Add PIO TMDS encode to moon example, as a separate build target

software/apps/moon/CMakeLists.txt

@@ -1,6 +1,4 @@
-# Replace TMDS with 10 bit UART (same baud rate):
-# add_definitions(-DDVI_SERIAL_DEBUG=1)
-# add_definitions(-DRUN_FROM_CRYSTAL)
+# First target: executable that uses regular software encode loop
 
 add_executable(moon
 	main.c
@@ -8,14 +6,38 @@ add_executable(moon
 
 target_compile_options(moon PRIVATE -Wall)
 
-target_compile_definitions(moon PRIVATE DVI_VERTICAL_REPEAT=1 DVI_N_TMDS_BUFFERS=3 DVI_MONOCHROME_TMDS)
-
+target_compile_definitions(moon PRIVATE
+	DVI_VERTICAL_REPEAT=1
+	DVI_N_TMDS_BUFFERS=3
+	DVI_MONOCHROME_TMDS
+)
 
 target_link_libraries(moon
 	pico_stdlib
-	pico_multicore
 	libdvi
 )
 
-# create map/bin/hex file etc.
 pico_add_extra_outputs(moon)
+
+
+# Second target (same source): executable that offloads TMDS encode to PIO + DMA
+
+add_executable(moon_pio_encode
+	main.c
+)
+
+target_compile_options(moon_pio_encode PRIVATE -Wall)
+
+target_compile_definitions(moon_pio_encode PRIVATE
+	DVI_VERTICAL_REPEAT=1
+	DVI_N_TMDS_BUFFERS=3
+	DVI_MONOCHROME_TMDS
+	USE_PIO_TMDS_ENCODE
+)
+
+target_link_libraries(moon_pio_encode
+	pico_stdlib
+	libdvi
+)
+
+pico_add_extra_outputs(moon_pio_encode)

software/apps/moon/main.c

@@ -1,18 +1,18 @@
-#include <stdio.h>
-#include <stdlib.h>
 #include "pico/stdlib.h"
-#include "pico/multicore.h"
 #include "hardware/clocks.h"
 #include "hardware/irq.h"
-#include "hardware/sync.h"
-#include "hardware/gpio.h"
 #include "hardware/vreg.h"
 
 #include "dvi.h"
 #include "dvi_serialiser.h"
 #include "common_dvi_pin_configs.h"
+#include "tmds_encode_1bpp.pio.h"
 #include "tmds_encode.h"
 
+// Display a full-resolution 1bpp image. By default this uses the fast 1bpp
+// encode routine from libdvi (which is actually fast enough for bitplaned
+// RGB111). If USE_PIO_TMDS_ENCODE is defined, the TMDS encode can be
+// offloaded to a slower encode loop on a spare state machine.
 
 // Pick one:
 #define MODE_640x480_60Hz
@@ -46,28 +46,56 @@ struct dvi_inst dvi0;
 int main() {
 	vreg_set_voltage(VREG_VSEL);
 	sleep_ms(10);
-	// Run system at TMDS bit clock
 	set_sys_clock_khz(BIT_CLOCK_MHZ * 1000, true);
-
 	setup_default_uart();
 
-	for (int i = DEBUG_PIN0; i < DEBUG_PIN0 + DEBUG_N_PINS; ++i) {
-		gpio_init(i);
-		gpio_set_dir(i, GPIO_OUT);
-	}
-
 	dvi0.timing = &DVI_TIMING;
 	dvi0.ser_cfg = DEFAULT_DVI_SERIAL_CONFIG;
 	dvi_init(&dvi0, next_striped_spin_lock_num(), next_striped_spin_lock_num());
 	dvi_register_irqs_this_core(&dvi0, DMA_IRQ_0);
-	dvi_start(&dvi0);
 
+	// Set up extra SM, and DMA channels, to offload TMDS encode if necessary
+#ifdef USE_PIO_TMDS_ENCODE
+	PIO encode_pio = dvi0.ser_cfg.pio;
+	uint encode_sm = pio_claim_unused_sm(encode_pio, true);
+	tmds_encode_1bpp_init(encode_pio, encode_sm);
+
+	uint dma_chan_put = dma_claim_unused_channel(true);
+	dma_channel_config c = dma_channel_get_default_config(dma_chan_put);
+	channel_config_set_dreq(&c, pio_get_dreq(encode_pio, encode_sm, true));
+	dma_channel_configure(dma_chan_put, &c,
+		&encode_pio->txf[encode_sm],
+		NULL,
+		FRAME_WIDTH / 32,
+		false
+	);
+
+	uint dma_chan_get = dma_claim_unused_channel(true);
+	c = dma_channel_get_default_config(dma_chan_get);
+	channel_config_set_dreq(&c, pio_get_dreq(encode_pio, encode_sm, false));
+	channel_config_set_write_increment(&c, true);
+	channel_config_set_read_increment(&c, false);
+	dma_channel_configure(dma_chan_get, &c,
+		NULL,
+		&encode_pio->rxf[encode_sm],
+		FRAME_WIDTH,
+		false
+	);
+#endif
+
+	dvi_start(&dvi0);
 	while (true) {
 		for (uint y = 0; y < FRAME_HEIGHT; ++y) {
 			const uint32_t *colourbuf = &((const uint32_t*)moon_img)[y * FRAME_WIDTH / 32];
 			uint32_t *tmdsbuf;
 			queue_remove_blocking_u32(&dvi0.q_tmds_free, &tmdsbuf);
+#ifndef USE_PIO_TMDS_ENCODE
 			tmds_encode_1bpp(colourbuf, tmdsbuf, FRAME_WIDTH);
+#else
+			dma_channel_set_read_addr(dma_chan_put, colourbuf, true);
+			dma_channel_set_write_addr(dma_chan_get, tmdsbuf, true);
+			dma_channel_wait_for_finish_blocking(dma_chan_get);
+#endif
 			queue_add_blocking_u32(&dvi0.q_tmds_valid, &tmdsbuf);
 		}
 	}