Handling Input for Amiga Demos

Keyboard Timings

If you have to read the keyboard by hardware, be very careful with your timings. Not only do different processor speeds affect the keyboard timings (for example, in the game F-15 II Strike Eagle on an Amiga 3000 the key repeat delay is ridiculously short, you ttyyppee lliikkee tthhiiss aallll tthhee ttiimmee. You use up an awful lot of Sidewinders very quickly!), but there are differences between different makes of keyboard, some Amiga 2000's came with Cherry keyboards, these have small function keys the same size as normal alphanumeric keys - these keyboards have different timings to the normal Mitsumi keyboards.

Use an input handler to read the keyboard. The Commodore guys have spent ages writing code to handle all the different possible hardware combinations around, why waste time reinventing the wheel?

Beware bogus input falling through to Workbench

If you keep multitasking enabled and run your own copperlist remember that any input (mouse clicks, key presses, etc) fall through to the workbench. The correct way to get around this is to add an input handler to the IDCMP food chain (see - you *do* have to read the other manuals!) at a high priority to grab all input events before workbench/cli can get to them. You can then use this for your keyboard handler too (no more $bfexxx peeking, PLEASE!!!)

Look at the sourcecode for Protracker for an excellent example of how to do the job properly. Well done Lars!

Hardware Differences

The A1200 has a different keyboard to older Amigas. One of the side effects of this is it appears that older hardware-hitting keyboard read routines are not able to register more than one keypress at a time. I currently do not know whether this is a limitation in hardware and if it is possible to read multi-key presses (excepting the obvious CTRL/ALT/SHIFT type combinations) at all... A bit annoying for games writers I would think.

If you now are using you own hardware and Interrupts to read the keyboard on faster computers, make sure you ALWAYS have the given time-delay for ALL keyboards you want your program to work with (The delay between or.b #$40,$bfee01 and or.b #$40,$bfee01)! Don't trust delay loops since the cache can speed those up rather drastically! I have seen too many, even commercial, programs that just ignores this and have NO delay code or just a simple dbf-loop. After about 15 keypresses your keyboard is dead and there is no code to reset it. If you can - skip having your own keyboard routines, since they mostly fail anyway.

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