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+$Id: README.aha152x,v 1.2 1999/12/25 15:32:30 fischer Exp fischer $
+Adaptec AHA-1520/1522 SCSI driver for Linux (aha152x)
+
+Copyright 1993-1999 Jürgen Fischer <fischer@norbit.de>
+TC1550 patches by Luuk van Dijk (ldz@xs4all.nl)
+
+
+In Revision 2 the driver was modified a lot (especially the
+bottom-half handler complete()).
+
+The driver is much cleaner now, has support for the new
+error handling code in 2.3, produced less cpu load (much
+less polling loops), has slightly higher throughput (at
+least on my ancient test box; a i486/33Mhz/20MB).
+
+
+CONFIGURATION ARGUMENTS:
+
+IOPORT        base io address                           (0x340/0x140)
+IRQ           interrupt level                           (9-12; default 11)
+SCSI_ID       scsi id of controller                     (0-7; default 7)
+RECONNECT     allow targets to disconnect from the bus  (0/1; default 1 [on])
+PARITY        enable parity checking                    (0/1; default 1 [on])
+SYNCHRONOUS   enable synchronous transfers              (0/1; default 1 [on])
+DELAY:        bus reset delay                           (default 100)
+EXT_TRANS:    enable extended translation               (0/1: default 0 [off])
+              (see NOTES)
+
+COMPILE TIME CONFIGURATION (go into AHA152X in drivers/scsi/Makefile):
+
+-DAUTOCONF
+ use configuration the controller reports (AHA-152x only)
+
+-DSKIP_BIOSTEST
+ Don't test for BIOS signature (AHA-1510 or disabled BIOS)
+
+-DSETUP0="{ IOPORT, IRQ, SCSI_ID, RECONNECT, PARITY, SYNCHRONOUS, DELAY, EXT_TRANS }"
+ override for the first controller 
+
+-DSETUP1="{ IOPORT, IRQ, SCSI_ID, RECONNECT, PARITY, SYNCHRONOUS, DELAY, EXT_TRANS }"
+ override for the second controller
+
+-DAHA152X_DEBUG
+ enable debugging output
+
+-DAHA152X_STAT
+ enable some statistics
+
+
+LILO COMMAND LINE OPTIONS:
+
+aha152x=<IOPORT>[,<IRQ>[,<SCSI-ID>[,<RECONNECT>[,<PARITY>[,<SYNCHRONOUS>[,<DELAY> [,<EXT_TRANS]]]]]]]
+
+ The normal configuration can be overridden by specifying a command line.
+ When you do this, the BIOS test is skipped. Entered values have to be
+ valid (known).  Don't use values that aren't supported under normal
+ operation.  If you think that you need other values: contact me.
+ For two controllers use the aha152x statement twice.
+
+
+SYMBOLS FOR MODULE CONFIGURATION:
+
+Choose from 2 alternatives:
+
+1. specify everything (old)
+
+aha152x=IOPORT,IRQ,SCSI_ID,RECONNECT,PARITY,SYNCHRONOUS,DELAY,EXT_TRANS
+  configuration override for first controller
+
+
+aha152x1=IOPORT,IRQ,SCSI_ID,RECONNECT,PARITY,SYNCHRONOUS,DELAY,EXT_TRANS
+  configuration override for second controller
+
+2. specify only what you need to (irq or io is required; new)
+
+io=IOPORT0[,IOPORT1]
+  IOPORT for first and second controller
+
+irq=IRQ0[,IRQ1]
+  IRQ for first and second controller
+
+scsiid=SCSIID0[,SCSIID1]
+  SCSIID for first and second controller
+
+reconnect=RECONNECT0[,RECONNECT1]
+  allow targets to disconnect for first and second controller
+
+parity=PAR0[PAR1]
+  use parity for first and second controller
+
+sync=SYNCHRONOUS0[,SYNCHRONOUS1]
+  enable synchronous transfers for first and second controller
+
+delay=DELAY0[,DELAY1]
+  reset DELAY for first and second controller
+
+exttrans=EXTTRANS0[,EXTTRANS1]
+  enable extended translation for first and second controller
+
+
+If you use both alternatives the first will be taken.
+
+
+NOTES ON EXT_TRANS: 
+
+SCSI uses block numbers to address blocks/sectors on a device.
+The BIOS uses a cylinder/head/sector addressing scheme (C/H/S)
+scheme instead.  DOS expects a BIOS or driver that understands this
+C/H/S addressing.
+
+The number of cylinders/heads/sectors is called geometry and is required
+as base for requests in C/H/S addressing.  SCSI only knows about the
+total capacity of disks in blocks (sectors).
+
+Therefore the SCSI BIOS/DOS driver has to calculate a logical/virtual
+geometry just to be able to support that addressing scheme.  The geometry
+returned by the SCSI BIOS is a pure calculation and has nothing to
+do with the real/physical geometry of the disk (which is usually
+irrelevant anyway).
+
+Basically this has no impact at all on Linux, because it also uses block
+instead of C/H/S addressing.  Unfortunately C/H/S addressing is also used
+in the partition table and therefore every operating system has to know
+the right geometry to be able to interpret it.
+
+Moreover there are certain limitations to the C/H/S addressing scheme,
+namely the address space is limited to up to 255 heads, up to 63 sectors
+and a maximum of 1023 cylinders.
+
+The AHA-1522 BIOS calculates the geometry by fixing the number of heads
+to 64, the number of sectors to 32 and by calculating the number of
+cylinders by dividing the capacity reported by the disk by 64*32 (1 MB).
+This is considered to be the default translation.
+
+With respect to the limit of 1023 cylinders using C/H/S you can only
+address the first GB of your disk in the partition table.  Therefore
+BIOSes of some newer controllers based on the AIC-6260/6360 support
+extended translation.  This means that the BIOS uses 255 for heads,
+63 for sectors and then divides the capacity of the disk by 255*63
+(about 8 MB), as soon it sees a disk greater than 1 GB.  That results
+in a maximum of about 8 GB addressable diskspace in the partition table
+(but there are already bigger disks out there today).
+
+To make it even more complicated the translation mode might/might
+not be configurable in certain BIOS setups.
+
+This driver does some more or less failsafe guessing to get the
+geometry right in most cases:
+
+- for disks<1GB: use default translation (C/32/64)
+
+- for disks>1GB:
+  - take current geometry from the partition table
+    (using scsicam_bios_param and accept only `valid' geometries,
+    ie. either (C/32/64) or (C/63/255)).  This can be extended translation
+    even if it's not enabled in the driver.
+
+  - if that fails, take extended translation if enabled by override,
+    kernel or module parameter, otherwise take default translation and
+    ask the user for verification.  This might on not yet partitioned
+    disks.
+
+
+REFERENCES USED:
+
+ "AIC-6260 SCSI Chip Specification", Adaptec Corporation.
+
+ "SCSI COMPUTER SYSTEM INTERFACE - 2 (SCSI-2)", X3T9.2/86-109 rev. 10h
+
+ "Writing a SCSI device driver for Linux", Rik Faith (faith@cs.unc.edu)
+
+ "Kernel Hacker's Guide", Michael K. Johnson (johnsonm@sunsite.unc.edu)
+
+ "Adaptec 1520/1522 User's Guide", Adaptec Corporation.
+
+ Michael K. Johnson (johnsonm@sunsite.unc.edu)
+
+ Drew Eckhardt (drew@cs.colorado.edu)
+
+ Eric Youngdale (eric@andante.org) 
+
+ special thanks to Eric Youngdale for the free(!) supplying the
+ documentation on the chip.