NCR 53C80/53C400 driver

BACKGROUND
----------
The NCR 53C80 SCSI Bus Controller (SBC) is an early single-chip solution
which formed the basis of many early SCSI host adapters for both the
i386 and m68k platforms. The NCR 53C400 is a slightly more advanced
chip which retains backward compatability with the 53C80.

On the PC, the NCR 53C80 was most commonly used to implement simple, cheap
SCSI host adapters that were bundled with tape and CD-ROM drives. Since
these controllers were not bus-mastering (and in some cases were not even
interrupt-driven), they (like IDE adapters) required the CPU to perform
much of the actual processing. These days, these controllers are cheap
and plentiful since many are not supported by Windows 95.

Similarly, NetBSD, although it has had an MI 53C80 driver (used by the
Sun3 and Mac68k ports) for some time, has not had a i386 driver.

Until now, that is...

OVERVIEW
--------
The NCR 53C80/53C400 driver (the 'nca' device) consists of two pieces:

	1) Patches for the 53C80 MI driver to make it use bus_space()
	   functions. (This requires an optional define. By default,
	   the driver will compile in "legacy" memory-mapped mode.

	2) A machine-dependent driver (nca) containing probe and
	   attachment routines.

This driver has bene tested with the following adapters:

	NCS-250 (Chinon)	53C80, port-mapped, polled-mode
				(This is used in my primary development
				box to drive an external Zip drive.)
	Sumo SCSI-AT		53C80, port-mapped, interrupt driven
				(Note: This is an odd card in that its
				own firmware seems to have trouble detecting
				attached drives. Under NetBSD, however,
				it operates with no problems.)
	Trantor T-160		53C400, port-mapped, interrupt driven
				This card was often bundled with NEC
				CD-ROM drives. (My standalone test box
				is using this as its primary adapter.)
	DTC 3150V		53C400, memory-mapped, interrupt driven
				This a simple card designed to drive
				a CD-ROM.

CONFIGURATION
-------------
To setup the nca driver, the configuration file must contain the following:

	options	NCR5380_USE_BUS_SPACE

This line is required to add bus_space() compatability to the MI driver.

Next you need to add one or more configuration lines for the nca devices:

	nca0	at isa? port 0x360 irq 15
	nca1	at isa? iomem 0xd8000 irq 5

The first is for a port-mapped controller at 0x360, IRQ 15. The second line
is for a memory-mapped controller (Trantor T128 or equivalent) at
0xd800-0xdff, IRQ 5.

You can also set up the driver in "polled" mode (i.e., no interrupts) by
leaving off the "irq" portion of the line:

	nca0	at isa? port 0x360
	nca1	at isa? iomem 0xd8000

Lastly, you need to add a scsibus attachment line for the nca device:

	scsibus* at nca?

The following is the probe output from my test system:

	Copyright (c) 1996, 1997, 1998
	    The NetBSD Foundation, Inc.  All rights reserved.
	Copyright (c) 1982, 1986, 1989, 1991, 1993
	    The Regents of the University of California.  All rights reserved.
	
	NetBSD 1.3.2 (GENERIC) #2: Sun Oct  4 17:11:43 EDT 1998
	    root@hefalump:/usr/src/sys/arch/i386/compile/GENERIC
	cpu0: Intel 486DX (486-class)
	real mem  = 7995392
	avail mem = 5349376
	using 123 buffers containing 503808 bytes of memory
	mainbus0 (root)
	isa0 at mainbus0
	com1 at isa0 port 0x2f8-0x2ff irq 3: ns8250 or ns16450, no fifo
	com2 at isa0 port 0x3e8-0x3ef irq 5: ns8250 or ns16450, no fifo
	lpt0 at isa0 port 0x378-0x37b irq 7
	nca0 at isa0 port 0x360-0x36f irq 15
	nca0: NCR 53C400 detected
	scsibus0 at nca0: 8 targets
	sd0 at scsibus0 targ 0 lun 0: <HP, C2235, 0B11> SCSI2 0/direct fixed
	sd0: 402MB, 1574 cyl, 9 head, 58 sec, 512 bytes/sect x 825012 sectors
	cd0 at scsibus0 targ 6 lun 0: <CHINON, CD-ROM CDS-535, Q20> SCSI2 5/cdrom removable
	nca1 at isa0 iomem 0xdb878-0xdb887 irq 5
	nca1: NCR 53C400 detected
	scsibus1 at nca1: 8 targets
	sd1 at scsibus1 targ 5 lun 0: <IOMEGA, ZIP 100, J.02> SCSI2 0/direct removable
	sd1: 96MB, 96 cyl, 64 head, 32 sec, 512 bytes/sect x 196608 sectors
	npx0 at isa0 port 0xf0-0xff: using exception 16
	pc0 at isa0 port 0x60-0x6f irq 1: color
	pc0: console
	fdc0 at isa0 port 0x3f0-0x3f7 irq 6 drq 2
	fd0 at fdc0 drive 0: 1.44MB, 80 cyl, 2 head, 18 sec
	biomask 8060 netmask 8460 ttymask 84e2
	boot device: sd0
	root on sd0a dumps on sd0b
	root file system type: ffs

In this output, nca0 is a Trantor T-160 and nca1 is a DTC 3150V. Both happen
to be 53C400-based controllers.

LIMITATIONS
-----------
As of this writing, the nca driver has two known limitations:

1) No DMA or pseudo-DMA support

This is unfortunate, but may be remedied in a later release. I would welcome
any help by someone more familiar with DMA, particularly in relation to 
bus_space().

As it is, however, performance of the nca driver is acceptable, though some
of that may depend on one's definition of "acceptable". Remember that these
were not high speed controller under the best conditions, so much of it is
really the nature of the beast. It should be adequate for tapes, CD-ROMS, 
and low-usage disk devices (e.g., Zip drives). If you want to drive a CD-R
drive, then invest in an Adaptec 154X or a PCI controller.

2) No support for the SCSI port of the Pro AudioStudio 16.

This is also unfortunate and may not be able to be remedied withing the
current framework of the bus_space() functions and the nca driver.

The problem is this: In most adapters, the eight 53C80 registers are mapped
to eight sequential locations, either ports or memory addresses. On the
PAS-16, however, the registers are mapped to two sets of ports- four
sequential ports at the base address and four sequential ports located
0x2000 higher. As I currently understand it, this is not supportable by
the current bus_space() implementation nor is it possible for the driver
to allocate a second bus_space_tag and _handle itself to accomodate the
second set of ports. Without either, it is very difficult to imagine how
a portable linkage to the MI driver could be made.

Again, I welcome suggestions.

HISTORY
-------
An nca driver first appeared in FreeBSD.

This particular one borrows a little code from it and some from the i386
'esp' and sun3 'si' drivers. It, like many things in the free unix world,
was written because it solved a problem- mine! In my case, it was a need
of a SCSI card and a lack of IRQs. The good news was that I had one
(NCS-250); the bad news was that it was not supported under NetBSD. The
rest is history.

DISCLAIMER
----------
Like most things, you should take this code with a grain of salt. I have
tried to test it sufficiently, but it is always possible that it is not
compatible with some aspect of your system. If you end up suffering
massive data loss and destruction, you have my sympathies, but I do not
and will not allow myself to be held responsible.

CREDITS
-------
My thanks to Jason Thorpe and the rest of the NetBSD team for making it
so easy to write this driver. My thanks also to the authors of the
FreeBSD nca driver for inspiration and 53C400 support.

In the end, I hope that someone else can find this driver as useful as I
have. If so, please drop me a line at jruschme@exit109.com and let me 
know about it.

Share and enjoy

John Ruschmeyer (jruschme@exit109.com)
11 October 1998
