I've been reading the source code to SBC OS to better understand how a ROM monitor works. The memory map claims that page 2 is free above $026f, but I can't figure out what it is using page 2. I know it isn't I/O as that is memory mapped to page $7f.

As an aside I'm writing my own ROM monitor as a learning exercise and realizing that it might be an act of hubris.

Can you provide a link to the SBC OS you are looking at? My SBC2OS uses page 3 for the keyboard input buffer and a few system pointers.

Daryl

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Please visit my website -> https://sbc.rictor.org/

I'm writing my own 65c02 monitor with mini-assembler and disassembler as well, but I'm targeting the Kowalski simulator for development and debugging. It's coming along slowly, but I have yet to decide on how to deal with secondary storage options for a potential "real-hardware" version. Luckily, Daryl and several other kind veterans here have provided fully-coded installations to study, but it will still take some thought on my part to decide if I'll create a set-up that uses block-oriented storage or just a simple stream-oriented storage (maybe both?). I'm not coding from pure scratch, but nothing I study or borrow will survive without extensive modifications by yours truly. It will be paired with VTL02, or a DTC Forth similar to PETTIL, or possibly an enhanced version of Woz BASIC, and should fit easily in 4K of ROM, at least in the case of VTL02.

[OT question for Daryl: Do you have any details of the Kowalski simulator I/O options you could PM to me? At present I'm just using the simulated ACIA from an example I got from Klaus. Are there more built-in I/O options hiding somewhere, documented or otherwise?]

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Got a kilobyte lying fallow in your 65xx's memory map? Sprinkle some VTL02C on it and see how it grows on you!

Mike B. (about me) (learning how to github)

I'm using the copy I got from Rich Cini for his 2.7 respin of the SBC. Here's a link:

http://cini.classiccmp.org/my6502/6502s ... 40_src.zip

Rich took your SBC and added an onboard AVR video and an IEC port interfaced to the existing VIA's. It might be related to buffer space for one or the other, or maybe neither. But I can't figure it out.

Update: In basic23.asm I found a line indicated page 2 is being used for buffer space. So it looks like something for EH Basic.

Yes, EhBASIC is using page 2 for flags and the input buffer. In the patched version, Rich added some file pointers and buffer at $0270. Looks like it uses addresses up to $02B5. The SBC code uses page 3 for input buffer and non-zero page storage.

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Please visit my website -> https://sbc.rictor.org/

Kowalski only has the ACIA terminal for IO emulation. At the bottom of the Help Index, is a page titled IO Functions. It has the 7 IO addresses that affect the IO terminal.

Daryl

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Please visit my website -> https://sbc.rictor.org/