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MRT
Account closed
Registered: Sep 2005
Posts: 149 |
2 bit irq loader
Hmm, just a question...
Is there a 2 bit irq loader, which doesn't require blocking other interrupts while loading a byte?
i.o.w. Is there a realy fast irq loader which doesn't block any interrupts and let me use my beloved sprites? :-)
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MRT
Account closed
Registered: Sep 2005
Posts: 149 |
Ok...
But, does anyone has expirience with the usage of these loaders? I don't mean the implementation, but more the workings. Because you can't have more than one drive connected, does this give a lot of users problems?
b.t.w: I always thought that to setup atn, would also require specific timing... and therefor didn't work too well with sprites/badlines |
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hollowman
Registered: Dec 2001
Posts: 474 |
the user problems i've experienced are usually more about "loader x doesnt work on my drive y" |
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JackAsser
Registered: Jun 2002
Posts: 2014 |
@MRT: ATN is simply yet another line which the C64 can control. So, with 2bit+atn you simply let ATN become your clock reference and uses DATA+CLK as pure data lines instead. This way you can asyncronously (no problems with timing since ATN is the clock) send 2bits at a time.
If you instead do synchronous transfer, i.e. when timing IS a problem, then I guess you in theory could use all three lines as data lines and thus send three bits per write, however that feels a bit messy. This however only works from C64->Drive since it's only the C64 who can drive the ATN line.
Another way is to do semi-synchronous transfer. First you synchronize for instance per byte using ATN, then you synchronically burst 8 bits using DATA+CLK, i.e. 2 bits at a time.
Blah blah blah crap talk crap talk... :D |
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Cruzer
Registered: Dec 2001
Posts: 1048 |
What's the fastest IRQ loader, which just have to work for a standard PAL C64 + 1541? |
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cadaver
Registered: Feb 2002
Posts: 1160 |
Don't know the answer, but there should be no reason that a PAL-only loader would be faster than one which can adjust the C64 side code to work with both PAL & NTSC (since the drive runs at same speed anyway) |
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MagerValp
Registered: Dec 2001
Posts: 1078 |
The speed largely depends on how fast the drive code can decode GCR data, how it handles interleave, and what the C64 loader does while waiting. Krill has an interleave-less loader (i.e. it reads the next sector out of order, and assembles on the C64 side) that also decrunches while waiting for the drive to read and decode the next sector. I had an idea earlier for a custom GCR format that should virtually eliminate decoding time that I think he's going to incorporate. So if you want something really fast, check with Krill...
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Ninja
Registered: Jan 2002
Posts: 411 |
The question about the fastest loader is a bit like the one about the best cruncher or assembler. It depends heavily on your needs and requirements. |
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algorithm
Registered: May 2002
Posts: 705 |
Also.. Fastest loader + tightest data compressor=quicker loading |
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Cruzer
Registered: Dec 2001
Posts: 1048 |
Quote: The question about the fastest loader is a bit like the one about the best cruncher or assembler. It depends heavily on your needs and requirements.
Ok, how about...
- It has to work with a C64 + a 1541, and doesn't have to work on other drives.
- It loads 16 blocks ($1000) of code, which can't really be compressed much, so let's say it's not compressed.
- One IRQ each frame for playing music, and doing simple stuff like switching some text. The IRQ will use up to 48 ($30) rasterlines.
- No need for cycle excact timing. Actually the IRQ could vary several rasterlines if that would make the loader faster.
- No sprites on the screen.
Wonder if it would be possible to use all 3 bits for data transfer for a loader with these kinda requirements. |
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JackAsser
Registered: Jun 2002
Posts: 2014 |
@Cruzer: Only the C64 can control the ATN line so you can't make use of all three bits as data bits when sending from 1541->C64 (loading). Saving could in theory ofcourse make use of it. :D World's fastest hiscore saver anyone? :D |
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