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Krill
Registered: Apr 2002
Posts: 2825 |
Release id #167152 : Krill's Loader, repository version 164
If no problems emerge (i know they will, but anyways)... I can explain a bit about the full on-the-fly GCR block read+decode+checksumming. |
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Smasher
Registered: Feb 2003
Posts: 512 |
first test: I compiled this amazing loader trying all supported packers.
this is the length of the compiled file "loader-c64.prg" (no raw load):
BITNAX: $29d
BYTEBOOZER: $2a2
DOYNAX: $2bb
EXOMIZER: $370
LEVELCRUSH: $2be
NUCRUNCH: $2d9
PUCRUNCH: $324
SUBSIZER: $384
TINYCRUNCH: $1f2
so you can import the resident at $0100-$03ff (assuming that's a smart place where to put it) with some packers, but not with all of them.
I hope this info could be useful for someone... I'll now dedicate some time on the speed tests. |
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Krill
Registered: Apr 2002
Posts: 2825 |
Bitnax should be $0280 and tinycrunch $01d5, as advertised. Seems like you've left LOAD_RAW_API enabled.
The best place to fit the resident part is so that it ends at $03ff incl.
That way, you have as much stack space left as possible and can still use $0400 for screen memory.
This obviously doesn't work for the meatier decrunchers, as the resident portion is close to or bigger than $0300 bytes with them.
As for speed, tinycrunch should be fastest, followed by Bitnax, then Doynax-LZ.
This is because these three have a block-based read-data interface, as opposed to having a JSR for every incoming byte of the packed file. |
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Smasher
Registered: Feb 2003
Posts: 512 |
mmmh, yes it could be I left RAW enabled in "config.inc". I'll recheck that later tonite. enabling or disabling that API just changes the compiled size, but no impact on the speed, correct?
or a better question (since I don't want to play with all the settings): only NTSC_COMPATIBILITY has impact on the speed performance AFAYK?
yes, even if tinycrunched files are ~2x bigger than exomized ones it seems your loader is way faster with TC! |
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Krill
Registered: Apr 2002
Posts: 2825 |
Right, LOAD_RAW_API should have no or minimal impact on speed.
The options which do make it somewhat slower are NTSC_COMPATIBILITY, as you said, and also LOAD_UNDER_D000_DFFF and LOAD_VIA_KERNAL_FALLBACK.
Exomizer, despite big speed improvements from version 2 to 3, is still among the or the slowest one.
For tinycrunch vs. *nax, it may depend more on the actual corpus of test files what's faster with combined loading + depacking. The pack ratio diff vs. depacking speed diff ratio may or may not tilt the scale in favour of one or the other, depending on the actual file. |
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Sparta
Registered: Feb 2017
Posts: 38 |
Krill, first of all congratulations, your loader is truly a masterpiece. I spent considerable time with deciphering it and I think now I understand what you are doing. The GCR loop is an amazing feat. One of its major advantages vs checksum verification integrated in either side of the transfer loop is that you do not need to wait with changing tracks until after transfer of the last block in a track is completed. Shrydar stepping cuts the delay to 12 bycles. This, however, can be completely eliminated. The following (Spartan) method provides a seamless and uninterrupted transfer of data across neighboring tracks. This is how it works in the latest version of my loader developed for personal use:
lda $1c00 //First half-track step
sec
rol
and #$03
eor $1c00
sta $1c00 //Update VIA 2 Port B
sec //Calculate second half step...
rol
and #$03
eor $1c00
sta LastStep+1 //…and save it for later
Then start data transfer immediately:
ldy #$00
…
lsr
dey
TrBranch: bmi Loop //Send #$81 bytes first, then the remaining #$7f
bit $1800
bpl *-3
sta $1800 //Last 2 bits completed
lda #$d0 //Replace "BMI" with "BNE"
sta TrBranch
LastStep: lda #$00
sta $1c00 //Update VIA 2 Port B
cpy #$00 //
bne Loop2 //Back to transfer if not done
//C64 loop has a similar delay built in
This can be adopted to almost any transfer loop reducing delay to a few cycles. |
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Krill
Registered: Apr 2002
Posts: 2825 |
Sparta: Thanks! :)
I've considered something like your method (Spartan Stepping :D), but ultimately decided against it.
Its central concept is issueing the second half-track step in the middle of the block transfer.
However, this poses a few problems in a general-purpose standard format loader:
- The computer-side resident code needs to be aware of the slight delay in the middle and wait accordingly, which would increase resident code size ("C64 loop has a similar delay built in", as commented in your example).
- The computer-side code needs to be aware that the currently-transferred block is, indeed, the final file block of the current track, otherwise the extra delay would be in vain (and possibly a net loss due to just-missed following blocks). This would increase resident code size and also require that information to be sent to the resident code somehow, meaning extra protocol overhead.
- The drive-side code is extremely tight as it is (tightest code i ever made, and i've squeezed and squeezed again to fit in everything i needed to fit). It might not be possible to use this approach without throwing out some other functionality. |
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Sparta
Registered: Feb 2017
Posts: 38 |
Yes, you got it. Spartan stepping uses the transfer loop to pace half-track steps instead of a timer. :)
I respectfully disagree with your second point. The computer-side code does not need to know whether the currently transferred block is the final block of a track. Thus, code can be simplified. Fetching and transferring a block takes roughly 27000-29000 cycles depending on speed zones. Spartan stepping adds 17 cycles to this (72 vs. 72.06 bycles/block transfer). I do not think this causes a significant delay resulting in missing the next block. The total loss while loading a full 35-track disk is 664*17= 11288 cycles, spread out evenly. Shrydar stepping, on the other hand, adds 12*256*34=104448 cycles delay. The difference is about 10-fold.
After the on-the-fly GCR loop and the 72-cycles/byte transfer loop, Spartan stepping was the first thing that resulted in a significant speed improvement in my loader.
I can see your point in your third comment. Your code's complexity-to-tightness ratio is extremely high. :) |
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ChristopherJam
Registered: Aug 2004
Posts: 1370 |
shrydar here.
Yes, I have wondered about doing a half track step mid transfer too, but I think the pertinent performance metric is percentage time saved, which even at interleave of three is only 0.5% (3072 cycles every 600,000 - and that's assuming no errors, and either perfectly aligned tracks or out of order loading).
Either shrydar stepping or spartan stepping is a huge improvement over the old "wait until you're about to try and read the next block, then spend 60+ bycles on stepping and stabilisation" mind. The biggest win is almost certainly from allowing the head to settle during the transfer.
I'm still undecided about when to do the second step in Marmaload; my own loader development's been on hold while I've been distracted by crunchers and demo effects.
At this rate I suspect that'll remain the case until I've at least one production out the door using Krill's instead - we'll see :) |
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Krill
Registered: Apr 2002
Posts: 2825 |
Quoting SpartaI respectfully disagree with your second point. The computer-side code does not need to know whether the currently transferred block is the final block of a track. You're probably right there. But the first and third points alone seem to prohibit Spartan Stepping in my case. And yes, what Shrydar aka ChristopherJam said. :) |
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Sparta
Registered: Feb 2017
Posts: 38 |
Quoting ChristopherJamThe biggest win is almost certainly from allowing the head to settle during the transfer.
Agreed on this. In my loader Sparkle, which will never be as versatile as Krill's, I think I am going to settle (huh) with the best of both worlds. I.e. I will time the second half-track step in the transfer loop about 12 bycles after the first one to allow enough time for the head to settle. Call it the Spartan Shrydar Step. :))
P.S. I was aware of the mysterious Shrydar's identity. Google knows everything. :) |
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