spi init code

firmware/Makefile

@@ -1,7 +1,7 @@
 DEFINES += -DF_CPU=16000000
-#CFLAGS += -save-temps
+CFLAGS += -save-temps
 
-OBJECTS = usbdrv/usbdrvasm.o  usbdrv/usbdrv.o main.o display.o lcd/lcd.o
+OBJECTS = usbdrv/usbdrvasm.o  usbdrv/usbdrv.o main.o display.o lcd/lcd.o spi.o
 
 
 

firmware/spi.c

@@ -0,0 +1,45 @@
+#include <avr/io.h>
+#include <stdint.h>
+#include <math.h>
+
+
+#include <spi.h>
+
+
+void spi_init(){
+	uint8_t spcr, spsr, d;
+
+	/* calculate clock divisor,
+	 * gcc with optimize will do that calculation compile-time. */
+	uint8_t spi_clock_divisor(){
+		double d; 
+		d = F_CPU / SPI_BAUDRATE;
+		d = ceil((log(d)/log(2))*0.95); // clock needs dividing by 2^d
+										// the 0.95 to avoid ceil issues
+		return d-1;  // the -1 because minimum divisor is /2
+	}
+
+	d = spi_clock_divisor();
+	if(d>7){
+#warning "spi baudrate too slow, cannot be set"
+		d=7;
+	}
+
+	spsr = 0;
+	spsr |=	(d & 1) ? 0 : _BV(SPI2X);
+	spcr = 0 | _BV(SPIE) | _BV(SPE);
+	spcr |= (d & 2) ? _BV(SPR0) : 0;
+	spcr |= (d & 4) ? _BV(SPR1) : 0;
+
+#ifdef SPI_MASTER
+	spcr |= _BV(MSTR);
+#endif		
+
+	SPCR = spcr;
+	SPSR = spsr;
+}
+
+
+
+
+

firmware/spi.h

@@ -0,0 +1,5 @@
+
+
+
+#define SPI_BAUDRATE 1000000
+#define SPI_MASTER 1