On 8/10/10, Daniel Kahlin <firstname.lastname@example.org> wrote: > > On Tue, 10 Aug 2010, Anders Carlsson wrote: > >> Daniel Kahlin wrote: >> >>> Anyway a quick analysis shows that the game loads $027A-$2000. The first >>> chunk at $027A looks like a cassette header indicating a file "FLASH $027A- $028E are full of file parameters (type of program, start/end addresses, filename, etc) when saving anything on Tape #1 (not sure about Tape #2 without checking the code). >> While I haven't studied the PET memory map recently, isn't $03FD part of >> the cassette buffer? No. Tape #1 buffer: 027A-0329 Tape #2 buffer: 033A-03F9 $03FD-$03FF are outside of the tape buffers. >>If so, perhaps the computer rebuilds that part of memory >> when you save in a normal way, and you lose whatever was there. On BASIC 4 machines, there is quite a bit of mucking around in the Tape #2 buffer (check any memory map). I didn't own a BASIC 4 PET when I was using tapes, so I never had those locations stepped on, but if you happen to be using BASIC 4 for this tape manipulation, it's possibly that it could be part of your problem. > From what I can tell it isn't part of the cassette buffer. Judging from > the flash attack file there is space for two cassette buffers. > One from $027A-$0339 and one from $033A to $03F9. > Though, the layout in the flash attack file could be a decoy. > > I'm leaning towards that there might be a different low limit for tape > saving on the PET. IIRC this limit is $0300 on the C64 and VIC20. Back in the day when I used BASIC 2 PETs and tape drives every day, I used to write a lot of code for the second cassette buffer. I don't remember having any hassles with loading or saving it via TIM. I also never fiddled whatsoever with anything in the first cassette buffer since you can't load or save that memory with that tape drive - you'd essentially need to save data in the first cassette buffer via a drive plugged into the secondary port (the outside port on original chicklet PETs or the inside port on dynamic PETs) or save to disk (which I didn't have back then). When writing hybrid programs (ML and BASIC) I used to use TIM to save the second cassette buffer _and_ BASIC programs as a unit, but it was using the standard commands, with the start address of $033A and the end address of however far into main memory the BASIC code went. As for "low limits", the C-64 and VIC-20 are different from the PET because they only have one cassette buffer, so you can't use one drive to save the contents of the other drive's buffer area. On the PET, this was done routinely. -ethan Message was sent through the cbm-hackers mailing listReceived on 2010-08-10 15:00:38
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