Started rewrite for using an I2S amplifier with less unnecessary features.

src/spi_master.cpp

@@ -0,0 +1,26 @@
+#include "spi_master.h"
+#include <Arduino.h>
+#include "esmp3.h"
+
+void SPIMaster::initialize() {
+	pinMode(PIN_CS_SD, OUTPUT);
+	pinMode(PIN_CS_RFID, OUTPUT);
+	disable_all();
+}
+
+void SPIMaster::disable_all() {
+	digitalWrite(PIN_CS_SD, HIGH);
+	digitalWrite(PIN_CS_RFID, HIGH);
+}
+
+void SPIMaster::enable_rfid() {
+	disable_all();
+	digitalWrite(PIN_CS_RFID, LOW);
+	delay(5);
+}
+
+void SPIMaster::enable_sd() {
+	disable_all();
+	digitalWrite(PIN_CS_SD, LOW);
+	delay(5);
+}