file_system.nxc

// ex_file_system.nxc
// This program is intended to serve as an introduction to data files on the 
// NXT. It focuses on handling the codes returned by the file system's API 
// calls, which is an important aspect of the API that is all too often 
// neglected by programmers.
// 
// The program deals with a data file describing circles. On each run, it adds 
// a new circle record to the data file. Then it reads in the whole data file 
// and displays all the circles on NXT screen. It creates the data file if 
// doesn't already exist. If you run it several times in seccession, you will 
// fill the data file and get a file-is-full exception.
//
// The data flie created by this program is not visible on the NXT. To delete 
// the file, circles.dat, you can use the NeXT Explorer or the example program 
// ex_delete_data_file.nxc.

byte handle = 0; // file handle

struct movement
{
	int stepA;
	int stepC;
};

void update_movement(movement & m)
{
	m.stepA = MotorRotationCount(OUT_A);
	m.stepC = MotorRotationCount(OUT_C);
}

// Make sure file is closed whether or not file operations succeed or fail.
void shutdown(const int delay)
{
	if (handle) CloseFile(handle);
	// Get user's attention.
	PlayTone(TONE_C5, SEC_1);
	// Give the user time to read screen messages.
	Wait(delay);
	Stop(true);
}

// Display a return code from a file sytem API call on the NXT screen.
void rtn_code_out(const unsigned int code)
{
	/*TextOut(0, LCD_LINE2, "code            ");*/
	// This line was causing issues on non-enhance NXT firmware
	// feel free to uncomment it if you are running the enhanced firmware
	/*TextOut(50, LCD_LINE2, FormatNum("%04x", code));*/
}

// Open the data file for writing.
void open_for_write()
{
	unsigned int file_size = FILE_SIZE;
	handle = 0;
	// Start with the assumptions the file doesn't exist and needs to be created.
	unsigned int rtn_code = CreateFile(FILE_NAME, file_size, handle);
	// If the file already exists, open it with the intent of adding to the data 
	// that is already there.
	if (rtn_code == LDR_FILEEXISTS)
		rtn_code = OpenFileAppend(FILE_NAME, file_size, handle);
	// Return code handling   
	switch (rtn_code)
	{
		case LDR_SUCCESS:
			return;
		case LDR_FILEISFULL:
			TextOut(0, LCD_LINE1, "file is full    ");
			break;
		default:
			// Unanticipated exception. 
			TextOut(0, LCD_LINE1, "write open      ");
			rtn_code_out(rtn_code);
			break;
	}
	shutdown(SEC_8);
}

// Open the data file for reading.
void open_for_read()
{
	unsigned int file_size = FILE_SIZE;
	handle = 0;
	unsigned int rtn_code = OpenFileRead(FILE_NAME, file_size, handle);
	// Return code handling   
	if (rtn_code != LDR_SUCCESS)
	{
		// Unanticipated exception. 
		TextOut(0, LCD_LINE1, "read open       ");
		rtn_code_out(rtn_code);
		shutdown(SEC_8);
	}
}

// Write one circle record to the data file.
void write_recd(const movement recd)
{
	unsigned int rtn_code = Write(handle, recd);
	// Return code handling
	if (rtn_code != LDR_SUCCESS)
	{
		switch (rtn_code)
		{
			case LDR_EOFEXPECTED:
				TextOut(0, LCD_LINE1, "no more space   ");
				/*break;*/
			default:
				// Unanticipated exception. 
				TextOut(0, LCD_LINE1, "Unknown Error");
				rtn_code_out(rtn_code);
				/*break;*/
		}
		shutdown(SEC_8);
	}
}

// Read all the circle records from the data file. Display each circle as it is 
// read.
void play_all(const movement recd, movement &current)
{
	unsigned int rtn_code = Read(handle, recd);
	// rtn_code_out(rtn_code);
	// Return code handling   
	switch (rtn_code)
	{
		while(true)
		{
			case LDR_SUCCESS:
				current.stepA = recd.stepA;
				current.stepC = recd.stepC;
				RotateMotor(OUT_A,75,recd.stepA);
				RotateMotor(OUT_C,75,recd.stepC);
				/*Wait(SEC_2);*/
				break;
			case LDR_ENDOFFILE:
				// No more data to read.
				return;
			default:
				// Unanticipated exception. 
				TextOut(0, LCD_LINE1, "read failed     ");
				rtn_code_out(rtn_code);
				shutdown(SEC_8);
		}
	}
}