diff --git a/software/src/io.c b/software/src/io.c
new file mode 100644
index 0000000..1f3c4d5
--- /dev/null
+++ b/software/src/io.c
@@ -0,0 +1,119 @@
+#include <zephyr/kernel.h>
+#include "pin_io.h"
+
+/* LT ADCs work like this:
+ * 1) Send CONV signal high
+ * 2) wait for conversion to happen
+ * 3) read in from output (change on rising edge, read on lower)
+ * The evaluation boards do not give access to the BUSY signal, so this
+ * contoller cannot be interrupt driven. This is probably a blessing
+ * in disguise because it's easier for me to write blocking code :-)
+ */
+
+struct adc_timing {
+	unsigned conv_time;
+	unsigned wid;
+};
+
+enum adc_types {
+	LT2380_24, 
+	LT2328_16,
+	LT2328_18,
+	ADC_TYPES_LEN
+};
+
+uint32_t
+adc_read(int num, enum adc_types ty)
+{
+	uint32_t r = 0;
+	// TODO
+	static const struct time[ADC_TYPES_LEN] = {
+		[LT2380_24] = {0},
+		[LT2328_16] = {0},
+		[LT2328_18] = {0}
+	};
+
+	if (ty < 0 || ty >= ADC_TYPES_LEN) {
+		LOG_ERROR("adc_read got unknown ADC type\n");
+		k_fatal_halt(K_ERR_KERNEL_OOPS);
+	}
+	if (num < 0 || num >= ADC_MAX) {
+		LOG_ERROR("Bad ADC %d\n", num);
+		k_fatal_halt(K_ERR_KERNEL_OOPS);
+	}
+
+	*adc_sck[num] = 0;
+	*adc_conv[num] = 1;
+
+	k_sleep(K_NSEC(T_CONV + T_DSOBUSYL));
+	*adc_conv[num] = 0;
+
+	for (int i = 0; i < time[ty].wid; i++) {
+		r <<= 1;
+		r |= *adc_sdo[num];
+
+		*adc_sck[num] = 1;
+		/* 1 millisecond -> 1 MHz */
+		k_sleep(K_NSEC(500));
+		*adc_sck[num] = 0;
+	}
+
+	return r;
+}
+
+#define DAC_SS(n, v) *dac_ctrl[(n)] |= (v & 1) << 2
+#define DAC_SCK(n, v) *dac_ctrl[(n)] |= (v & 1) << 1
+#define DAC_MOSI(n, v) *dac_ctrl[(n)] |= (v & 1)
+#define DAC_MISO(n) *dac_miso[(n)]
+
+/* Thankfully we only have one type of DAC (for now).
+ * AD DACs are register-based devices. To write to a register,
+ * 1) Set SCK high.
+ * 2) Set SS high in software (SYNC is active-low), wait setup time.
+ * 3) Set SCK low.
+ * 4) Read MISO, write MOSI.
+ * 5) Set SCK high, wait setup time.
+*/
+uint32_t
+dac_write_raw(int n, uint32_t data)
+{
+	uint32_t r = 0;
+	DAC_SCK(n, 1);
+	DAC_SS(n, 1);
+	k_sleep(K_NSEC(10));
+
+	for (int i = 0; i < 20; i++) {
+		DAC_SCK(n, 0);
+		DAC_MOSI(n, data >> 31 & 1);
+		k_sleep(K_NSEC(500));
+
+		r <<= 1;
+		data <<= 1;
+		r |= DAC_MISO(n) & 1;
+		DAC_SCK(n, 1);
+		k_sleep(K_NSEC(500));
+	}
+
+	return r;
+}
+
+void
+dac_write_v(int n, uint32_t v)
+{
+	dac_write_raw(n, (1 << 20) | (v & 0xFFFFF));
+}
+
+int
+dac_init(int n)
+{
+	/* Write to control register. */
+	const uint32_t msg =
+		(1 << 1) // RBUF
+		| (1 << 4) // Binary Offset
+	;
+	dac_write_raw(n, (1 << 21) | msg);
+	// Read from the control register
+	dac_write_raw(n, (1 << 21) | (1 << 23));
+	// Send NOP to read the returned data.
+	return dac_write_raw(n, 0) == msg;
+}