diff --git a/src/main.c b/src/main.c
index 5cf7b74..ba61297 100644
--- a/src/main.c
+++ b/src/main.c
@@ -131,6 +131,17 @@ void set_pixel(uint16_t x, uint16_t y)
 	frames[0].data[y * 80 + x / 8] |= (1 << x % 8);
 }
 
+/**
+ * @brief Represents a program running on the SM of a PIO.
+ *
+ */
+typedef struct PIORun
+{
+	PIO pio;     //< executing PIO
+	uint offset; //< PIO memory offset for program
+	uint sm;     //< executing SM
+} PIORun;
+
 int main()
 {
 	setup_clocks();
@@ -139,6 +150,7 @@ int main()
 
 	// clear frame buffer
 	memset(&frames[0].data[0], 0, sizeof(frames[0].data));
+	// draw a cross
 	// horizontal lines
 	for (uint16_t x = 0; x < 640; ++x)
 	{
@@ -154,47 +166,52 @@ int main()
 		set_pixel(640, y);
 	}
 
-	// PIO and state machines
-	PIO pio = pio0;
+	// Running programs on PIO
+	PIORun vga_hsync, vga_vsync, vga_pixel;
+	vga_hsync.pio = vga_vsync.pio = vga_pixel.pio = pio0;
 
 	// Prepare frame interrupt
-	pio_set_irq1_source_enabled(pio, pis_interrupt1, true);
-	irq_set_exclusive_handler(PIO0_IRQ_1, new_frame_handler);
-	irq_set_enabled(PIO0_IRQ_1, true);
+	// Frame interrupt is asserted on PIO0 interrupt 1 by SM1
+	pio_set_irq1_source_enabled(vga_vsync.pio, pis_interrupt1,
+	                            true); // allow SM1 of PIO to fire the interrupt
+	irq_set_exclusive_handler(PIO0_IRQ_1, new_frame_handler); // set handler for IRQ1 of PIO
+	irq_set_enabled(PIO0_IRQ_1, true);                        // enable interrupt
 
 	// VGA HSYNC program
-	uint offset1 = pio_add_program(pio, &vga_hsync_program);
-	uint sm1 = pio_claim_unused_sm(pio, true);
-	printf("Starting VGA hsync machine on %u...\n", sm1);
-	vga_hsync_program_init(pio, sm1, offset1);
-	printf("Feeding horizontal sync...\n");
+	printf("Starting VGA hsync machine... ");
+	if (!pio_can_add_program(vga_hsync.pio, &vga_hsync_program))
+		panic("cannot add program");
+	vga_hsync.offset = pio_add_program(vga_hsync.pio, &vga_hsync_program);
+	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(pio, sm1, (64 - 1) * 4);
-	pio_sm_put_blocking(pio, sm1, (776 - 1) * 4);
+	pio_sm_put_blocking(vga_hsync.pio, vga_hsync.sm, (64 - 1) * 4);
+	pio_sm_put_blocking(vga_hsync.pio, vga_hsync.sm, (776 - 1) * 4);
+	printf("OK\n");
 
 	// 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");
+	printf("Starting VGA vsync machine... ");
+	if (!pio_can_add_program(vga_vsync.pio, &vga_vsync_program))
+		panic("cannot add program");
+	vga_vsync.offset = pio_add_program(vga_vsync.pio, &vga_vsync_program);
+	vga_vsync.sm = pio_claim_unused_sm(vga_vsync.pio, true);
+	vga_vsync_program_init(vga_vsync.pio, vga_vsync.sm, vga_vsync.offset);
 	// low pulse assert lasts for 3 horizontal lines, then adjust by one
-	pio_sm_put_blocking(pio, sm2, 3 - 1);
-	pio_sm_put_blocking(pio, sm2, 500 - 3 - 1);
+	pio_sm_put_blocking(vga_vsync.pio, vga_vsync.sm, 3 - 1);
+	pio_sm_put_blocking(vga_vsync.pio, vga_vsync.sm, 500 - 3 - 1);
 	printf("OK\n");
 
 	// VGA pixel program
+	printf("Starting VGA pixel machine... ");
+	if (!pio_can_add_program(vga_pixel.pio, &vga_free_run_program))
+		panic("cannot add program");
+	vga_pixel.offset = pio_add_program(vga_pixel.pio, &vga_free_run_program);
+	vga_pixel.sm = pio_claim_unused_sm(vga_pixel.pio, false);
+	vga_pixel_program_init(vga_pixel.pio, vga_pixel.sm, vga_pixel.offset);
+	pio_sm_put_blocking(vga_pixel.pio, vga_pixel.sm, 640 - 1);
+	printf("OK\n");
 
-	printf("pio_add_program...\n");
-	uint offset0 = pio_add_program(pio, &vga_free_run_program);
-	printf("pio_claim_unused_sm...\n");
-	uint sm0 = pio_claim_unused_sm(pio, false);
-	printf("sm0 = %u\n", sm0);
-	printf("Starting VGA pixel machine on %u...\n", sm0);
-	vga_pixel_program_init(pio, sm0, offset0);
-	pio_sm_put_blocking(pio, sm0, 640 - 1);
-
-	printf("Setting up DMA...\n");
+	printf("Setting up DMA... ");
 	dma_channel = dma_claim_unused_channel(true);
 	dma_channel_config dma_config = dma_channel_get_default_config(dma_channel);
 	channel_config_set_transfer_data_size(&dma_config, DMA_SIZE_32);
@@ -211,8 +228,9 @@ int main()
 	                      false);
 
 	dma_ready = true;
+	printf("OK\n");
 
-	printf("Start!\n");
+	printf("Now running.\n");
 
 	for (;;)
 		tight_loop_contents();