tornado/: use UART in SPI mode to send LED patterns (at 4 Mbps)

tornado/fw/Makefile

@@ -31,7 +31,7 @@ OBJCOPY = $(AVR_PREFIX)objcopy
 #OBJDUMP = $(AVR_PREFIX)objdump
 SIZE = $(AVR_PREFIX)size
 
-OBJS = $(NAME).o $(COMMON_OBJS)
+OBJS = $(NAME).o led.o $(COMMON_OBJS)
 BOOT_OBJS = boot.o $(COMMON_OBJS)
 COMMON_OBJS =
 

tornado/fw/led.c

@@ -0,0 +1,82 @@
+/*
+ * fw/led.c - LED control
+ *
+ * Written 2012 by Werner Almesberger
+ * Copyright 2012 Werner Almesberger
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+
+#include <stdint.h>
+
+#include <avr/io.h>
+#include <avr/interrupt.h>
+#define F_CPU	8000000UL
+#include <util/delay.h>
+
+#include "io.h"
+#include "led.h"
+
+
+void led_show(const uint8_t p[LED_BYTES])
+{
+	uint8_t i;
+
+	for (i = 0; i != 8; i++) {
+		while (!(UCSR0A & (1 << UDRE0)));
+		UDR0 = p[i];
+	}
+
+	/*
+	 * There doesn't seem to be any reliable way to synchronize with the
+	 * end of the shift operation register that wouldn't cli/sei. Note
+	 * that, since the receiver is disabled, we can't use the RX side for
+	 * this purpose (as it is done in the atusb firmware).
+	 *
+	 * So instead we just wait for the worst-case delay, being one byte
+	 * in the shift register and another byte in the transmit buffer,
+	 * giving a total of 16 bits.
+	 *
+	 * This is a bit too pessimistic and produces a slight extra delay of
+	 * about 1.8 us. (The whole pattern transmission takes 16 us.)
+	 * See also ../doc/lclk-1123.png
+	 */
+
+	_delay_us(4);	/* 16 bits at 4 MHz */
+	SET(LED_LCLK);
+	CLR(LED_LCLK);
+}
+
+
+void led_off(void)
+{
+	static uint8_t zero[LED_BYTES];
+
+	led_show(zero);    
+}
+
+
+void led_init(void)
+{
+	CLR(LED_SCLK);
+	OUT(LED_SCLK);
+	CLR(LED_LCLK);
+	OUT(LED_LCLK);
+
+	UBRR0 = 0;		/* maximum data rate */
+	UCSR0C =
+	    1 << UMSEL01 |	/* Master SPI */
+	    1 << UMSEL00 | 
+	    1 << UDORD0 |	/* MSB first */
+	    0 << UCPHA0 |	/* SPI Mode 0 */
+	    0 << UCPOL0;
+	UCSR0B =
+	    1 << TXEN0;		/* enable transmitter */
+	UBRR0 = 0;		/* the manual sez we need this */
+
+	led_off();
+}

tornado/fw/led.h

@@ -0,0 +1,28 @@
+/*
+ * fw/led.h - LED control
+ *
+ * Written 2012 by Werner Almesberger
+ * Copyright 2012 Werner Almesberger
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+
+#ifndef LED_H
+#define LED_H
+
+#include <stdint.h>
+
+
+#define	N_LEDS		64
+#define	LED_BYTES	(N_LEDS/8)
+
+
+void led_show(const uint8_t p[LED_BYTES]);
+void led_off(void);
+void led_init(void);
+
+#endif /* !LED_H */

tornado/fw/tornado.c

@@ -5,6 +5,7 @@
 #include <util/delay.h>
 
 #include "io.h"
+#include "led.h"
 
 
 #define	HIGH(port) \
@@ -38,9 +39,6 @@
 #endif
 
 
-#define	N_LEDS	64
-
-
 static void send(uint8_t pattern[N_LEDS/8])
 {
 	uint8_t i, j, mask;
@@ -96,7 +94,7 @@ static uint16_t adc(bool x)
 
 int main(void)
 {
-	static uint8_t p[N_LEDS/8];
+	static uint8_t p[LED_BYTES];
 	uint8_t mode = 0;
 	uint16_t n = 0, v;
 
@@ -119,6 +117,7 @@ int main(void)
 	OUT(VDD);
 #endif
 
+	led_init();
 
 	while (1) {
 		while (!PIN(SW_SW));
@@ -149,9 +148,9 @@ int main(void)
 				p[(v >> 3) & 7] &= ~(1 << (v & 7));
 			else
 				p[(v >> 3) & 7] |= 1 << (v & 7);
-			send(p);
+			led_show(p);
 			n++;
 		}
-		_delay_ms(1);
+		_delay_ms(100);
 	}
 }