int sendSDCmd ( unsigned char c, unsigned a)
// c command code
// a bte address of data block
{
int i, r;
//enable SD card
enableSD();
// send a command packet (6 bytes)
writeSPI( c | 0x40); //send command
writeSPI( a>>24); //msb of the address
writeSPI( a>>16);
writeSPI( a>>8);
writeSPI( a); //lsb
writeSPI(0x95); //send CMD0 CRC
// now wait for a response, allow to 8 bytes delay
for( i=0; i<8; i++)
{
r=readSPI();
if ( r != 0xFF)
break;
}
return ( r);
// NOTE SDCS is still low!
} // sendSDCmd
// c command code
// a byte address of data block
int sendSDCmd(unsigned char c, unsigned a)
{
int i, r;
// enable SD card
// CS low
enableSD();
// send a comand packet (6 bytes)
writeSPI(c | 0x40); // send command
writeSPI(a>>24); // msb of the address
writeSPI(a>>16);
writeSPI(a>>8);
writeSPI(a); // lsb
writeSPI(0x95); // send CMD0 CRC
// now wait for a response, allow for up to 8 bytes delay
for(i=0; i<8; i++)
{
r = readSPI();
if (r != 0xFF)
break;
}
return (r);
/* return response
FF - timeout
00 - command accepted
01 - command received, card in idle state after RESET
other codes:
bit 0 = Idle state
bit 1 = Erase Reset
bit 2 = Illegal command
bit 3 = Communication CRC error
bit 4 = Erase sequence error
bit 5 = Address error
bit 6 = Parameter error
bit 7 = Always 0
*/
// NOTE CSCD is still low!
} // sendSDCmd
// returns 0 if successful
// E_COMMAND_ACK failed to acknowledge reset command
// E_INIT_TIMEOUT failed to initialize
int initMedia(void)
{
int i, r;
// 1. with the card NOT selected
// Set DI and CS high
disableSD();
// 2. send 74 or more clock cycles to start up
// apply 74 or more clock pulses to SCLK.
// The card will enter its native operating mode and go ready to accept native commands.
for (i=0; i<10; i++)
clockSPI();
// 3. now select the card
enableSD();
//card detection is now in disk_initialize()
return 0;
} // init media
int initMedia( void)
//returns 0 if succesful
// E_COMMAND_ACK failed to acknowledge reset command
// E_INIT_TIMEOUT failed to initialize
{
int i, r;
;
// 1. with the card NOT selected
disableSD();
// 2. send 80 clock cycles start up
for(i=0;i<80;i++)
clockSPI();
// 3. now select the card
enableSD();
// 4. send a single RESET commmand
r = sendSDCmd( RESET, 0);
disableSD();
if ( r != 1) // must return Idle
return E_COMMAND_ACK;
// 5. send repeatedly INIT until Idle terminates
for (i=0; i<I_TIMEOUT; i++)
{
r = sendSDCmd( INIT, 0); disableSD();
if ( !r)
break;
}
if ( i == I_TIMEOUT)
return E_INIT_TIMEOUT; // init timed out
// 6. increase speed
SPI3ACON = 0; // disable the SPI2 module
SPI3ABRG = 0; // Fpb/(2*(0+1)) = 20/2 = 10MHz
SPI3ACON = 0x8120; // re-enable the SPI2 module
return 0;
} //init media
