diff --git a/src/avr/gpio.c b/src/avr/gpio.c
index 7a9c5c7cd..330e8d638 100644
--- a/src/avr/gpio.c
+++ b/src/avr/gpio.c
@@ -14,7 +14,7 @@
 
 
 /****************************************************************
- * AVR chip definitions
+ * General Purpose Input Output (GPIO) pins
  ****************************************************************/
 
 #define GPIO(PORT, NUM) (((PORT)-'A') * 8 + (NUM))
@@ -44,6 +44,67 @@ struct gpio_digital_regs {
 #define GPIO2REGS(pin)                                                  \
     ((struct gpio_digital_regs*)READP(digital_regs[GPIO2PORT(pin)]))
 
+struct gpio_out
+gpio_out_setup(uint8_t pin, uint8_t val)
+{
+    if (GPIO2PORT(pin) >= ARRAY_SIZE(digital_regs))
+        goto fail;
+    struct gpio_digital_regs *regs = GPIO2REGS(pin);
+    if (! regs)
+        goto fail;
+    uint8_t bit = GPIO2BIT(pin);
+    irqstatus_t flag = irq_save();
+    regs->out = val ? (regs->out | bit) : (regs->out & ~bit);
+    regs->mode |= bit;
+    irq_restore(flag);
+    return (struct gpio_out){ .regs=regs, .bit=bit };
+fail:
+    shutdown("Not an output pin");
+}
+
+void
+gpio_out_toggle(struct gpio_out g)
+{
+    g.regs->in = g.bit;
+}
+
+void
+gpio_out_write(struct gpio_out g, uint8_t val)
+{
+    irqstatus_t flag = irq_save();
+    g.regs->out = val ? (g.regs->out | g.bit) : (g.regs->out & ~g.bit);
+    irq_restore(flag);
+}
+
+struct gpio_in
+gpio_in_setup(uint8_t pin, int8_t pull_up)
+{
+    if (GPIO2PORT(pin) >= ARRAY_SIZE(digital_regs))
+        goto fail;
+    struct gpio_digital_regs *regs = GPIO2REGS(pin);
+    if (! regs)
+        goto fail;
+    uint8_t bit = GPIO2BIT(pin);
+    irqstatus_t flag = irq_save();
+    regs->out = pull_up > 0 ? (regs->out | bit) : (regs->out & ~bit);
+    regs->mode &= ~bit;
+    irq_restore(flag);
+    return (struct gpio_in){ .regs=regs, .bit=bit };
+fail:
+    shutdown("Not an input pin");
+}
+
+uint8_t
+gpio_in_read(struct gpio_in g)
+{
+    return !!(g.regs->in & g.bit);
+}
+
+
+/****************************************************************
+ * Hardware Pulse Width Modulation (PWM) pins
+ ****************************************************************/
+
 struct gpio_pwm_info {
     volatile void *ocr;
     volatile uint8_t *rega, *regb;
@@ -101,107 +162,6 @@ static const uint8_t pwm_pins[ARRAY_SIZE(pwm_regs)] PROGMEM = {
 #endif
 };
 
-static const uint8_t adc_pins[] PROGMEM = {
-#if CONFIG_MACH_atmega168
-    GPIO('C', 0), GPIO('C', 1), GPIO('C', 2), GPIO('C', 3),
-    GPIO('C', 4), GPIO('C', 5), GPIO('E', 0), GPIO('E', 1),
-#elif CONFIG_MACH_atmega644p
-    GPIO('A', 0), GPIO('A', 1), GPIO('A', 2), GPIO('A', 3),
-    GPIO('A', 4), GPIO('A', 5), GPIO('A', 6), GPIO('A', 7),
-#elif CONFIG_MACH_at90usb1286
-    GPIO('F', 0), GPIO('F', 1), GPIO('F', 2), GPIO('F', 3),
-    GPIO('F', 4), GPIO('F', 5), GPIO('F', 6), GPIO('F', 7),
-#elif CONFIG_MACH_atmega1280 || CONFIG_MACH_atmega2560
-    GPIO('F', 0), GPIO('F', 1), GPIO('F', 2), GPIO('F', 3),
-    GPIO('F', 4), GPIO('F', 5), GPIO('F', 6), GPIO('F', 7),
-    GPIO('K', 0), GPIO('K', 1), GPIO('K', 2), GPIO('K', 3),
-    GPIO('K', 4), GPIO('K', 5), GPIO('K', 6), GPIO('K', 7),
-#endif
-};
-
-#if CONFIG_MACH_atmega168
-static const uint8_t SS = GPIO('B', 2), SCK = GPIO('B', 5), MOSI = GPIO('B', 3);
-#elif CONFIG_MACH_atmega644p
-static const uint8_t SS = GPIO('B', 4), SCK = GPIO('B', 7), MOSI = GPIO('B', 5);
-#elif CONFIG_MACH_at90usb1286 || CONFIG_MACH_atmega1280 || CONFIG_MACH_atmega2560
-static const uint8_t SS = GPIO('B', 0), SCK = GPIO('B', 1), MOSI = GPIO('B', 2);
-#endif
-
-static const uint8_t ADMUX_DEFAULT = 0x40;
-
-
-/****************************************************************
- * gpio functions
- ****************************************************************/
-
-struct gpio_out
-gpio_out_setup(uint8_t pin, uint8_t val)
-{
-    if (GPIO2PORT(pin) >= ARRAY_SIZE(digital_regs))
-        goto fail;
-    struct gpio_digital_regs *regs = GPIO2REGS(pin);
-    if (! regs)
-        goto fail;
-    uint8_t bit = GPIO2BIT(pin);
-    irqstatus_t flag = irq_save();
-    regs->out = val ? (regs->out | bit) : (regs->out & ~bit);
-    regs->mode |= bit;
-    irq_restore(flag);
-    return (struct gpio_out){ .regs=regs, .bit=bit };
-fail:
-    shutdown("Not an output pin");
-}
-
-void gpio_out_toggle(struct gpio_out g)
-{
-    g.regs->in = g.bit;
-}
-
-void
-gpio_out_write(struct gpio_out g, uint8_t val)
-{
-    irqstatus_t flag = irq_save();
-    g.regs->out = val ? (g.regs->out | g.bit) : (g.regs->out & ~g.bit);
-    irq_restore(flag);
-}
-
-struct gpio_in
-gpio_in_setup(uint8_t pin, int8_t pull_up)
-{
-    if (GPIO2PORT(pin) >= ARRAY_SIZE(digital_regs))
-        goto fail;
-    struct gpio_digital_regs *regs = GPIO2REGS(pin);
-    if (! regs)
-        goto fail;
-    uint8_t bit = GPIO2BIT(pin);
-    irqstatus_t flag = irq_save();
-    regs->out = pull_up > 0 ? (regs->out | bit) : (regs->out & ~bit);
-    regs->mode &= ~bit;
-    irq_restore(flag);
-    return (struct gpio_in){ .regs=regs, .bit=bit };
-fail:
-    shutdown("Not an input pin");
-}
-
-uint8_t
-gpio_in_read(struct gpio_in g)
-{
-    return !!(g.regs->in & g.bit);
-}
-
-
-void
-gpio_pwm_write(struct gpio_pwm g, uint8_t val)
-{
-    if (g.size8) {
-        *(volatile uint8_t*)g.reg = val;
-    } else {
-        irqstatus_t flag = irq_save();
-        *(volatile uint16_t*)g.reg = val;
-        irq_restore(flag);
-    }
-}
-
 struct gpio_pwm
 gpio_pwm_setup(uint8_t pin, uint32_t cycle_time, uint8_t val)
 {
@@ -257,6 +217,42 @@ gpio_pwm_setup(uint8_t pin, uint32_t cycle_time, uint8_t val)
     shutdown("Not a valid PWM pin");
 }
 
+void
+gpio_pwm_write(struct gpio_pwm g, uint8_t val)
+{
+    if (g.size8) {
+        *(volatile uint8_t*)g.reg = val;
+    } else {
+        irqstatus_t flag = irq_save();
+        *(volatile uint16_t*)g.reg = val;
+        irq_restore(flag);
+    }
+}
+
+
+/****************************************************************
+ * Analog to Digital Converter (ADC) pins
+ ****************************************************************/
+
+static const uint8_t adc_pins[] PROGMEM = {
+#if CONFIG_MACH_atmega168
+    GPIO('C', 0), GPIO('C', 1), GPIO('C', 2), GPIO('C', 3),
+    GPIO('C', 4), GPIO('C', 5), GPIO('E', 0), GPIO('E', 1),
+#elif CONFIG_MACH_atmega644p
+    GPIO('A', 0), GPIO('A', 1), GPIO('A', 2), GPIO('A', 3),
+    GPIO('A', 4), GPIO('A', 5), GPIO('A', 6), GPIO('A', 7),
+#elif CONFIG_MACH_at90usb1286
+    GPIO('F', 0), GPIO('F', 1), GPIO('F', 2), GPIO('F', 3),
+    GPIO('F', 4), GPIO('F', 5), GPIO('F', 6), GPIO('F', 7),
+#elif CONFIG_MACH_atmega1280 || CONFIG_MACH_atmega2560
+    GPIO('F', 0), GPIO('F', 1), GPIO('F', 2), GPIO('F', 3),
+    GPIO('F', 4), GPIO('F', 5), GPIO('F', 6), GPIO('F', 7),
+    GPIO('K', 0), GPIO('K', 1), GPIO('K', 2), GPIO('K', 3),
+    GPIO('K', 4), GPIO('K', 5), GPIO('K', 6), GPIO('K', 7),
+#endif
+};
+
+static const uint8_t ADMUX_DEFAULT = 0x40;
 
 DECL_CONSTANT(ADC_MAX, 1024);
 
@@ -335,6 +331,18 @@ gpio_adc_cancel_sample(struct gpio_adc g)
 }
 
 
+/****************************************************************
+ * Serial Peripheral Interface (SPI) hardware
+ ****************************************************************/
+
+#if CONFIG_MACH_atmega168
+static const uint8_t SS = GPIO('B', 2), SCK = GPIO('B', 5), MOSI = GPIO('B', 3);
+#elif CONFIG_MACH_atmega644p
+static const uint8_t SS = GPIO('B', 4), SCK = GPIO('B', 7), MOSI = GPIO('B', 5);
+#elif CONFIG_MACH_at90usb1286 || CONFIG_MACH_atmega1280 || CONFIG_MACH_atmega2560
+static const uint8_t SS = GPIO('B', 0), SCK = GPIO('B', 1), MOSI = GPIO('B', 2);
+#endif
+
 void
 spi_config(void)
 {