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phoenix |
i386 Micro Channel Architecture Support
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=======================================
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MCA support is enabled using the CONFIG_MCA define. A machine with a MCA
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bus will have the kernel variable MCA_bus set, assuming the BIOS feature
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bits are set properly (see arch/i386/boot/setup.S for information on
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how this detection is done).
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Adapter Detection
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=================
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The ideal MCA adapter detection is done through the use of the
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Programmable Option Select registers. Generic functions for doing
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this have been added in include/linux/mca.h and arch/i386/kernel/mca.c.
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Everything needed to detect adapters and read (and write) configuration
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information is there. A number of MCA-specific drivers already use
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this. The typical probe code looks like the following:
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#include
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unsigned char pos2, pos3, pos4, pos5;
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struct net_device* dev;
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int slot;
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if( MCA_bus ) {
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slot = mca_find_adapter( ADAPTER_ID, 0 );
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if( slot == MCA_NOTFOUND ) {
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return -ENODEV;
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}
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/* optional - see below */
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mca_set_adapter_name( slot, "adapter name & description" );
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mca_set_adapter_procfn( slot, dev_getinfo, dev );
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/* read the POS registers. Most devices only use 2 and 3 */
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pos2 = mca_read_stored_pos( slot, 2 );
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pos3 = mca_read_stored_pos( slot, 3 );
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pos4 = mca_read_stored_pos( slot, 4 );
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pos5 = mca_read_stored_pos( slot, 5 );
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} else {
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return -ENODEV;
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}
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/* extract configuration from pos[2345] and set everything up */
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Loadable modules should modify this to test that the specified IRQ and
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IO ports (plus whatever other stuff) match. See 3c523.c for example
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code (actually, smc-mca.c has a slightly more complex example that can
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handle a list of adapter ids).
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Keep in mind that devices should never directly access the POS registers
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(via inb(), outb(), etc). While it's generally safe, there is a small
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potential for blowing up hardware when it's done at the wrong time.
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Furthermore, accessing a POS register disables a device temporarily.
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This is usually okay during startup, but do _you_ want to rely on it?
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During initial configuration, mca_init() reads all the POS registers
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into memory. mca_read_stored_pos() accesses that data. mca_read_pos()
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and mca_write_pos() are also available for (safer) direct POS access,
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but their use is _highly_ discouraged. mca_write_pos() is particularly
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dangerous, as it is possible for adapters to be put in inconsistent
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states (i.e. sharing IO address, etc) and may result in crashes, toasted
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hardware, and blindness.
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User level drivers (such as the AGX X server) can use /proc/mca/pos to
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find adapters (see below).
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Some MCA adapters can also be detected via the usual ISA-style device
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probing (many SCSI adapters, for example). This sort of thing is highly
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discouraged. Perfectly good information is available telling you what's
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there, so there's no excuse for messing with random IO ports. However,
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we MCA people still appreciate any ISA-style driver that will work with
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our hardware. You take what you can get...
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Level-Triggered Interrupts
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==========================
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Because MCA uses level-triggered interrupts, a few problems arise with
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what might best be described as the ISA mindset and its effects on
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drivers. These sorts of problems are expected to become less common as
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more people use shared IRQs on PCI machines.
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In general, an interrupt must be acknowledged not only at the ICU (which
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is done automagically by the kernel), but at the device level. In
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particular, IRQ 0 must be reset after a timer interrupt (now done in
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arch/i386/kernel/time.c) or the first timer interrupt hangs the system.
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There were also problems with the 1.3.x floppy drivers, but that seems
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to have been fixed.
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IRQs are also shareable, and most MCA-specific devices should be coded
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with shared IRQs in mind.
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/proc/mca
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=========
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/proc/mca is a directory containing various files for adapters and
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other stuff.
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/proc/mca/pos Straight listing of POS registers
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/proc/mca/slot[1-8] Information on adapter in specific slot
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/proc/mca/video Same for integrated video
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/proc/mca/scsi Same for integrated SCSI
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/proc/mca/machine Machine information
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See Appendix A for a sample.
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Device drivers can easily add their own information function for
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specific slots (including integrated ones) via the
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mca_set_adapter_procfn() call. Drivers that support this are ESDI, IBM
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SCSI, and 3c523. If a device is also a module, make sure that the proc
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function is removed in the module cleanup. This will require storing
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the slot information in a private structure somewhere. See the 3c523
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driver for details.
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Your typical proc function will look something like this:
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static int
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dev_getinfo( char* buf, int slot, void* d ) {
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struct net_device* dev = (struct net_device*) d;
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int len = 0;
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len += sprintf( buf+len, "Device: %s\n", dev->name );
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len += sprintf( buf+len, "IRQ: %d\n", dev->irq );
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len += sprintf( buf+len, "IO Port: %#lx-%#lx\n", ... );
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...
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return len;
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}
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Some of the standard MCA information will already be printed, so don't
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bother repeating it. Don't try putting in more than 3K of information.
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Enable this function with:
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mca_set_adapter_procfn( slot, dev_getinfo, dev );
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Disable it with:
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mca_set_adapter_procfn( slot, NULL, NULL );
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It is also recommended that, even if you don't write a proc function, to
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set the name of the adapter (i.e. "PS/2 ESDI Controller") via
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mca_set_adapter_name( int slot, char* name ).
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MCA Device Drivers
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==================
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Currently, there are a number of MCA-specific device drivers.
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1) PS/2 ESDI
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drivers/block/ps2esdi.c
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include/linux/ps2esdi.h
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Uses major number 36, and should use /dev files /dev/eda, /dev/edb.
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Supports two drives, but only one controller. May use the
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command-line args "ed=cyl,head,sec" and "tp720".
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2) PS/2 SCSI
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drivers/scsi/ibmmca.c
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drivers/scsi/ibmmca.h
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The driver for the IBM SCSI subsystem. Includes both integrated
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controllers and adapter cards. May require command-line arg
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"ibmmcascsi=io_port" to force detection of an adapter. If you have a
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machine with a front-panel display (i.e. model 95), you can use
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"ibmmcascsi=display" to enable a drive activity indicator.
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3) 3c523
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drivers/net/3c523.c
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drivers/net/3c523.h
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3Com 3c523 Etherlink/MC ethernet driver.
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4) SMC Ultra/MCA and IBM Adapter/A
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drivers/net/smc-mca.c
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drivers/net/smc-mca.h
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Driver for the MCA version of the SMC Ultra and various other
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OEM'ed and work-alike cards (Elite, Adapter/A, etc).
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5) NE/2
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driver/net/ne2.c
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driver/net/ne2.h
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The NE/2 is the MCA version of the NE2000. This may not work
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with clones that have a different adapter id than the original
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NE/2.
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6) Future Domain MCS-600/700, OEM'd IBM Fast SCSI Aapter/A and
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Reply Sound Blaster/SCSI (SCSI part)
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Better support for these cards than the driver for ISA.
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Supports multiple cards with IRQ sharing.
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Also added boot time option of scsi-probe, which can do reordering of
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SCSI host adapters. This will direct the kernel on the order which
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SCSI adapter should be detected. Example:
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scsi-probe=ibmmca,fd_mcs,adaptec1542,buslogic
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The serial drivers were modified to support the extended IO port range
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of the typical MCA system (also #ifdef CONFIG_MCA).
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The following devices work with existing drivers:
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1) Token-ring
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2) Future Domain SCSI (MCS-600, MCS-700, not MCS-350, OEM'ed IBM SCSI)
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3) Adaptec 1640 SCSI (using the aha1542 driver)
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4) Bustek/Buslogic SCSI (various)
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5) Probably all Arcnet cards.
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6) Some, possibly all, MCA IDE controllers.
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7) 3Com 3c529 (MCA version of 3c509) (patched)
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8) Intel EtherExpressMC (patched version)
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You need to have CONFIG_MCA defined to have EtherExpressMC support.
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9) Reply Sound Blaster/SCSI (SB part) (patched version)
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Bugs & Other Weirdness
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======================
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NMIs tend to occur with MCA machines because of various hardware
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weirdness, bus timeouts, and many other non-critical things. Some basic
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code to handle them (inspired by the NetBSD MCA code) has been added to
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detect the guilty device, but it's pretty incomplete. If NMIs are a
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persistent problem (on some model 70 or 80s, they occur every couple
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shell commands), the CONFIG_IGNORE_NMI flag will take care of that.
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Various Pentium machines have had serious problems with the FPU test in
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bugs.h. Basically, the machine hangs after the HLT test. This occurs,
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as far as we know, on the Pentium-equipped 85s, 95s, and some PC Servers.
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The PCI/MCA PC 750s are fine as far as I can tell. The ``mca-pentium''
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boot-prompt flag will disable the FPU bug check if this is a problem
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with your machine.
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The model 80 has a raft of problems that are just too weird and unique
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to get into here. Some people have no trouble while others have nothing
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but problems. I'd suspect some problems are related to the age of the
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average 80 and accompanying hardware deterioration, although others
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are definitely design problems with the hardware. Among the problems
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include SCSI controller problems, ESDI controller problems, and serious
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screw-ups in the floppy controller. Oh, and the parallel port is also
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pretty flaky. There were about 5 or 6 different model 80 motherboards
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produced to fix various obscure problems. As far as I know, it's pretty
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much impossible to tell which bugs a particular model 80 has (other than
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triggering them, that is).
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Drivers are required for some MCA memory adapters. If you're suddenly
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short a few megs of RAM, this might be the reason. The (I think) Enhanced
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Memory Adapter commonly found on the model 70 is one. There's a very
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alpha driver floating around, but it's pretty ugly (disassembled from
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the DOS driver, actually). See the MCA Linux web page (URL below)
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for more current memory info.
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The Thinkpad 700 and 720 will work, but various components are either
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non-functional, flaky, or we don't know anything about them. The
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graphics controller is supposed to be some WD, but we can't get things
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working properly. The PCMCIA slots don't seem to work. Ditto for APM.
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The serial ports work, but detection seems to be flaky.
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Credits
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=======
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A whole pile of people have contributed to the MCA code. I'd include
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their names here, but I don't have a list handy. Check the MCA Linux
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home page (URL below) for a perpetually out-of-date list.
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=====================================================================
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MCA Linux Home Page: http://glycerine.itsmm.uni.edu/mca/
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Christophe Beauregard
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chrisb@truespectra.com
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cpbeaure@calum.csclub.uwaterloo.ca
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=====================================================================
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Appendix A: Sample /proc/mca
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This is from my model 8595. Slot 1 contains the standard IBM SCSI
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adapter, slot 3 is an Adaptec AHA-1640, slot 5 is a XGA-1 video adapter,
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and slot 7 is the 3c523 Etherlink/MC.
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/proc/mca/machine:
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Model Id: 0xf8
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Submodel Id: 0x14
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BIOS Revision: 0x5
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/proc/mca/pos:
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Slot 1: ff 8e f1 fc a0 ff ff ff IBM SCSI Adapter w/Cache
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Slot 2: ff ff ff ff ff ff ff ff
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Slot 3: 1f 0f 81 3b bf b6 ff ff
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Slot 4: ff ff ff ff ff ff ff ff
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Slot 5: db 8f 1d 5e fd c0 00 00
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Slot 6: ff ff ff ff ff ff ff ff
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Slot 7: 42 60 ff 08 ff ff ff ff 3Com 3c523 Etherlink/MC
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Slot 8: ff ff ff ff ff ff ff ff
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Video : ff ff ff ff ff ff ff ff
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SCSI : ff ff ff ff ff ff ff ff
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/proc/mca/slot1:
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Slot: 1
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Adapter Name: IBM SCSI Adapter w/Cache
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Id: 8eff
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Enabled: Yes
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POS: ff 8e f1 fc a0 ff ff ff
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Subsystem PUN: 7
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Detected at boot: Yes
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/proc/mca/slot3:
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Slot: 3
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Adapter Name: Unknown
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Id: 0f1f
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Enabled: Yes
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POS: 1f 0f 81 3b bf b6 ff ff
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/proc/mca/slot5:
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Slot: 5
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Adapter Name: Unknown
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Id: 8fdb
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Enabled: Yes
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POS: db 8f 1d 5e fd c0 00 00
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/proc/mca/slot7:
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Slot: 7
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Adapter Name: 3Com 3c523 Etherlink/MC
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Id: 6042
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Enabled: Yes
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POS: 42 60 ff 08 ff ff ff ff
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Revision: 0xe
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IRQ: 9
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IO Address: 0x3300-0x3308
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Memory: 0xd8000-0xdbfff
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Transceiver: External
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Device: eth0
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Hardware Address: 02 60 8c 45 c4 2a
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