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/

  and mirrors.
  
  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
  the 8272A.
  
  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
  		net/ne.c
  		video/q40fb.c
  		parport/*
  		sound/dmasound_core.c
  		      dmasound_q40.c
  
  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.
  
  
  Debugging
  =========
  
  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
  questions.
  
  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
  shadow ROM.
  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.
  
  
  Interrupts
  ==========
  
  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
  asleep.
  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.
  
  Keyboard
  ========
  
  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