Testing sdcard initialization with Arduino

arduino/sdcard-test/sdcard-test.ino

@@ -0,0 +1,113 @@
+/**
+ * SPI SD-Card test sketch
+ * Reads the first 128 bytes from cf and prints it out as ascii characters in serial monitor at 9200 baud
+ * 
+ * Implementation of the specification at http://elm-chan.org/docs/mmc/mmc_e.html
+ */
+
+#define CS 5    // aka CAT3
+#define MOSI 4  // aka DI or CMD
+#define SCK 3   // aka CAT3
+#define MISO 2  // aka DAT0
+
+void setup() {
+  pinMode(CS, OUTPUT);
+  pinMode(MOSI, OUTPUT);
+  pinMode(SCK, OUTPUT);
+  pinMode(MISO, INPUT);
+
+  Serial.begin(9600);
+
+  /***** Init sequence *******/
+
+  // Wait 1ms
+  delay(1);
+
+  Serial.println("Init card...");
+
+
+  // >= 75 clocks with CS and DI high
+  digitalWrite(CS, HIGH);
+  digitalWrite(MOSI, HIGH);
+  for (byte i=0; i<80; i++) {
+    clk();
+  }
+
+  // CMD0 with CS low (Software reset). Means "Leave native mode and enter SPI mode"
+  digitalWrite(CS, LOW);
+  sendCommand(B01000000); // First two bits are always 01. Command is 0 (000000).
+  byte resp = receiveResponse();
+  Serial.println("Card response:");
+  Serial.println(resp, HEX);
+  digitalWrite(CS, HIGH);
+
+}
+
+void loop() {}
+
+/**
+ * Sends a clock cycle
+ */
+void clk() {
+  digitalWrite(SCK, HIGH);
+  //delayMicroseconds(1);
+  digitalWrite(SCK, LOW);
+  //delayMicroseconds(1);
+}
+
+/**
+ * Sends a command to card.
+ * The sent CRC field is valid for the CMD0 message.
+ * This is ok, since the CRC field will not be checked in SPI mode.
+ * @param index: the command index byte. First two bytes are the sync bytes "01".
+ */
+void sendCommand(byte index) {
+  // Send command index (2+6=8 bits)
+  sendByte(index);
+  // Send argument (32 bit)
+  for(byte i=0; i<4; i++) {
+    sendByte(0);
+  }
+  // Send CRC with final stop bit (7+1=8 bits)
+  sendByte(B10010101);  // We send always the CMD0 CRC, because is not checked in SPI mode
+}
+
+/**
+ * Sends a byte to the card. The two MSB must be 01 as per specification.
+ * Byte is sent MSB first.
+ */
+void sendByte(byte b) {
+  for (byte i=0; i<8; i++) {
+    // If last bit is 1 set MOSI HIGH, else LOW
+    digitalWrite(MOSI, (b & B10000000) == B10000000 ? HIGH : LOW);
+    clk();
+    // Shift byte to have, in the next cycle, the next bit in last position
+    b = b << 1;
+  }
+}
+
+/**
+ * Receives the response from card
+ * MSB first.
+ */
+byte receiveResponse() {
+  digitalWrite(CS, LOW);
+  digitalWrite(MOSI, HIGH);
+  
+  // continuously toggle the SD CLK signal and observe the MISO line for data:
+  // message response starts with 0
+  while (digitalRead(MISO)) {
+    clk();
+  }  // Wait for first 0
+
+  byte resp = 0;
+  // Read 8 bits
+  for (byte i=0; i<8; i++) {
+    if (digitalRead(MISO)) {
+      resp = resp | B00000001;
+    }
+    resp = resp << 1;
+    clk();
+  }
+  
+}