CDFS Driver

Document version 0.10, December 2002

Introduction

This document describes the new and updated CD API's in RISC OS 5.00.

Note that ATAPI devices, such as CD drives, are controlled using SCSI command packets sent from the host. The SCSI command packets are transported over the ATA interface instead of a SCSI bus. References to SCSI refer to the SCSI command packets and not a SCSI interface.

A useful guide to the ATAPI interface can be found at http://www.ata-atapi.com/index.htm

SWI CD_Register (SWI &41260) / CD_Unregister (SWI &41261)

Bit 21 of the information word may be set to indicate that CDFSDriver should call SWI SCSI_Op to implement SWI CD_SCSIUserOp, instead of calling the soft-loadable driver.

SWI CD_SCSIUserOp (SWI &4126B)

On entry:	R0 =	bits 24-25 = 0 => no data transfer
		= 1 => read
		= 2 => write
		= 3 reserved
	R1 =	length of control block
	R2 ->	control block
	R3 ->	buffer for data transfer
	R4 =	length of transfer
	R5 =	timeout in cs (0 = default)
	R7 ->	CDFS control block
On exit:	R3,R4	updated
	R5-R9	preserved
		NZC flags corrupted
		If V set,
		R0-R2 are as for SWI SCSI_Op
		or R0 -> error not in SCSI range and R1,R2 corrupt
		Else R0-R2 preserved

CD_SCSIUserOp must not be called in the background (for compatibility with ATAPI drives).

"Soft-loadable" drivers

Entry #36 ("SCSIUserOp")

On entry:	R0	bits 24-25:
		= 0 => no data transfer
		= 1 => read
		= 2 => write
		= 3 reserved
	R1 =	length of control block
	R2 ->	control block
	R3 ->	buffer for data transfer
	R4 =	length of transfer
	R5 =	timeout in cs (0 = default)
	R7 ->	CDFS control block
	R11 =	reason code (36)
	R12 =	workspace
On exit:	R3,R4	updated
	R5-R12	may be corrupted
	NZC flags	may be corrupted
	If V set:	R0-R2 are as for SWI SCSI_Op
		or R0 -> error not in SCSI range and R1,R2 may be corrupted
	If V clear:	R0-R2 may be corrupted