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