diff --git a/firmware/spi.c b/firmware/spi.c
index 1892ee5..74b1e47 100644
--- a/firmware/spi.c
+++ b/firmware/spi.c
@@ -6,6 +6,19 @@
 #include <spi.h>
 
 
+/* SPI framework.
+ *
+ * currently alpha, uses interrupts, single master/single slave operation
+ */
+
+
+uint8_t * volatile spi_writeptr;
+uint8_t * volatile spi_readptr;
+uint8_t volatile spi_writelen;
+uint8_t volatile spi_readlen;
+uint8_t spi_readbuf[SPI_READBUF_LEN];
+
+
 void spi_init(){
 	uint8_t spcr, spsr, d;
 
@@ -25,21 +38,47 @@ void spi_init(){
 		d=7;
 	}
 
+	//TODO: DDRs setzen
+
 	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;
+
+	// initialize interface for ISR:
+	spi_readptr = spi_readbuf;
+	spi_readlen = SPI_READBUF_LEN;
+	spi_writeptr = NULL;
 }
 
 
+// return true on success, false on error
+uint8_t spi_write(uint8_t *data, uint8_t len){
+	if(spi_writeptr != NULL){
+		return 0
+	}
+	spi_writeptr = data;
+	spi_writelen = len;
+	//TODO: handle SS, write out first byte
+	return 1;
+}
+
 
 
+#ifdef SPI_MASTER
+ISR(SPI_vector){
+
 
+
+
+}
+#endif //SPI_MASTER
diff --git a/firmware/spi.h b/firmware/spi.h
index aabdb6f..493f10d 100644
--- a/firmware/spi.h
+++ b/firmware/spi.h
@@ -3,3 +3,4 @@
 
 #define SPI_BAUDRATE 1000000
 #define SPI_MASTER 1
+#define SPI_READBUF_LEN 32