2 Introduction.

The Atari has always lacked system-global SCSI routines. Thus everyone who wants to programme SCSI devices has to write their own routines, and has to start afresh each time a new computer appears.

Furthermore it is sensible to make true SCSI ports (as in a TT, Falcon or the Medusa) also appear as targets.

To this must be added alternative SCSI ports that can be fitted on accessory cards to the ST, TT or the Medusa.

Emulators (e.g. MagiCMac, STonX) or alternative computers (clones) are of special importance, since it is not possible to access their SCSI ports if one doesn't know the hardware.

Hence this scheme for the installation of a global SCSI handler. Potentially the handler can already be installed in the operating system, thus allowing the hard disk drivers to access the alternative SCSI ports as well without requiring information about the hardware implementation.

From this arises the following procedure for all SCSI-using programs:

• If the SCSI cookie exists then the functions made available by it should be used.
   
• If the cookie does not exist then a program's own routines, if present, should be used.
   
  Programs that rely only on the routines used here and have no own routines on board must abort with a corresponding error message in that case.
   

Hard disk drivers should also do this, since there could be reset-proof or RAM-resident SCSI drivers that are meant to be used by the hard disk driver.

If the cookie is not installed then it is sensible for hard disk drivers to install one, to make their own routines available globally.

Desired features of the SCSI driver:

• Capability for transferring any length of data on ACSI (remember the DMA fifo hole of the DMA-chip).
   
• Class 1 commands on ACSI (per ALIA, Linked-Cmd or ICD method).
   
• FRB-transfers (ACSI) are a task of the driver.