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 ben's20 bit cpu. 
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Joined: Mon Oct 07, 2019 1:26 pm
Posts: 41
Hi Ben, I'm looking for a simple OS for my Kobold computer. It's a computer with 20 address lines, so around the same size as yours.

That OS that you use, does it have free C source ? And/or did you make it yourself ? Would you recommend it ?

Sun Jun 14, 2020 6:32 pm

Joined: Mon Oct 07, 2019 2:41 am
Posts: 118
It is my own os, but written in my own language so it rather not portable to other
machines because of the way subroutines are called. Frame based rather than stack based.
The compiler and the assembler are both written in C ("USS Enterprise NCC 1701. No bloody A-B-C-D or E!" Scotty).
The os is a simple CP/M style os, using a block size of 1526 bytes (3 512 byte sectors).
I have a fat table of one sector and directory of one block. This gives ample space for
the I/O at the time (1975-1980) using GCR. The simple OS is placed in
the last 64Kb of memory and the bottom memory is used for programs.
I have 1KB bios that provides the basic I/O read char / write char / read block write
block,boot from paper tape,boot from disk.
The OS is written in 4 segments, so I have bootstrap version and the DOS using
the same code, with just a few routines in the main body.

Sun Jun 14, 2020 7:24 pm

Joined: Mon Oct 07, 2019 2:41 am
Posts: 118
Here are the files. This is for a 8/16/32 bit cpu
This software requires a CPU with a long branches
and set ac to 0/1 on condition codes. is the bengol compiler + microcode test
cpu.lst (txt) is the microcode roms is the os written in bengol
The bengol compiler is being revised to make it easy to port
simple c programs. { after a function define C like operands
other wise a algol like syntax begin end if eif else endif while repeat
do until. Structures are defined as offset to a array

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Sun Jun 14, 2020 8:46 pm

Joined: Mon Oct 07, 2019 2:41 am
Posts: 118
Now upgrading the hardware this week, for the 20 bit cpu. Moving the SD card from the DE1
to the expansion bus using Sparkfun's SD card adaptors, once FedEx delivers them.WOW 2
1970 IBM 2315 disk cartridge drives (software emulated). 32K words ram make this a MID SIZED
micro computer. ( still need to add more serial ports and printer ).

Tweeking the hardware for BCD floating point routines, and some general software revsions
as well.
I have come to the conclusion that 12K (words) is needed for the OS and I/O buffers+ Stack.
24 K (words) is needed for program space. CP/M got away with a small footprint by having 128 byte
sectors and the user program handles buffer and stack space. Flex (6800) had 256 byte sectors
and a 8K footprint. Apple and the other machines had a 'ROM BASIC' O/S.
12/16 bit machines had fancy DMA Discs that swapped core and disk to give virtual memory
and often timesharing in 16K words.

Thu Aug 06, 2020 5:32 pm
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