2 files changed, 19 insertions, 21 deletions
diff --git a/src/avr/gpio.c b/src/avr/gpio.c
index 9919cdd1..3df6e9e8 100644
--- a/src/avr/gpio.c
+++ b/src/avr/gpio.c
@@ -282,27 +282,24 @@ gpio_adc_setup(uint8_t pin)
     shutdown("Not a valid ADC pin");
 }
 
-uint32_t
-gpio_adc_sample_time(void)
-{
-    return (13 + 1) * 128 + 200;
-}
-
 enum { ADC_DUMMY=0xff };
 static uint8_t last_analog_read = ADC_DUMMY;
 
-uint8_t
+// Try to sample a value. Returns zero if sample ready, otherwise
+// returns the number of clock ticks the caller should wait before
+// retrying this function.
+uint32_t
 gpio_adc_sample(struct gpio_adc g)
 {
     if (ADCSRA & (1<<ADSC))
         // Busy
-        return 1;
+        goto need_delay;
     if (last_analog_read == g.chan)
         // Sample now ready
         return 0;
     if (last_analog_read != ADC_DUMMY)
         // Sample on another channel in progress
-        return 1;
+        goto need_delay;
     last_analog_read = g.chan;
 
 #if defined(ADCSRB) && defined(MUX5)
@@ -315,16 +312,11 @@ gpio_adc_sample(struct gpio_adc g)
 
     // start the conversion
     ADCSRA |= 1<<ADSC;
-    return 1;
-}
-
-void
-gpio_adc_clear_sample(struct gpio_adc g)
-{
-    if (last_analog_read == g.chan)
-        last_analog_read = ADC_DUMMY;
+need_delay:
+    return (13 + 1) * 128 + 200;
 }
 
+// Read a value; use only after gpio_adc_sample() returns zero
 uint16_t
 gpio_adc_read(struct gpio_adc g)
 {
@@ -332,6 +324,14 @@ gpio_adc_read(struct gpio_adc g)
     return ADC;
 }
 
+// Cancel a sample that may have been started with gpio_adc_sample()
+void
+gpio_adc_cancel_sample(struct gpio_adc g)
+{
+    if (last_analog_read == g.chan)
+        last_analog_read = ADC_DUMMY;
+}
+
 
 void
 spi_config(void)
diff --git a/src/avr/gpio.h b/src/avr/gpio.h
index e6cbbd32..4eb37204 100644
--- a/src/avr/gpio.h
+++ b/src/avr/gpio.h
@@ -2,7 +2,6 @@
 #define __AVR_GPIO_H
 
 #include <stdint.h>
-#include "compiler.h" // __always_inline
 
 struct gpio_out {
     struct gpio_digital_regs *regs;
@@ -31,10 +30,9 @@ struct gpio_adc {
     uint8_t chan;
 };
 struct gpio_adc gpio_adc_setup(uint8_t pin);
-uint32_t gpio_adc_sample_time(void);
-uint8_t gpio_adc_sample(struct gpio_adc g);
-void gpio_adc_clear_sample(struct gpio_adc g);
+uint32_t gpio_adc_sample(struct gpio_adc g);
 uint16_t gpio_adc_read(struct gpio_adc g);
+void gpio_adc_cancel_sample(struct gpio_adc g);
 
 void spi_config(void);
 void spi_transfer(char *data, uint8_t len);