--- /dev/null
+/*
+ * Copyright © 2017 Keith Packard <keithp@keithp.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * General Public License for more details.
+ */
+
+#include <ao.h>
+
+/*
+ * ATtiny ADC interface
+ */
+
+uint16_t
+ao_adc_read(uint8_t mux)
+{
+ uint8_t low, high;
+
+ /* Set the mux */
+ ADMUX = mux;
+
+ /* Start conversion */
+ ADCSRA = ((1 << ADEN) |
+ (1 << ADSC) |
+ (0 << ADATE) |
+ (0 << ADIF) |
+ (0 << ADIE) |
+ (0 << ADPS2) |
+ (0 << ADPS1) |
+ (0 << ADPS0));
+
+ /* Await conversion complete */
+ while ((ADCSRA & (1 << ADSC)) != 0)
+ ;
+
+ /* Read low first */
+ low = ADCL;
+ high = ADCH;
+
+ return (((uint16_t) high) << 8) | low;
+}