CompuServe Messages

Writing a SCSI device driver requires a lot of information about the SCSI controller (the chip's instruction set, memory and DMA use, etc.). A lot of that info is hard to get from board mfgs. If you're making your own SCSI controller, then you also have to deal with Zorro bus details. It's a *lot* of work. If you're just wanting to write a handler for a specific type of SCSI device that attaches to any ole SCSI board in your Amiga, things get a whole lot easier. Your handler can just make SCSIDirect calls to the SCSI device driver (assuming that the driver supports SCSIDirect…most do). This allows you to send any SCSI commands that you need to without having to worry about the details of the SCSI protocol (nice!). A "handler" is just another type of device driver, usually the next layer of abstraction up from ".devices" on the Amiga. There's a number of handlers that include source code around, and they're a help. SCSI command specs (or SCSI-II if you need 'em) are floating around a number of places. I got the full SCSI-II document from the NCR SCSI BBS. It's very detailed. I've been using a 2000 for bench testing some SCSI devices that are downright weird. It's very, very easy to hack in SCSI with an Amiga and a A2091 or GVP SII board. I tried to use a clone with an AH-1540 but gave up because of memory problems and SCSI command programming contortions that are required in the MS-DOS world (try READing 2MB of data in one command!). Only on the Amiga could I do this "on the cheap"…