diff --git a/src/energenie/drv/build_mac b/src/energenie/drv/build_mac
index 1c48dba..948f30c 100755
--- a/src/energenie/drv/build_mac
+++ b/src/energenie/drv/build_mac
@@ -3,18 +3,13 @@
 # build file for Mac use
 
 # build gpio_test
-gcc gpio_test.c gpio_sim.c
+gcc gpio_test.c gpio_sim.c delay_posix.c
 mv a.out gpio_test
 chmod u+x gpio_test
 
 
-
-
-
-
-
 # build spis_test (soft SPI tester)
-##gcc spi_test.c spis_rpi.c gpio_rpi.c
+##gcc spi_test.c spis.c gpio_sim.c delay_posix.c
 ##mv a.out spis_test
 ##chmod u+x spis_test
 
diff --git a/src/energenie/drv/delay.h b/src/energenie/drv/delay.h
new file mode 100644
index 0000000..63bfe1e
--- /dev/null
+++ b/src/energenie/drv/delay.h
@@ -0,0 +1,22 @@
+/* delay.h  04/04/2016  D.J.Whale
+ *
+ * Abstraction for delay routines, as they are often platform specific
+ */
+
+#ifndef _DELAY_H
+#define _DELAY_H
+
+#include "system.h"
+
+//#include <time.h>
+#include <sys/time.h> // Won't work on Arduino
+
+void delay(struct timespec time);
+
+void delaysec(uint8_t secs);
+
+void delayus(unsigned int us);
+
+#endif
+
+/***** END OF FILE *****/
diff --git a/src/energenie/drv/delay_posix.c b/src/energenie/drv/delay_posix.c
new file mode 100644
index 0000000..a5f27a8
--- /dev/null
+++ b/src/energenie/drv/delay_posix.c
@@ -0,0 +1,55 @@
+/* delay_posix.c  04/04/2016  D.J.Whale
+ *
+ * Delay routines for posix compliant standard libraries (not Arduino)
+ */
+
+//#include <time.h>
+#include <sys/time.h>
+
+#include "system.h"
+
+static struct timespec delay_1sec = {1, 0};
+
+
+void delay(struct timespec time)
+{
+  nanosleep(&time, NULL);
+}
+
+
+void delaysec(uint8_t secs)
+{
+  while (secs-- != 0)
+  {
+    delay(delay_1sec);
+  }
+}
+
+
+/* Based on code suggested by Gordon Henderson:
+ * https://github.com/WiringPi/WiringPi/blob/master/wiringPi/wiringPi.c
+ *
+ * Note that his trick of using the hardware timer just didn't work,
+ * and this is the best of a bad bunch. nanosleep() delays at least
+ * 100uS in some cases.
+ */
+
+
+void delayus(unsigned int us)
+{
+  struct timeval tNow, tLong, tEnd;
+
+  gettimeofday(&tNow, NULL);
+  tLong.tv_sec  = us / 1000000;
+  tLong.tv_usec = us % 1000000;
+  timeradd(&tNow, &tLong, &tEnd);
+
+  while (timercmp(&tNow, &tEnd, <))
+  {
+    gettimeofday(&tNow, NULL);
+  }
+}
+
+
+/***** END OF FILE *****/
+
diff --git a/src/energenie/drv/gpio.h b/src/energenie/drv/gpio.h
index eb3229f..2b261fe 100644
--- a/src/energenie/drv/gpio.h
+++ b/src/energenie/drv/gpio.h
@@ -6,7 +6,7 @@
 #ifndef GPIO_H
 #define GPIO_H
 
-typedef unsigned char uint8_t; //TODO which header file defines this?
+#include "system.h"
 
 /***** FUNCTION PROTOTYPES *****/
 
diff --git a/src/energenie/drv/gpio_test.c b/src/energenie/drv/gpio_test.c
index 2ef63ad..1736bb8 100644
--- a/src/energenie/drv/gpio_test.c
+++ b/src/energenie/drv/gpio_test.c
@@ -5,18 +5,14 @@
 #include <stdio.h>
 #include <time.h>
 
+#include "system.h"
 #include "gpio.h"
-
-//TODO this is platform specific (won't work on Arduino?)
-static void delay(struct timespec time)
-{
-  nanosleep(&time, NULL);
-}
-
-static struct timespec delay_1sec = {1, 0};
+#include "delay.h"
 
 
-// To allow platform specific test harnesses
+/* Allows platform specific test harness,
+ * different platforms will have different available GPIO numbers
+ */
 
 #define GPIO_A 2
 #define GPIO_B 3
@@ -33,15 +29,15 @@
   {
     puts("GPIO A");
     gpio_write(GPIO_A, 1);
-    delay(delay_1sec);
+    delaysec(1);
     gpio_write(GPIO_A, 0);
-    delay(delay_1sec);
+    delaysec(1);
 
     puts("GPIO B");
     gpio_write(GPIO_B, 1);
-    delay(delay_1sec);
+    delaysec(1);
     gpio_write(GPIO_B, 0);
-    delay(delay_1sec);
+    delaysec(1);
   }
   return 0;
 }
diff --git a/src/energenie/drv/spi.h b/src/energenie/drv/spi.h
index 7534264..070fbff 100644
--- a/src/energenie/drv/spi.h
+++ b/src/energenie/drv/spi.h
@@ -7,7 +7,7 @@
 
 /***** INCLUDES *****/
 
-//#include <time.h>
+#include "system.h"
 
 
 /***** CONSTANTS *****/
@@ -24,14 +24,14 @@
 
 typedef struct
 {
-  unsigned char cs;
-  unsigned char sclk;
-  unsigned char mosi;
-  unsigned char miso;
+  uint8_t cs;
+  uint8_t sclk;
+  uint8_t mosi;
+  uint8_t miso;
 
-  unsigned char spol;
-  unsigned char cpol;
-  unsigned char cpha;
+  uint8_t spol;
+  uint8_t cpol;
+  uint8_t cpha;
 
   //struct timespec tSettle;
   //struct timespec tHold;
@@ -53,9 +53,9 @@
 
 void spi_deselect(void);
 
-int spi_byte(int txbyte);
+int spi_byte(uint8_t txbyte);
 
-void spi_frame(unsigned char* pTx, unsigned char* pRx, unsigned char count);
+void spi_frame(uint8_t* pTx, uint8_t* pRx, uint8_t count);
 
 void spi_finished(void);
 
diff --git a/src/energenie/drv/spis_rpi.c b/src/energenie/drv/spis_rpi.c
index f77b606..1b82e8a 100644
--- a/src/energenie/drv/spis_rpi.c
+++ b/src/energenie/drv/spis_rpi.c
@@ -7,9 +7,10 @@
 #include <stdio.h>
 #include <stdlib.h>
 //#include <time.h>
-#include <sys/time.h>
+#include <sys/time.h> // Won't work on Arduino
 #include <string.h>
 
+#include "system.h"
 #include "spi.h"
 #include "gpio.h"
 
@@ -35,7 +36,10 @@
  * and this is the best of a bad bunch. nanosleep() delays at least
  * 100uS in some cases.
  */
- 
+
+//TODO: This is raspberry pi specific
+//Put it in a delay.h delay_rpi.h??
+
 static void delayus(unsigned int us)
 {
   struct timeval tNow, tLong, tEnd;
@@ -118,11 +122,11 @@
 }
 
 
-int spi_byte(int txbyte)
+int spi_byte(uint8_t txbyte)
 {
-  int rxbyte = 0;
-  int bitno;
-  int bit ;
+  uint8_t rxbyte = 0;
+  uint8_t bitno;
+  uint8_t bit ;
 
   //TODO: Implement CPHA1
 
@@ -148,10 +152,10 @@
 }
 
 
-void spi_frame(unsigned char* pTx, unsigned char* pRx, unsigned char count)
+void spi_frame(uint8_t* pTx, uint8_t* pRx, uint8_t count)
 {
-  unsigned char tx = 0;
-  unsigned char rx;
+  uint8_t tx = 0;
+  uint8_t rx;
 
   while (count > 0)
   {
diff --git a/src/energenie/drv/system.h b/src/energenie/drv/system.h
new file mode 100644
index 0000000..24f3b2b
--- /dev/null
+++ b/src/energenie/drv/system.h
@@ -0,0 +1,10 @@
+#ifndef _SYSTEM_H
+#define _SYSTEM_H
+
+//TODO which header file defines these?
+
+typedef unsigned char uint8_t;
+
+#endif
+
+/***** END OF FILE *****/