Read from disk - myOS

[Rocobo]

this is my disk driver code:

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// function read data from disk info buffer and return if succeed
void read28(unsigned int lba, char* buffer, unsigned sector_count)
{
	unsigned int offset = 0;
	unsigned int i = 0;

	// prepare the hard disk controller for reading (by specefic protocol - taken from ATA PIO Mode osDev)
	out_byte(ATA_ERR_INFO_PORT, 0x00);
	out_byte(ATA_SECTOR_COUNT_REGISTER_PORT, (unsigned char)sector_count);		// sector count
	out_byte(ATA_LBA_LOW_REGISTER_PORT, (unsigned char)lba); 					// Send the low 8 bits of the LBA
	out_byte(ATA_LBA_MID_REGISTER_PORT, (unsigned char)(lba>>8));				// Send the mid 8 bits of the LBA
	out_byte(ATA_LBA_HIGH_REGISTER_PORT, (unsigned char)(lba>>16)); 			// Send the high 8 bits of the LBA
	out_byte(ATA_DRIVE_REGISTER_PORT, 0xE0 | 0x40 | ((lba>>24) & 0x0F)); 		// master drive + lba + high lba bits
	out_byte(ATA_COMMAND_REGISTER_PORT, ATA_READ); 								// read command
	
	// for every sector - read into buffer
	while(sector_count--) {
		ata_wait_for_rdy(ATA_REGULAR_STATUS_REGISTER_PORT); // Spun up
        ata_wait_for_drq(ATA_REGULAR_STATUS_REGISTER_PORT); // Ready for transfer
		for(i = 0;i < 256;i++) 
		{
			// write data from disk into buffer
			*( (unsigned short *)buffer + offset + i ) = in_word(ATA_DATA_REGISTER_PORT);
		}
		offset += 256;
	}
}

During my OS execution there is sometimes when my OS freeze becouse of reading some sector from disk...
How can i fix this probelm ? I use this function in my FS FAT32

[Klakap]

Did you acknowledge interrupt with reading from status port(offset 7)? In emulators Primary IDE have irq14 and secondary IDE have irq15.

[BenLunt]

Hi,

As Klakap stated, you need to acknowledge the interrupt by reading from the STATUS register after the read.

Most likely, you are reading from this status register every loop iteration at

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  ata_wait_for_rdy(ATA_REGULAR_STATUS_REGISTER_PORT); // Spun up
  ata_wait_for_drq(ATA_REGULAR_STATUS_REGISTER_PORT); // Ready for transfer

but after the last sector read, you do not read from it.

The ata_wait_for_rdy (and _drq) should be reading from the ALT Status register, and then you should read from the Status register after the for() loop, checking for errors.

On a side note, the:

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ata_wait_for_rdy(ATA_REGULAR_STATUS_REGISTER_PORT); // Spun up

is not required since your drive should already be spinning. A CD-ROM is most likely an ATAPI device and you can't read from it using this form of read command.

Ben
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