Why i can only read 2 times by my floppy driver?

[iamxiaohan]

hi,i encounter a very strange problem. i write a floppy driver, but i only use it 2 times. if i want read any more, it can't work. i don't know why. can you help me? thank you!
the following is my some code.
============================
void floppy_read( unsigned char sector , unsigned char cylinder , unsigned char head )
{
floppy_reset() ;

floppy_seek_cylinder( head , cylinder ) ;

dma_open_dma_channel( 2 , floppy_buffer_address , 512 , DMA_READ_MODEL ) ;

floppy_send_byte_return_is_ok( 0x66 ) ;
floppy_send_byte_return_is_ok( head << 2 ) ;
floppy_send_byte_return_is_ok( cylinder ) ;
floppy_send_byte_return_is_ok( head ) ;
floppy_send_byte_return_is_ok( sector ) ;
floppy_send_byte_return_is_ok( 2 ) ;
floppy_send_byte_return_is_ok( 18 ) ;
floppy_send_byte_return_is_ok( 27 ) ;
floppy_send_byte_return_is_ok( 255 ) ;

floppy_wait_for_interrupt() ;
}

void floppy_reset()
{
io_write_to_io_port( 0x3f2 , 0 ) ;
io_write_to_io_port( 0x3f2 , 0x1c ) ;
floppy_wait_for_interrupt() ;
for( int i = 0 ; i < 4 ; ++i ){
floppy_read_status() ;
}
floppy_set_specification() ;
floppy_recalibrate() ;
}

void kernel_main()
{
.....
floppy_read( 1 , 0 , 0 ) ; // well
floppy_read( 2 , 0 , 0 ) ; // well
floppy_read( 3 , 0 , 0 ) ; // bad! this statement doesn't work, but why???
....
}

[iamxiaohan]

btw: i test it on bochs 2.11

[Brendan]

Hi,

btw: i test it on bochs 2.11

What do you get for the results of the read data command, most specifically, ST0, ST1 and ST2?

These results should be read when the IRQ is received - they contain flags that say if the command worked (and if it didn't why it didn't work).

BTW you shouldn't need to reset the floppy drive controller every time you read some data...


Cheers,

Brendan

[ASHLEY4]

Here are my thought, i have just made a floppy driver, but in asm, i do not use C, but what i can read between the lines your looks the same as mine, but for two things.
you send 0x66, i send 0xe6, also to me you must read 7 bytes after the interrupt, i do not know if it makes a differenc, but is does on the reset command, so maybe it needs it on the read sector ?

Or may be its boch giving you a hard time, have you tryed it in a real pc ?.

ps: i have not got my floppy code with me so above is from memory.

\\\\||////
(@@)
ASHLEY4.

[Brendan]

Hi,

you send 0x66, i send 0xe6, also to me you must read 7 bytes after the interrupt, i do not know if it makes a differenc, but is does on the reset command, so maybe it needs it on the read sector ?

The difference between 0x66 and 0xE6 is the MT (multi-track) bit, which shouldn't matter as only one track is being read.

There is a bug I didn't notice - commands are being sent to read sectors 1 to 18, then sectors 2 to 18, then sectors 3 to 18, but the DMA transfer is set up to only read a single sector. Because of this the read commands should all fail (Overrun/Underrun bit set in ST1) after transferring one sector. From this I assume that the status bytes are not read (or are read and ignored), and the first 2 reads are assumed to have worked because one sector is read.

Also there doesn't seem to be anything turning the floppy motor on (or off). This might be done within "floppy_recalibrate()" or something.

The 7 status bytes might also be read within "floppy_wait_for_interrupt()" or in the IRQ handler (although I can't see how either of these can know how many bytes to expect, unless it's hard-coded which would make things harder when other floppy commands are added).


Cheers,

Brendan