Please help me understand this code

Projects Programming
1

First of all, I found out that the SS pin on the UNO is 10 (SPI - Arduino Reference).

That mystery solved.

But because I couldnt get SDFat to work, I had to dig through its documents and examples. It has take me hours but some functions it uses are very rare to find something about on the web

First: What is this? There is almost no documentation online for normal users.

// serial output steam
ArduinoOutStream cout(Serial);

Second: COUT and F.

What is cout? And is the F some way to put things in Flash?

// store error strings in flash
#define sdErrorMsg(msg) sd.errorPrint(F(msg));
//------------------------------------------------------------------------------
uint8_t cidDmp() {
  cid_t cid;
  if (!sd.card()->readCID(&cid)) {
    sdErrorMsg("readCID failed");
    return false;
  }
  cout << F("\nManufacturer ID: ");
  cout << hex << int(cid.mid) << dec << endl;
  cout << F("OEM ID: ") << cid.oid[0] << cid.oid[1] << endl;
  cout << F("Product: ");
  for (uint8_t i = 0; i < 5; i++) {
    cout << cid.pnm[i];
  }
  cout << F("\nVersion: ");
  cout << int(cid.prv_n) << '.' << int(cid.prv_m) << endl;
  cout << F("Serial number: ") << hex << cid.psn << dec << endl;
  cout << F("Manufacturing date: ");
  cout << int(cid.mdt_month) << '/';
  cout << (2000 + cid.mdt_year_low + 10 * cid.mdt_year_high) << endl;
  cout << endl;
  return true;
}

Well, take a look at the code below, it seems over complicated to me, no other sketch that I have seen uses this way of coding.

/*
 * This program attempts to initialize an SD card and analyze its structure.
 */
#include <SPI.h>
#include "SdFat.h"
#include "sdios.h"

// Set USE_SDIO to zero for SPI card access. 
#define USE_SDIO 0
/*
 * SD chip select pin.  Common values are:
 *
 * Arduino Ethernet shield, pin 4.
 * SparkFun SD shield, pin 8.
 * Adafruit SD shields and modules, pin 10.
 * Default SD chip select is the SPI SS pin.
 */
const uint8_t SD_CHIP_SELECT = SS;
/*
 * Set DISABLE_CHIP_SELECT to disable a second SPI device.
 * For example, with the Ethernet shield, set DISABLE_CHIP_SELECT
 * to 10 to disable the Ethernet controller.
 */
const int8_t DISABLE_CHIP_SELECT = -1;

#if USE_SDIO
// Use faster SdioCardEX
SdFatSdioEX sd;
// SdFatSdio sd;
#else // USE_SDIO
SdFat sd;
#endif  // USE_SDIO

// serial output steam
ArduinoOutStream cout(Serial);

// global for card size
uint32_t cardSize;

// global for card erase size
uint32_t eraseSize;
//------------------------------------------------------------------------------
// store error strings in flash
#define sdErrorMsg(msg) sd.errorPrint(F(msg));
//------------------------------------------------------------------------------
uint8_t cidDmp() {
  cid_t cid;
  if (!sd.card()->readCID(&cid)) {
    sdErrorMsg("readCID failed");
    return false;
  }
  cout << F("\nManufacturer ID: ");
  cout << hex << int(cid.mid) << dec << endl;
  cout << F("OEM ID: ") << cid.oid[0] << cid.oid[1] << endl;
  cout << F("Product: ");
  for (uint8_t i = 0; i < 5; i++) {
    cout << cid.pnm[i];
  }
  cout << F("\nVersion: ");
  cout << int(cid.prv_n) << '.' << int(cid.prv_m) << endl;
  cout << F("Serial number: ") << hex << cid.psn << dec << endl;
  cout << F("Manufacturing date: ");
  cout << int(cid.mdt_month) << '/';
  cout << (2000 + cid.mdt_year_low + 10 * cid.mdt_year_high) << endl;
  cout << endl;
  return true;
}
//------------------------------------------------------------------------------
uint8_t csdDmp() {
  csd_t csd;
  uint8_t eraseSingleBlock;
  if (!sd.card()->readCSD(&csd)) {
    sdErrorMsg("readCSD failed");
    return false;
  }
  if (csd.v1.csd_ver == 0) {
    eraseSingleBlock = csd.v1.erase_blk_en;
    eraseSize = (csd.v1.sector_size_high << 1) | csd.v1.sector_size_low;
  } else if (csd.v2.csd_ver == 1) {
    eraseSingleBlock = csd.v2.erase_blk_en;
    eraseSize = (csd.v2.sector_size_high << 1) | csd.v2.sector_size_low;
  } else {
    cout << F("csd version error\n");
    return false;
  }
  eraseSize++;
  cout << F("cardSize: ") << 0.000512*cardSize;
  cout << F(" MB (MB = 1,000,000 bytes)\n");

  cout << F("flashEraseSize: ") << int(eraseSize) << F(" blocks\n");
  cout << F("eraseSingleBlock: ");
  if (eraseSingleBlock) {
    cout << F("true\n");
  } else {
    cout << F("false\n");
  }
  return true;
}
//------------------------------------------------------------------------------
// print partition table
uint8_t partDmp() {
  mbr_t mbr;
  if (!sd.card()->readBlock(0, (uint8_t*)&mbr)) {
    sdErrorMsg("read MBR failed");
    return false;
  }
  for (uint8_t ip = 1; ip < 5; ip++) {
    part_t *pt = &mbr.part[ip - 1];
    if ((pt->boot & 0X7F) != 0 || pt->firstSector > cardSize) {
      cout << F("\nNo MBR. Assuming Super Floppy format.\n");
      return true;
    }
  }
  cout << F("\nSD Partition Table\n");
  cout << F("part,boot,type,start,length\n");
  for (uint8_t ip = 1; ip < 5; ip++) {
    part_t *pt = &mbr.part[ip - 1];
    cout << int(ip) << ',' << hex << int(pt->boot) << ',' << int(pt->type);
    cout << dec << ',' << pt->firstSector <<',' << pt->totalSectors << endl;
  }
  return true;
}
//------------------------------------------------------------------------------
void volDmp() {
  cout << F("\nVolume is FAT") << int(sd.vol()->fatType()) << endl;
  cout << F("blocksPerCluster: ") << int(sd.vol()->blocksPerCluster()) << endl;
  cout << F("clusterCount: ") << sd.vol()->clusterCount() << endl;
  cout << F("freeClusters: ");
  uint32_t volFree = sd.vol()->freeClusterCount();
  cout <<  volFree << endl;
  float fs = 0.000512*volFree*sd.vol()->blocksPerCluster();
  cout << F("freeSpace: ") << fs << F(" MB (MB = 1,000,000 bytes)\n");
  cout << F("fatStartBlock: ") << sd.vol()->fatStartBlock() << endl;
  cout << F("fatCount: ") << int(sd.vol()->fatCount()) << endl;
  cout << F("blocksPerFat: ") << sd.vol()->blocksPerFat() << endl;
  cout << F("rootDirStart: ") << sd.vol()->rootDirStart() << endl;
  cout << F("dataStartBlock: ") << sd.vol()->dataStartBlock() << endl;
  if (sd.vol()->dataStartBlock() % eraseSize) {
    cout << F("Data area is not aligned on flash erase boundaries!\n");
    cout << F("Download and use formatter from www.sdcard.org!\n");
  }
}
2

PArt 2

//------------------------------------------------------------------------------
void setup() {
  Serial.begin(9600);
  
  // Wait for USB Serial 
  while (!Serial) {
    SysCall::yield();
  }

  // use uppercase in hex and use 0X base prefix
  cout << uppercase << showbase << endl;

  // F stores strings in flash to save RAM
  cout << F("SdFat version: ") << SD_FAT_VERSION << endl;
#if !USE_SDIO  
  if (DISABLE_CHIP_SELECT < 0) {
    cout << F(
           "\nAssuming the SD is the only SPI device.\n"
           "Edit DISABLE_CHIP_SELECT to disable another device.\n");
  } else {
    cout << F("\nDisabling SPI device on pin ");
    cout << int(DISABLE_CHIP_SELECT) << endl;
    pinMode(DISABLE_CHIP_SELECT, OUTPUT);
    digitalWrite(DISABLE_CHIP_SELECT, HIGH);
  }
  cout << F("\nAssuming the SD chip select pin is: ") <<int(SD_CHIP_SELECT);
  cout << F("\nEdit SD_CHIP_SELECT to change the SD chip select pin.\n");
#endif  // !USE_SDIO  
}
//------------------------------------------------------------------------------
void loop() {
  // Read any existing Serial data.
  do {
    delay(10);
  } while (Serial.available() && Serial.read() >= 0);

  // F stores strings in flash to save RAM
  cout << F("\ntype any character to start\n");
  while (!Serial.available()) {
    SysCall::yield();
  }

  uint32_t t = millis();
#if USE_SDIO
  if (!sd.cardBegin()) {
    sdErrorMsg("\ncardBegin failed");
    return;
  }
#else  // USE_SDIO
  // Initialize at the highest speed supported by the board that is
  // not over 50 MHz. Try a lower speed if SPI errors occur.
  if (!sd.cardBegin(SD_CHIP_SELECT, SD_SCK_MHZ(50))) {
    sdErrorMsg("cardBegin failed");
    return;
  }
 #endif  // USE_SDIO 
  t = millis() - t;

  cardSize = sd.card()->cardSize();
  if (cardSize == 0) {
    sdErrorMsg("cardSize failed");
    return;
  }
  cout << F("\ninit time: ") << t << " ms" << endl;
  cout << F("\nCard type: ");
  switch (sd.card()->type()) {
  case SD_CARD_TYPE_SD1:
    cout << F("SD1\n");
    break;

  case SD_CARD_TYPE_SD2:
    cout << F("SD2\n");
    break;

  case SD_CARD_TYPE_SDHC:
    if (cardSize < 70000000) {
      cout << F("SDHC\n");
    } else {
      cout << F("SDXC\n");
    }
    break;

  default:
    cout << F("Unknown\n");
  }
  if (!cidDmp()) {
    return;
  }
  if (!csdDmp()) {
    return;
  }
  uint32_t ocr;
  if (!sd.card()->readOCR(&ocr)) {
    sdErrorMsg("\nreadOCR failed");
    return;
  }
  cout << F("OCR: ") << hex << ocr << dec << endl;
  if (!partDmp()) {
    return;
  }
  if (!sd.fsBegin()) {
    sdErrorMsg("\nFile System initialization failed.\n");
    return;
  }
  volDmp();
}
3

F is a macro that is used to store constant strings in flash memory instead of RAM.

Arduino Reference PROGMEM (see end of page)

cout is a global object to a stream buffer.

https://en.cppreference.com/w/cpp/io/cout

4

Thank you.

But why is he using streams? Can you explain a little bit of what he is doing in these scripts?

5

cout is usually relevant when code executes in a unix-like environment with stdout, stderr, and stdin.

6

PaulMurrayCbr:
cout is usually relevant when code executes in a unix-like environment with stdout, stderr, and stdin.

Ok, but than again; this is C++ with Arduino.

What is he doing in this sketch? Should or shouldnt I use this in my dataloggers?

Most people say that SDfat is better than SD but if I cannot understand why and what it is doing, i cannot implement.

7

A little outside my area of expertise to be able to properly explain it, but in layman's terms

cout is an instance of ArduinoOutStream. You will need to study the latter.

cout << something simply sends data to the defined output, in your code Serial.

8

Thanks. I tried to understand that ArduinoOutStream but it is out of my leaque for now. Wonder why they use it in their examples. It can be so much easier.