OSDev.org

Stevo14 wrote:Does anyone know if it is possible to get either Qemu or Bochs to emulate a hard drive that only supports CHS? I was testing my OS on an old (ancient) computer and realized that its hard drive didn't support LBA (or at least that is what it told me from the identify command). My kernel only supports LBA right now so I though this would be a good opportunity to add support for legacy CHS addressing. Now what I need is a proper way (hopefully in an emulator) to test the CHS -> LBA and LBA -> CHS conversion code.

Brendan wrote:Hi,

Stevo14 wrote:Does anyone know if it is possible to get either Qemu or Bochs to emulate a hard drive that only supports CHS? I was testing my OS on an old (ancient) computer and realized that its hard drive didn't support LBA (or at least that is what it told me from the identify command). My kernel only supports LBA right now so I though this would be a good opportunity to add support for legacy CHS addressing. Now what I need is a proper way (hopefully in an emulator) to test the CHS -> LBA and LBA -> CHS conversion code.

Could you simply modify your code that detects if the hard drive supports LBA, so that the rest of the OS thinks the hard drive doesn't support LBA when it actually does?

Stevo14 wrote:

Brendan wrote:Could you simply modify your code that detects if the hard drive supports LBA, so that the rest of the OS thinks the hard drive doesn't support LBA when it actually does?

I've done something similar to that already. All reads and writes are addressed in LBA but if the drive doesn't support LBA, the address is converted to CHS on the fly before being sent to the drive. The code is already written, but now I need a way to test it and debug it without constantly transferring the kernel and rebooting.

Brendan wrote: (or if you modify the code to pretend that LBA isn't supported)

int ata_seek(ata_drive_t *d, unsigned int block)
{
	//null pointer
	if(d == 0)
		return -1;

	d->current_block = block;

	if(d->mode == ATA_LBA )
	{//lba addressing
		outportb(d->ports.LBA_low, d->current_block);
  		outportb(d->ports.LBA_mid,  d->current_block >> 8);
   	outportb(d->ports.LBA_high,  d->current_block >> 16);
   	outportb(d->ports.drive_head, d->id | ((d->current_block >> 24) & 0x0F));
	}
	else
	{//CHS addressing

		unsigned int cyl = d->current_block / (d->heads * d->sectors);
		unsigned int tmp = d->current_block % (d->heads * d->sectors);
		unsigned int head = tmp / d->sectors;
		unsigned int sect = tmp % d->sectors + 1;
	
		outportb(d->ports.LBA_low, sect);
  		outportb(d->ports.LBA_mid, cyl);
   	outportb(d->ports.LBA_high, cyl >> 8);
   	outportb(d->ports.drive_head, d->id | head);
	}
	
	return 0;
}

bewing wrote:but make sure that you note that timing issues are MUCH more vital on real hardware when you are dealing with a CHS-only drive.