Re: 6502 Multitasking OS announce

[holger@deep.hb.provi.de (Holger Bruns)]

In article <4i94fs$stj@narses.hrz.tu-chemnitz.de> 
fachat@physik.tu-chemnitz.de (Andre Fachat) writes:

>This is the announcement of "OS/A65", a 6502 CPU operating system
>I wrote some time ago and which I now put on the Web. It is
>copyrighted under the GNU public license.

>Some of its features are:

> - preemptive multitasking

> - (kind of) microkernel design

> - filesystems for PC FAT disks and CBM floppy drives on a IEEE488 interface

> - runs on 6502 computer with and without MMU

> - developed on a selfdesigned and -built 6502 computer


>If someone is really interested in, I can also write an article for
>a publication or so about it. But, well, 8 bit times are gone...

Dear Andre,

no, this is not true. Small microcomputers based upon an 8 bit data bus are 
still a good catch for a lot of purposes. I built a 6502 system with 32 kB RAM 
to control my self developed digital audio codec. The system has only a 
bootstrap EPROM, a serial port based upon an 6551 ACIA and some PIA and VIA 
chips to connect a SP/DIF-transceiver, several ADC's and a DAC with my 
microcomputer. The EPROM contains only a very small amount of code. After 
reset, the code reads from the ACIA the program which will be run immediately 
after loading. Since I'm still developing new features, I wrote a simple 
debugger which can be used as a system monitor as well as a core of an 
operating system. As a system monitor my debugger is very similar to popular 
debugging tools like debug (for DOS) and SID (for CPM). As a core of an 
operating system, my debugger is not quite advanced. It has no disk I/O. All 
inputs and outputs must be done with the serial port. But it has some 
procedures which can be invoked from the IRQ signal. The IRQ serves the 
serial I/O and the PIA and VIA chips - like many other 6502 microcomputers.

I have the idea to expand my code to a realtime system with multitasking 
properties, because several operations must be controlled simultanously. I 
shall use a clock signal, which will be generated by one the timers, which are 
themself a part of the VIA chip. Each clock tic generates a time slot. This 
mechanism can easily be used as a base for a multitasking system. 

An operating system for the 6502 should have some of the properties of CPM. 
Parameters could be passed into registers and some zeropage locations. 
The operating system should be invoked with the BRK instruction. This was my 
latest idea. But it seems so far, I am to late. I do not know, if your system 
works in this way, Andre. I have not seen your code until now. But you have 
done the job. My congratulations.

Regards,
Holger Bruns

PS: If anyone wants to get more information about my homebrew 6502 system: 
Please send me a mail. But be warned. The comments of my debugger are written 
in German. I could write an English version, but this would take some time.