linux/Documentation/scsi/aha152x.txt
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   1$Id: README.aha152x,v 1.2 1999/12/25 15:32:30 fischer Exp fischer $
   2Adaptec AHA-1520/1522 SCSI driver for Linux (aha152x)
   3
   4Copyright 1993-1999 J├╝rgen Fischer <fischer@norbit.de>
   5TC1550 patches by Luuk van Dijk (ldz@xs4all.nl)
   6
   7
   8In Revision 2 the driver was modified a lot (especially the
   9bottom-half handler complete()).
  10
  11The driver is much cleaner now, has support for the new
  12error handling code in 2.3, produced less cpu load (much
  13less polling loops), has slightly higher throughput (at
  14least on my ancient test box; a i486/33Mhz/20MB).
  15
  16
  17CONFIGURATION ARGUMENTS:
  18
  19IOPORT        base io address                           (0x340/0x140)
  20IRQ           interrupt level                           (9-12; default 11)
  21SCSI_ID       scsi id of controller                     (0-7; default 7)
  22RECONNECT     allow targets to disconnect from the bus  (0/1; default 1 [on])
  23PARITY        enable parity checking                    (0/1; default 1 [on])
  24SYNCHRONOUS   enable synchronous transfers              (0/1; default 1 [on])
  25DELAY:        bus reset delay                           (default 100)
  26EXT_TRANS:    enable extended translation               (0/1: default 0 [off])
  27              (see NOTES)
  28
  29COMPILE TIME CONFIGURATION (go into AHA152X in drivers/scsi/Makefile):
  30
  31-DAUTOCONF
  32 use configuration the controller reports (AHA-152x only)
  33
  34-DSKIP_BIOSTEST
  35 Don't test for BIOS signature (AHA-1510 or disabled BIOS)
  36
  37-DSETUP0="{ IOPORT, IRQ, SCSI_ID, RECONNECT, PARITY, SYNCHRONOUS, DELAY, EXT_TRANS }"
  38 override for the first controller 
  39
  40-DSETUP1="{ IOPORT, IRQ, SCSI_ID, RECONNECT, PARITY, SYNCHRONOUS, DELAY, EXT_TRANS }"
  41 override for the second controller
  42
  43-DAHA152X_DEBUG
  44 enable debugging output
  45
  46-DAHA152X_STAT
  47 enable some statistics
  48
  49
  50LILO COMMAND LINE OPTIONS:
  51
  52aha152x=<IOPORT>[,<IRQ>[,<SCSI-ID>[,<RECONNECT>[,<PARITY>[,<SYNCHRONOUS>[,<DELAY> [,<EXT_TRANS]]]]]]]
  53
  54 The normal configuration can be overridden by specifying a command line.
  55 When you do this, the BIOS test is skipped. Entered values have to be
  56 valid (known).  Don't use values that aren't supported under normal
  57 operation.  If you think that you need other values: contact me.
  58 For two controllers use the aha152x statement twice.
  59
  60
  61SYMBOLS FOR MODULE CONFIGURATION:
  62
  63Choose from 2 alternatives:
  64
  651. specify everything (old)
  66
  67aha152x=IOPORT,IRQ,SCSI_ID,RECONNECT,PARITY,SYNCHRONOUS,DELAY,EXT_TRANS
  68  configuration override for first controller
  69
  70
  71aha152x1=IOPORT,IRQ,SCSI_ID,RECONNECT,PARITY,SYNCHRONOUS,DELAY,EXT_TRANS
  72  configuration override for second controller
  73
  742. specify only what you need to (irq or io is required; new)
  75
  76io=IOPORT0[,IOPORT1]
  77  IOPORT for first and second controller
  78
  79irq=IRQ0[,IRQ1]
  80  IRQ for first and second controller
  81
  82scsiid=SCSIID0[,SCSIID1]
  83  SCSIID for first and second controller
  84
  85reconnect=RECONNECT0[,RECONNECT1]
  86  allow targets to disconnect for first and second controller
  87
  88parity=PAR0[PAR1]
  89  use parity for first and second controller
  90
  91sync=SYNCHRONOUS0[,SYNCHRONOUS1]
  92  enable synchronous transfers for first and second controller
  93
  94delay=DELAY0[,DELAY1]
  95  reset DELAY for first and second controller
  96
  97exttrans=EXTTRANS0[,EXTTRANS1]
  98  enable extended translation for first and second controller
  99
 100
 101If you use both alternatives the first will be taken.
 102
 103
 104NOTES ON EXT_TRANS: 
 105
 106SCSI uses block numbers to address blocks/sectors on a device.
 107The BIOS uses a cylinder/head/sector addressing scheme (C/H/S)
 108scheme instead.  DOS expects a BIOS or driver that understands this
 109C/H/S addressing.
 110
 111The number of cylinders/heads/sectors is called geometry and is required
 112as base for requests in C/H/S addressing.  SCSI only knows about the
 113total capacity of disks in blocks (sectors).
 114
 115Therefore the SCSI BIOS/DOS driver has to calculate a logical/virtual
 116geometry just to be able to support that addressing scheme.  The geometry
 117returned by the SCSI BIOS is a pure calculation and has nothing to
 118do with the real/physical geometry of the disk (which is usually
 119irrelevant anyway).
 120
 121Basically this has no impact at all on Linux, because it also uses block
 122instead of C/H/S addressing.  Unfortunately C/H/S addressing is also used
 123in the partition table and therefore every operating system has to know
 124the right geometry to be able to interpret it.
 125
 126Moreover there are certain limitations to the C/H/S addressing scheme,
 127namely the address space is limited to up to 255 heads, up to 63 sectors
 128and a maximum of 1023 cylinders.
 129
 130The AHA-1522 BIOS calculates the geometry by fixing the number of heads
 131to 64, the number of sectors to 32 and by calculating the number of
 132cylinders by dividing the capacity reported by the disk by 64*32 (1 MB).
 133This is considered to be the default translation.
 134
 135With respect to the limit of 1023 cylinders using C/H/S you can only
 136address the first GB of your disk in the partition table.  Therefore
 137BIOSes of some newer controllers based on the AIC-6260/6360 support
 138extended translation.  This means that the BIOS uses 255 for heads,
 13963 for sectors and then divides the capacity of the disk by 255*63
 140(about 8 MB), as soon it sees a disk greater than 1 GB.  That results
 141in a maximum of about 8 GB addressable diskspace in the partition table
 142(but there are already bigger disks out there today).
 143
 144To make it even more complicated the translation mode might/might
 145not be configurable in certain BIOS setups.
 146
 147This driver does some more or less failsafe guessing to get the
 148geometry right in most cases:
 149
 150- for disks<1GB: use default translation (C/32/64)
 151
 152- for disks>1GB:
 153  - take current geometry from the partition table
 154    (using scsicam_bios_param and accept only `valid' geometries,
 155    ie. either (C/32/64) or (C/63/255)).  This can be extended translation
 156    even if it's not enabled in the driver.
 157
 158  - if that fails, take extended translation if enabled by override,
 159    kernel or module parameter, otherwise take default translation and
 160    ask the user for verification.  This might on not yet partitioned
 161    disks.
 162
 163
 164REFERENCES USED:
 165
 166 "AIC-6260 SCSI Chip Specification", Adaptec Corporation.
 167
 168 "SCSI COMPUTER SYSTEM INTERFACE - 2 (SCSI-2)", X3T9.2/86-109 rev. 10h
 169
 170 "Writing a SCSI device driver for Linux", Rik Faith (faith@cs.unc.edu)
 171
 172 "Kernel Hacker's Guide", Michael K. Johnson (johnsonm@sunsite.unc.edu)
 173
 174 "Adaptec 1520/1522 User's Guide", Adaptec Corporation.
 175
 176 Michael K. Johnson (johnsonm@sunsite.unc.edu)
 177
 178 Drew Eckhardt (drew@cs.colorado.edu)
 179
 180 Eric Youngdale (eric@andante.org) 
 181
 182 special thanks to Eric Youngdale for the free(!) supplying the
 183 documentation on the chip.
 184
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