Floppy Disk Controller does not want to write to sector 3

[JSmith2]

Hello, I am fairly new to operating system development. I have been lately trying to create a floppy disk controller driver that can read and write to and from a floppy. I have made the fdc to read and write, but when I tested it to write one sector (512bytes) the the third sector, my hex editor shows no change. I did the same test writing to the fourth sector, first sector, fifth sector, twentieth sector, everything worked. Writing to the third sector is the issue. I also did a test where I wrote 2 sectors (1 KB) starting at the third sector, and everything worked fine. Has anyone expirienced such problems with their fdc driver.

Here is the write sector code (the data I want to write is in the DMA already):

Code: Select all

//the floppy must be on in order to read from it
    floppy_motor(FLOPPY_MOTOR_ON, _CurrentDrive);
  
    //set the dma to write
    set_floppy_dma(FALSE);
  
    //send command that we want to write to a sector with some generic flags
    floppy_send_command(FDC_CMD_WRITE_SECT | FDC_CMD_EXT_MULTITRACK |
                        FDC_CMD_EXT_SKIP | FDC_CMD_EXT_DENSITY);
  
    //specify which head and drive to use
    floppy_send_command((head << 2) | _CurrentDrive);
    floppy_send_command(track);    //specify the track
    floppy_send_command(head);     //specify the head
    floppy_send_command(sector);   //specify the sector
    floppy_send_command(FLOPPY_SECTOR_DTL_512); //specify to use 512 bytes per sector
  
    k_printf("head: %d, track: %d, sector: %d, size %d\n", head, track, sector, (s32int)((size - 1) / SECTOR_SIZE) + 1);
  
    /*send command to write the ceil of the number of sectors that make
     * up size, (size - 1) / SECTOR_SIZE, add 1 to make it ceiling
     *
     * the -1 in (size - 1) is used if size == SECTOR_SIZE, then the output
     * of this calculation would be still 1 sector, without the -1, the ouput
     * would be 2 which is incorrect*/
    floppy_send_command((s32int)((size - 1) / SECTOR_SIZE) + 1);
  
    //state that we are using a 3.5in floppy disk
    floppy_send_command(FLOPPY_GAP3_LENGTH_3_5);
    floppy_send_command(0xff); //floppy data length, set to 0xff if sector size != 0
  
    //wait for interupt
    floppy_wait_irq();
  
    //read the status info
    u32int _st0, _st1, _st2, ncyl, ehead, esect, final;
    _st0 = floppy_read_data();
    _st1 = floppy_read_data();
    _st2 = floppy_read_data();
    ncyl = floppy_read_data();
    ehead = floppy_read_data();
    esect = floppy_read_data();
    final = floppy_read_data();
  
    //let the FDC aknowledge that the interupt has been handled
    floppy_check_int(&st0, &cyl);

    if(!(_st0 & 0xc0))
    {
      break;

    }

My first assumption for the solution to this issue was the floppy disk read/write protection, although I also cannot successfully read from the third sector with a sector size of 1. I can read successfully with a sector size of > 1 sector though. Could this be the issue?
Thank you.

[JSmith2]

Well, I found out the problem and it had nothing to do with read/write protections.

I had a COMPLETE, RTFM moment. RAGE!!!

I followed the brokenthorn tutorial on the floppy disk controller driver as I was making it, and that tutorial only had a read sector function. I had to create my own write sector function, and I used the osDevWiki page on the floppy disk controller to make it, to an extent.

What the real issue was the format of the commands were different. The format of read is 'M F S 0 0 1 1 0' and the format for write is 'M F 0 0 0 1 1 0'. I did not notice the missing 'S' and was sending the read format flags when trying to write. I removed that extraneous 'S' and it works like a charm!

If you did not understand this, the brokenthorn tutorial has a detailed explanation. It is under the sections "Write Sector" and "Read Sector".

I hope this will aid anyone having a similar problem.