Problem to add Philips VG5000 target

Discussion about other targets
stefano
Well known member
Posts: 2137
Joined: Mon Jul 16, 2007 7:39 pm

Re: Problem to add Philips VG5000 target

Post by stefano »

I'm reviving this old topic to announce that I've been able to disassemble the VG-5000 ROM, integrate it with comments, and clean it up enough to recover a valid source program.
I'm not sure it is totally decoded, probably it can't survive (yet) to massive code shiftings, but it is good enough to create byte-identical versions of the V1.0 and 1.1a ROMs. An intermediate 1.1 version existed, with very odd bugs on it on a couple o bytes, I suspect it was consequence of HW errors (e.g. while burning or reading a ROM chip.
The major benefit the new version was the video access speed for the console, which was declared to be three times faster on V1.1.

The interesting aspect is that the entry points were left mostly unchanged, the patches introduced with version 1.1 accurately avoided the problem.

This makes the code a bit cumbersome but the overall firmware is an interesting "missing ring" between the 8K and the Extended BASIC.
It is mostly an 8K (1978) with a little bit of contamination from the M100 and MSX world (1983), a full screen editor (that feature permitting to move up the cursor and edit and re-submit the BASIC lines and commands just entered before), a nice bit-banging PLAY routine, a character conversion table to deal with the MSX printers and a bit of care on the compatibility at source code level with the previous Philips C7420 module.

https://github.com/z88dk/techdocs/blob/ ... vg5000.asm

Building the ROM with the MAP and LST files enabled provides a quick reference to many useful informations, it is now possible to safely rely on the ROM routines to provide a target specific set of brand new functions.
stefano
Well known member
Posts: 2137
Joined: Mon Jul 16, 2007 7:39 pm

Re: Problem to add Philips VG5000 target

Post by stefano »

Short update to tell that I refined the disassembly covering all the ROM and commenting most of it. It's at a very good level, I suggest those programmers understanding the z80 assembly code to have a look ;)
Post Reply