Z80 REPL (2018)

99 pointsposted 5 hours ago
by adunk
(abagames.github.io)

12 Comments

flyinghamster

3 hours ago

The one thing I lamented about the Apple II Plus (vs. the original with Integer BASIC) was that to make room for autostart, they had to rip out the mini-assembler in the Monitor ROM. That was the closest thing I ever saw to an assembly-language REPL before this. At least they were able to keep the disassembler.

EvanAnderson

2 hours ago

I remember being so confused, as a 10 y/o kid, trying to follow examples from an Apple II-era book on my public library's Apple IIe computers. I didn't understand why I couldn't get the mini assembler to work. The idea that features would be removed on future machines simply didn't occur to me. I guess I really didn't even understand that the IIe was a different machine than what the book was written for since most everything else worked as-expected.

kevin_thibedeau

31 minutes ago

The mini-assembler was still available from Integer BASIC on II+ and IIe. It returned to ROM for later IIe models.

boomlinde

2 hours ago

It's common in the C64 world to use freezer cartridges that allow you to interrupt normal operation and invoke a monitor program. These typically include rudimentary assemblers and disassemblers as well. Fun and useful for patching and reverse engineering!

boomlinde

an hour ago

Btw, I've only had a rough idea of how these are actually implemented, non-maskable interrupt something-something, and never knew how they make sure that the interrupt vector points to some persistent routine that can invoke the monitor. I found this great article explaining at least how The Final Cartridge 3 does it (in the first two sections): https://www.pagetable.com/282

abecedarius

2 hours ago

I felt the same way.

There was another downside, that the Applesoft BASIC license gave Microsoft a hostage which they later used to kill https://en.wikipedia.org/wiki/MacBASIC. Hard to tell how much it mattered that the Mac came with no user programmability, which had been expected for PCs till then.

Gracana

20 minutes ago

Wow, somehow I didn't know about this. Now I'm angry, bundling an official Macintosh BASIC on every computer would have been huuuge for young-me.

networked

3 hours ago

Cool idea! The REPL needs to handle whitespace after an instruction with no operands:

  > ld c,20h
  0E 20   (7 cycles)
  > ld c,20h [<-- trailing space here]
  0E 20   (7 cycles)
  > nop
  00      (4 cycles)
  > nop [<-- trailing space here]
  unknown instruction: nop
I also wish I could select from the completion list with Tab without typing more of the instruction, fish-style. I.e., you press Tab to go through completion 1, completion 2, ..., completion N, completion 1 again with Enter to confirm your pick.

j4cobgarby

3 hours ago

Really nice! Would be fun if there were a few examples that could be loaded into memory

torutofu

3 hours ago

the fun part is how fast you can get back into Z80 muscle memory once the repl is giving you immediate feedback