So many articles on the web for PIC micros and Arduino. I finally went back to something that worked. Kinda. I never actually used the write feature of Petitfatfs before but it has been said to work. Looking in the mmc.c code for Petitfatfs I saw what I believed could be made into a FAT agnostic working example, assuming you already have the starting sector for your file and you want to replace the first 512 bytes of it. I have no provisions here for moving to different areas of the file. Perhaps you could use sdCardSkipBytes() for that after figuring out how many sectors in your file you will need to go. That is how I do it with SimpleSD now.
I pulled from these parts, all fortunately in the mmc.c file:
- disk_writep()
- send_cmd()
- rcv_spi()
- xmit_spi()
- #define CMD24 (0x40+24) /* WRITE_BLOCK */
- #define SELECT() PORTD &= ~(1<<6) /* CS=low */
- #define DESELECT() PORTD |= (1<<6) /* CS=high */
Of course, without sdCardFindFileFirstSector() from SimpleSD I wouldn't be able to use these write functions. I've tested this with a few different strings on the emulator (Emscripten CUzeBox) and some real Uzebox hardware. Seems to work as expected.
NOTE: I put the code together from existing code within PFF. This is a minimal example and all that I think I will need.
Code: Select all
// Portions of code here part of PFF, (C)ChaN, 2010
#define CMD24 (0x40+24) /* WRITE_BLOCK */
#define SELECT() PORTD &= ~(1<<6) /* CS=low */
#define DESELECT() PORTD |= (1<<6) /* CS=high */
/* Returns received data */
unsigned char rcv_spi (void){
SPDR = 0xff;
loop_until_bit_is_set(SPSR, SPIF);
return SPDR;
}
/* Exchange a byte */
/* Returns received data */
/* Data to be sent */
void xmit_spi ( unsigned char dat ) {
SPDR = dat;
loop_until_bit_is_set(SPSR, SPIF);
}
u8 SD_Command( u8 cmd, unsigned long arg ){
unsigned char n, res;
/* Select the card */
DESELECT();
rcv_spi();
SELECT();
rcv_spi();
/* Send a command packet */
xmit_spi(cmd); /* Start + Command index */
xmit_spi((unsigned char)(arg >> 24)); /* Argument[31..24] */
xmit_spi((unsigned char)(arg >> 16)); /* Argument[23..16] */
xmit_spi((unsigned char)(arg >> 8)); /* Argument[15..8] */
xmit_spi((unsigned char)arg); /* Argument[7..0] */
n = 0x01; /* Dummy CRC + Stop */
xmit_spi(n);
/* Wait for a valid response in timeout of 10 attempts */
n = 10;
/* Receive a command response */
do {
res = rcv_spi();
} while ((res & 0x80) && --n);
/* Return with the response value */
return res;
}
u8 SD_WriteSector( unsigned long SectorNumber, u8 *buff ){
u8 i;
unsigned int wc;
unsigned int count;
/* send block-write command... */
for(u8 i=0; i<8; i++){xmit_spi( 0xFF );}
SD_Command( CMD24, SectorNumber << 9);
xmit_spi(0xFF); xmit_spi(0xFE); /* Data block header */
wc = 512;
while(wc--){ xmit_spi(*buff++); }
// Deselect the card.
DESELECT();
}Code: Select all
u8 testar_index=0;
u8 testar[] = { "The world is your oyster...\n" };
for(unsigned int i=0; i<8 * 64; i++){
if(testar_index==sizeof(testar)){testar_index=0;}
ram_tiles[i]=testar[testar_index];
testar_index++;
}
for(u8 t=0; t<1; t++){ SD_WriteSector(sectorStart, &ram_tiles); }
