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Stirf
Account closed
Registered: May 2002
Posts: 26 |
coding with C128
I have a C128 (Not not the desktop version) now and want to use it for coding, preferably using Turbo-Assembler.
How can I use to use the advantages new in Commodore computer?
Are there any specially modded assembler versions for this machine?
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iopop
Registered: Dec 2001
Posts: 317 |
Target c128 or c64?
if c64, I know that Lynchbit made some mods on Turbo asm which used the VDC mem on the c128 to temporarily save the source+asm in the VDC when running your code. (Similar to FLT's REU mods of tasm.) However, you need to have 64k VDC installed on your c128, which not all have, so be sure to check that out.
Leech it here: http://rr.c64.org/bin/codeorg2&3.zip |
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Stirf
Account closed
Registered: May 2002
Posts: 26 |
What is a VDC and how can I obtain one?
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Steppe
Registered: Jan 2002
Posts: 1510 |
Every C128 has a VDC, 'tis a video chip for the 80 coloumns mode, you know. :-)
The flat 128 and the plastic case desktop do have 16 KB of VDC mem, the metal cased 128D already has 64 KB of VDC mem. However you can mod the other two 128 revisions to have 64 KB as well. Read here:
http://www.floodgap.com/retrobits/ckb/display.cgi?161 |
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Oswald
Registered: Apr 2002
Posts: 5029 |
I've been coding using this method since '96. Its pretty handy. The VDC assembler, is able to assemble into the 64k vdc chip, after that you have to run a little routine wich swaps the "normal" and the vdc ram. So u can use all 64k for testing code.
the swap routine that comes with it, is quite slow, I've managed to speed it up so it takes about, but rather less than 2 seconds to swap the 2 ram.
Eventhough the VDC has only 2 visible registers mapped in the IO area, you might LOSE source due to buggy code. Buggy code might write random values into the regs so, that you cannot swap back the VDC ram (source) correctly. This happens rarely though.
I keep my swap routine somewhere at $08xx, and I only swap the memory $0900-ffff, so if your code does not overwrite it, you can have the swapper in the memory alway, and switch between "source"-"object" "bank" easily. |
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Krill
Registered: Apr 2002
Posts: 2855 |
damaging data in the expansion memory also happens using a reu and a reu-based assembler. still it depends on certain ways of implementation, how vulnerable it is to broken code going berserk. f.e. tron/fairlight's reu turbo assembler version is more vulnerable to that than sputnick's virtual assembler, imho because the tron assembler relies on swapping stuff, while sputnick's only copies stuff into the c64's memory, minimizing actual swapping. |
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Stirf
Account closed
Registered: May 2002
Posts: 26 |
The C128 VDC mod seems do-able for someone like me, mostly because the old ram can be cut away and be discarded.
I will try it, I don't have much to lose because I still have the good old C64.
Thanks people! |
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Graham
Account closed
Registered: Dec 2002
Posts: 990 |
btw one thing i always wondered: does vdc tasm set a valid vdc screenmode? else the vdc will have problems doing the ram refresh. |
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Oswald
Registered: Apr 2002
Posts: 5029 |
Graham:
dont think so, the vdc rams works without that, u just have to turn on the machine.
My fastest swap routine turned everything down to minimum (0 rows/0 columns/monochrome/ slowest ram refrsh rate/etc) and it didnt even need to wait for the vdc to signal wether it had finished to read/write a byte. But this is heavily ram type dependent. After succesfully burning the VDC ram, and having it replaced the new rams did not work with the slowest refresh rate, I had to go back and use an older, slower swap routine. |
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Graham
Account closed
Registered: Dec 2002
Posts: 990 |
@Oswald: i wouldnt trust that. the ram used for the vdc is standard DRAM which absolutely needs a constant refreshing to safely keep its data. to ensure the presence of a useable ram refresh you must set a screenmode and also set a refresh rate which applies to the specs of the drams. this would be 5 refresh cycles per rasterline if you use 15khz horizontal frequency. |
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JackAsser
Registered: Jun 2002
Posts: 1994 |
Speaking of memory refresh. At work I started to code my own BIOS for our hardware. When I got the memory to work and the setup a gfx mode I drew a stipple pattern into the framebuffer (which resides in the RAM). Then I removed the so-dimm module and waited 30 seconds. Reprogrammed the BIOS so that it doesn't generate a new pattern, but uses what's in memory. When I reinserted the so-dimm module all data was OK, it took about 3 minutes before the data slowly got corrupted.
Quite cool actually. So, what about those old memories in the VDC, how strong are the static charges in those and for how long can it keep it's memory without power? |
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