Use SPI to send commands to the WS2801 strip

Makefile

@@ -7,7 +7,7 @@ LD=gcc
 
 # default build configuration
 # "make BUILD=release" does a release build
-BUILD:=release
+BUILD:=debug
 
 # basic build flags configuration
 CFLAGS+=-std=c99 -Wall -pedantic -Wno-long-long -D_POSIX_C_SOURCE=20120607L -D_FILE_OFFSET_BITS=64

src/ws2801.c

@@ -3,76 +3,77 @@
 #include <malloc.h>
 #include <errno.h>
 
-#include <wiringPi.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <sys/ioctl.h>
+#include <sys/types.h>
+#include <linux/spi/spidev.h>
+
+//#include <wiringPi.h>
 
 #include "../include/logger.h"
 #include "../include/ws2801.h"
 
-#define WS2801_CLK_GPIO 17
+static const char    *spi_dev   = "/dev/spidev0.0";
-#define WS2801_DAT_GPIO 18
+static const uint32_t spi_speed = 250000; // clock freq in Hz
+static const uint16_t spi_delay = 0; // us
+static const uint8_t  spi_bits  = 8; // bits per word
 
-// the interface rpi->ws2801 is active low
-#define BUS_HIGH LOW
-#define BUS_LOW  HIGH
-
-uint8_t *modRed = NULL;
-uint8_t *modGreen = NULL;
-uint8_t *modBlue = NULL;
 uint8_t  numModules;
+uint8_t *message;
 
-void busy_wait(void)
+int spi_fd = 0;
+
+void send_message(void)
 {
-	static const struct timespec bitsleep = {0, 1000};
+	struct spi_ioc_transfer tr = {
-	nanosleep(&bitsleep, NULL);
+		.tx_buf = (unsigned long)message,
+		.rx_buf = (unsigned long)NULL,
+		.len = 3 * numModules,
+		.delay_usecs = spi_delay,
+		.speed_hz = spi_speed,
+		.bits_per_word = 8
+	};
+
+	if(ioctl(spi_fd, SPI_IOC_MESSAGE(1), &tr) < 0) {
+		LOG(LVL_ERR, "ws2801: could not send SPI message: %s", strerror(errno));
 	}
-
-void send_bit(uint8_t value)
-{
-	digitalWrite(WS2801_DAT_GPIO, (value ? BUS_HIGH : BUS_LOW));
-
-	digitalWrite(WS2801_CLK_GPIO, BUS_LOW);
-	busy_wait();
-
-	// rising edge at clock
-	digitalWrite(WS2801_CLK_GPIO, BUS_HIGH);
-	busy_wait();
-}
-
-void send_commit_condition(void)
-{
-	digitalWrite(WS2801_DAT_GPIO, BUS_LOW);
-	digitalWrite(WS2801_CLK_GPIO, BUS_LOW);
-}
-
-void send_byte(uint8_t byte)
-{
-	for(int i = 0; i <= 7; i++) {
-		send_bit(byte & 0x1);
-		byte >>= 1;
-	}
-}
-
-void send_colour(uint8_t red, uint8_t green, uint8_t blue)
-{
-	send_byte(red);
-	send_byte(green);
-	send_byte(blue);
 }
 
 int ws2801_init(uint8_t nMod)
 {
-	if(wiringPiSetupGpio() == -1) {
+	// Initialize SPI
-		LOG(LVL_FATAL, "ws2801: wiringPi setup failed: %s", strerror(errno));
+	// We need to have stable data at falling edge of the spi interface (this
+	// means rising edge at the led strip, as the signal is inverted.
+	uint8_t spi_mode = SPI_NO_CS | SPI_CPOL;
+
+	spi_fd = open(spi_dev, O_RDWR);
+	if(spi_fd < 0) {
+		LOG(LVL_ERR, "ws2801: cannot open %s: %s", spi_dev, strerror(errno));
 		return -1;
 	}
 
-	numModules = nMod;
+	if(ioctl(spi_fd, SPI_IOC_WR_MODE, &spi_mode) == -1) {
-	modRed = malloc(nMod * sizeof(uint8_t));
+		LOG(LVL_ERR, "ws2801: cannot change SPI mode: %s", strerror(errno));
-	modGreen = malloc(nMod * sizeof(uint8_t));
+		return -1;
-	modBlue = malloc(nMod * sizeof(uint8_t));
+	}
 
-	if(!modRed || !modGreen || !modBlue) {
+	if(ioctl(spi_fd, SPI_IOC_WR_BITS_PER_WORD, &spi_bits) == -1) {
-		LOG(LVL_ERR, "ws2801: could not allocate all colour arrays!");
+		LOG(LVL_ERR, "ws2801: cannot change SPI bits per word: %s", strerror(errno));
+		return -1;
+	}
+
+	if(ioctl(spi_fd, SPI_IOC_WR_MAX_SPEED_HZ, &spi_speed) == -1) {
+		LOG(LVL_ERR, "ws2801: cannot change SPI speed: %s", strerror(errno));
+		return -1;
+	}
+
+	// create the message array
+	numModules = nMod;
+	message = malloc(3 * nMod * sizeof(uint8_t));
+
+	if(!message) {
+		LOG(LVL_ERR, "ws2801: could not allocate the message array!");
 		return -1;
 	}
 
@@ -81,25 +82,21 @@ int ws2801_init(uint8_t nMod)
 
 void ws2801_shutdown(void)
 {
-	if(modRed != NULL) { free(modRed); modRed = NULL; }
+	close(spi_fd);
-	if(modGreen != NULL) { free(modGreen); modGreen = NULL; }
+
-	if(modBlue != NULL) { free(modBlue); modBlue = NULL; }
+	if(message != NULL) { free(message); message = NULL; }
 }
 
 void ws2801_set_colour(uint8_t module, uint8_t red, uint8_t green, uint8_t blue)
 {
-	modRed[module] = red;
+	message[3*module + 0] = ~red;
-	modGreen[module] = green;
+	message[3*module + 1] = ~green;
-	modBlue[module] = blue;
+	message[3*module + 2] = ~blue;
 }
 
 void ws2801_send_update(void)
 {
-	for(uint8_t i = 0; i < numModules; i++) {
+	send_message();
-		send_colour(modRed[i], modGreen[i], modBlue[i]);
-	}
-
-	send_commit_condition();
 
 	static const struct timespec sleepval = {0, 550000};
 	nanosleep(&sleepval, NULL);