139 lines
5.4 KiB
Plaintext
139 lines
5.4 KiB
Plaintext
Linux for the Q40
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=================
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You may try http://www.geocities.com/SiliconValley/Bay/2602/ for
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some up to date information. Booter and other tools will be also
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available from this place or http://ftp.uni-erlangen.de/pub/unix/Linux/680x0/q40/
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and mirrors.
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Hints to documentation usually refer to the linux source tree in
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/usr/src/linux/Documentation unless URL given.
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It seems IRQ unmasking can't be safely done on a Q40. IRQ probing
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is not implemented - do not try it! (See below)
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For a list of kernel command-line options read the documentation for the
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particular device drivers.
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The floppy imposes a very high interrupt load on the CPU, approx 30K/s.
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When something blocks interrupts (HD) it will lose some of them, so far
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this is not known to have caused any data loss. On highly loaded systems
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it can make the floppy very slow or practically stop. Other Q40 OS' simply
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poll the floppy for this reason - something that can't be done in Linux.
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Only possible cure is getting a 82072 controller with fifo instead of
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the 8272A.
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drivers used by the Q40, apart from the very obvious (console etc.):
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drivers/char/q40_keyb.c # use PC keymaps for national keyboards
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serial.c # normal PC driver - any speed
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lp.c # printer driver
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genrtc.c # RTC
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char/joystick/* # most of this should work, not
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# in default config.in
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block/q40ide.c # startup for ide
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ide* # see Documentation/ide/ide.rst
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floppy.c # normal PC driver, DMA emu in asm/floppy.h
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# and arch/m68k/kernel/entry.S
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# see drivers/block/README.fd
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net/ne.c
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video/q40fb.c
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parport/*
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sound/dmasound_core.c
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dmasound_q40.c
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Various other PC drivers can be enabled simply by adding them to
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arch/m68k/config.in, especially 8 bit devices should be without any
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problems. For cards using 16bit io/mem more care is required, like
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checking byte order issues, hacking memcpy_*_io etc.
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Debugging
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=========
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Upon startup the kernel will usually output "ABCQGHIJ" into the SRAM,
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preceded by the booter signature. This is a trace just in case something
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went wrong during earliest setup stages of head.S.
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**Changed** to preserve SRAM contents by default, this is only done when
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requested - SRAM must start with '%LX$' signature to do this. '-d' option
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to 'lxx' loader enables this.
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SRAM can also be used as additional console device, use debug=mem.
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This will save kernel startup msgs into SRAM, the screen will display
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only the penguin - and shell prompt if it gets that far..
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Unfortunately only 2000 bytes are available.
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Serial console works and can also be used for debugging, see loader_txt
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Most problems seem to be caused by fawlty or badly configured io-cards or
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hard drives anyway.
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Make sure to configure the parallel port as SPP and remove IRQ/DMA jumpers
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for first testing. The Q40 does not support DMA and may have trouble with
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parallel ports version of interrupts.
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Q40 Hardware Description
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========================
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This is just an overview, see asm-m68k/* for details ask if you have any
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questions.
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The Q40 consists of a 68040@40 MHz, 1MB video RAM, up to 32MB RAM, AT-style
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keyboard interface, 1 Programmable LED, 2x8bit DACs and up to 1MB ROM, 1MB
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shadow ROM.
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The Q60 has any of 68060 or 68LC060 and up to 128 MB RAM.
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Most interfacing like floppy, IDE, serial and parallel ports is done via ISA
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slots. The ISA io and mem range is mapped (sparse&byteswapped!) into separate
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regions of the memory.
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The main interrupt register IIRQ_REG will indicate whether an IRQ was internal
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or from some ISA devices, EIRQ_REG can distinguish up to 8 ISA IRQs.
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The Q40 custom chip is programmable to provide 2 periodic timers:
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- 50 or 200 Hz - level 2, !!THIS CAN'T BE DISABLED!!
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- 10 or 20 KHz - level 4, used for dma-sound
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Linux uses the 200 Hz interrupt for timer and beep by default.
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Interrupts
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==========
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q40 master chip handles only a subset of level triggered interrupts.
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Linux has some requirements wrt interrupt architecture, these are
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to my knowledge:
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(a) interrupt handler must not be reentered even when sti() is called
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from within handler
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(b) working enable/disable_irq
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Luckily these requirements are only important for drivers shared
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with other architectures - ide,serial,parallel, ethernet.
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q40ints.c now contains a trivial hack for (a), (b) is more difficult
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because only irq's 4-15 can be disabled - and only all of them at once.
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Thus disable_irq() can effectively block the machine if the driver goes
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asleep.
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One thing to keep in mind when hacking around the interrupt code is
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that there is no way to find out which IRQ caused a request, [EI]IRQ_REG
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displays current state of the various IRQ lines.
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Keyboard
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========
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q40 receives AT make/break codes from the keyboard, these are translated to
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the PC scancodes x86 Linux uses. So by theory every national keyboard should
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work just by loading the appropriate x86 keytable - see any national-HOWTO.
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Unfortunately the AT->PC translation isn't quite trivial and even worse, my
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documentation of it is absolutely minimal - thus some exotic keys may not
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behave exactly as expected.
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There is still hope that it can be fixed completely though. If you encounter
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problems, email me ideally this:
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- exact keypress/release sequence
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- 'showkey -s' run on q40, non-X session
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- 'showkey -s' run on a PC, non-X session
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- AT codes as displayed by the q40 debugging ROM
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btw if the showkey output from PC and Q40 doesn't differ then you have some
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classic configuration problem - don't send me anything in this case
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