Brasstacks

I made a little exercise out of compacting the example "switch debounce" code that the PIC tutorial examples uses. My next exercise will be to improve the debouncing in the "reverse variable speed LED rotation by pressing switch" by interleaving the debouncing check into the delay loop. As it stands, when the rotation is slow, the example can miss brief switch pushes. My glorious savings of three instructions is documented on a separate page . One nifty trick I found through Google that might be very helpful if I have to debounce 88 keys on a Symbolics keyboard (naturally, the same number as on a piano) is called " vertical counters ." This consists basically of replacing counter increments with boolean operations, which can be easily performed in parallel, if the corresponding bits for multiple counters are grouped in register-sized words. This page shows how to use a four-count two-bit vertical counting scheme to debounce eight switches in paralle...

A few comments about the PICkit 2 learning experience. There's a slight bit of polish that could be applied to the example code. A few redundant instructions, such as Extraneous operations setting register pages In A-to-D examples, the data sheet seems to say the 5 microsecond settling time is needed only when changing the input source, not for every conversion, as in the examples For the 5 microsecond interval, a few of those microseconds are covered by the non-NOP instructions before the conversions In one of the variable-speed rotating bits examples, the carry flag is not explicitly cleared when it needs to be clear. When I modified the example to change the sign of the pot setting-to-delay conversion, I would sometimes set the carry, putting extra bits into the display. Took me a good fifteen minutes to debug that. I think a few extra instructions are wasted using the W register and an explicit move to the file register when the file register destination could be...

My latest diversion is a Microchip PICkit2. The idea is to make something that can understand the Symbolics keyboard I have, and then connect that something to other things that can speak Apple Desktop Bus (ADB), PS/2 keyboard protocol, or USB, in roughly that order. If I can make something that takes a multi-button PS/2 mouse and a Symbolics keyboard and connects both to a MacIvory, I could be set for beautiful three-button mousing and classic keyboarding on my Lisp Machine. I've mostly traced out the schematic of my Rev. C Symbolics slim-line keyboard (thank god for simple two-layer boards!). Rev. C has LED's in the Caps Lock and Mode Lock keys, in contrast to this picture of the similar Symbolics Rev. B keyboard . Compared to the Symbolics 3600 keyboard schematic , mine is roughly similar, but unfortunately has a 40-pin microcontroller (an Intel 8749H, a member of the MCS-48 family) soldered in. I am certain I could make something work with the simple protocol the 3600 key...

I've only had a bit of time to play with my MacIvory, but already things are getting interesting. One is getting used to the system administration style: typical UNIX system configuration resides in text files, and the boot process reads them. Genera is different. The state of the system is contained in the memory image ("world"); you change it through various operations---some interactive, some by loading Lisp files---and preserve it by saving a new world as a file, which can be defined incrementally based on an existing world. The boot process involves loading that saved file back into the living Lisp machine. I haven't yet developed the sense to complete a block of tasks before saving the world, and how much change pushes one from incremental to a complete world. Another was getting the network to speak, and part of that is the timewarp of working in Mac OS 7, an era in which Mac networking was going through the introduction of Open Transport, and an AppleTalk era ...