>
+
+#include "vga.pio.h"
+
 #include <stdio.h>
 
-int main() {
-  stdio_init_all();
-  unsigned int count = 0;
+#define FRAMES 2
 
+#define HPIXEL 640
+#define VPIXEL 480
+#define BPP    1
+
+typedef struct Frame
+{
+	uint8_t data[HPIXEL * VPIXEL * BPP / 8];
+} Frame;
+
+static Frame frames[FRAMES] = {0};
+
+static void vga_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);
+	sm_config_set_out_pins(&c, 22, 1);
+
+	pio_gpio_init(pio, 22);
+	pio_sm_set_consecutive_pindirs(pio, sm, 22, 1, true);
+
+	pio_sm_init(pio, sm, offset, &c);
+
+	pio_sm_set_clkdiv_int_frac(pio, sm, 1, 0);
+
+	pio->sm->shiftctrl = (1 << PIO_SM0_SHIFTCTRL_FJOIN_TX_LSB) |
+	                     (1 << PIO_SM0_SHIFTCTRL_OUT_SHIFTDIR_LSB) |
+	                     (1 << PIO_SM0_SHIFTCTRL_OUT_SHIFTDIR_LSB) |
+	                     (1 << PIO_SM0_SHIFTCTRL_AUTOPULL_LSB);
+
+	pio_sm_set_enabled(pio, sm, true);
+}
+
+int main()
+{
+	// main clock = VCO / divider1 / divider2 = 126MHz
+	pll_init(pll_sys, 1, 1500 * MHZ, 6, 2);
+
+	stdio_init_all();
+
+#if 0
   const uint LED_PIN = PICO_DEFAULT_LED_PIN;
   gpio_init(LED_PIN);
   gpio_set_dir(LED_PIN, GPIO_OUT);
-  while (true) {
-    gpio_put(LED_PIN, 1);
-    sleep_ms(5000);
-    gpio_put(LED_PIN, 0);
-    sleep_ms(5000);
-    printf("Hello world: %d\n", ++count);
-  }
+#endif
+
+	// "draw" an horizontal dotted line (?)
+	for (unsigned int c = 0; c < 20; c += 3)
+	{
+		frames[0].data[80 * 64 + 20 + c] = 0x55;
+	}
+	for (unsigned int c = 0; c < 20; c += 3)
+	{
+		frames[0].data[80 * 128 + 20 + c] = 0x99;
+	}
+
+	PIO pio = pio0;
+	uint offset = pio_add_program(pio, &vga_free_run_program);
+	uint sm = pio_claim_unused_sm(pio, true);
+	vga_program_init(pio, sm, offset);
+
+	printf("Welcome.\n");
+
+	while (true)
+	{
+		for (size_t i = 0; i < sizeof(frames[0].data); ++i)
+		{
+			pio_sm_put_blocking(pio, sm, frames[0].data[i]);
+		}
+		printf(".");
+		sleep_ms(1000);
+	}
 }
diff --git a/src/vga.pio b/src/vga.pio
new file mode 100644
index 0000000..e17f1df
--- /dev/null
+++ b/src/vga.pio
@@ -0,0 +1,9 @@
+.program vga_free_run
+
+
+entrypoint:
+    pull
+loop:
+    out pins, 1 [2]
+    jmp loop
+