add voltage test loop

src/main.cpp

@@ -26,6 +26,7 @@
 #define MIDI_NOTE_LENGTH 61
 
 #define MAX_DAC_INPUT 4095 // 2^12 - 1
+#define TEST_DELAY 5 // seconds to sleep in the test loop
 
 
 void
@@ -74,6 +75,19 @@ loopMIDI(alsa_sequencer* seq, spi_connection* spi)
 	}
 }
 
+void
+loopTestVoltages(spi_connection* spi)
+{
+	u32 zero_volts = 0;
+	u32 one_volt = 816;
+
+	for (u32 i = 0;; i++) {
+		u32 volts = (i % 2 == 0) ? zero_volts : one_volt;
+		spiSendVoltage(spi, volts);
+		sleep(TEST_DELAY);
+	}
+}
+
 i32
 main(i32 argc, char* argv[])
 {
@@ -109,7 +123,7 @@ main(i32 argc, char* argv[])
 				loopMIDI(&seq, &spi);
 				break;
 			case 't':
-				printf("TODO: cycle test voltages to SPI DAC\n");
+				loopTestVoltages(&spi);
 				break;
 			case 'h':
 			default: