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