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taper
Registered: Dec 2001
Posts: 119 |
Event id #2391 : The 2015 REU Compo
Welcome to the 2015 REU Compo --- Hosted by LFT, Ruk and Taper!
See the event-page on: The 2015 REU Compo
Your mission is to create the most awesome one-file demo that runs on a standard C64 with a 512 kB REU and no disk drive.
Background
==========
The Commodore RAM Expansion Unit (REU) is a cartridge that provides secondary storage to the C64. It was introduced at CES in 1985. The memory in the REU cannot be accessed directly from the CPU (hence
"secondary"). Instead, the CPU must instruct the REU to transfer a given amount of data to or from the cartridge. The REU then takes over the bus, stalling the CPU, and transfers one byte per cycle.
This is basically all there is to it. Apart from the extra storage, the REU does not make the C64 faster or more powerful---although see below for some intriguing possibilities.
The largest REU available from Commodore (the 1750) was equipped with 512 kB of RAM. Nowadays, it is possible to emulate REUs with as much as 16 MB, e.g. using VICE or the 1541 Ultimate. Even though you can only use 512 kB in this competition, there should be no problems using
the RAM expansion features in the 1541U/1541U-II, Chameleon64 or any other device fully compatible with the Commodore 1750 REU.
Rules
=====
1. Your entry must be in .PRG format with a BASIC header. The file must load to address $801, and end before it reaches the I/O area at $d000. The gives a maximum file size of 51201 bytes.
2. You may assume that a REU of at least 512 kB is available.
3. Your entry must work with a larger REU (i.e. you cannot assume that the upper address bits are ignored). You may not use the extra RAM available in such configurations.
4. You cannot make any assumptions about the initial contents of REU memory.
5. Your entry must work on a real C64 with a real 512 kB REU from Commodore. Please keep in mind that there could still be bugs in the emulators.
6. Deadline is set to 2015-12-31 at 23:59 in a time zone of your choice. Your contribution needs to be mailed to reu@wuff.se to be accepted. You are free to create a CSDb entry for your contribution, else we will do it for you.
7. Immediately following the deadline, voting will take place on CSDb during a period of two weeks. Anonymous votes will be counted. We allow self-voting unless you have multiple personalities.
Suggestions
===========
For your inspiration, here are some ways in which a C64 demo might benefit from an REU:
Obviously, the extra RAM is useful. For instance, the demo might pre-compute large amounts of sprite graphics, and then quickly retrieve a subset of the data just before it's needed.
The fast transfer rate could be used to speed up scrolling operations: You can copy a large bitmap from the C64 to the REU, and then back again at a slightly different address.
Last but not least, the REU has a mode where every byte in a transfer gets written to the same destination address. This can be used to display graphics using the idle byte, for instance. The target address
could also be an I/O register, and this might enable some new VIC tricks.
Technical information
=====================
Please refer to the following documents for details about the REU programming interface:
http://www.zimmers.net/anonftp/pub/cbm/documents/chipdata/progr..
http://codebase64.org/doku.php?id=base:reu_registers
Happy hacking!
/LFT, Ruk & Taper |
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chatGPZ
Registered: Dec 2001
Posts: 11390 |
you forgot CSG8726R1-TechnicalReference-1.0.pdf - which is pretty much the only (mostly) complete and error free doc :) |
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ruk
Registered: Jan 2012
Posts: 43 |
Thanks, Groepaz! |
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Maxlide
Registered: Apr 2003
Posts: 32 |
How are you supposed to get your data into ur machine without a diskdrive? Oo |
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iAN CooG
Registered: May 2002
Posts: 3201 |
tape! apart that, after loading the prg should run with the drive turned off, i guess. |
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chatGPZ
Registered: Dec 2001
Posts: 11390 |
MSE - obviously! |
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T.M.R
Account closed
Registered: Dec 2001
Posts: 749 |
i thought we were discouraged from uploading PRGs here... can the rules have a likkle nudge so T64 is okay too? =-)
(Also... considering options and wondering if the TC's REU is close enough to trust when developing.) |
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chatGPZ
Registered: Dec 2001
Posts: 11390 |
we are working on that just right now =) |
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Oswald
Registered: Apr 2002
Posts: 5095 |
whish the reu was just a little bit more programmable, fex skip every nth byte would help in doing a twister. iirc we had a topic where it was said reu could get rid of the fli bug, well now is the time :) |
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JackAsser
Registered: Jun 2002
Posts: 2014 |
When the VIC needs to steal cycles for DMA, will the currently running REU-DMA simply be halted and resumed after the VIC-DMA? Will the VIC also stall the REU an additional 3c like it does when stalling the CPU? |
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Krill
Registered: Apr 2002
Posts: 2981 |
Quoting JackAsserWhen the VIC needs to steal cycles for DMA, will the currently running REU-DMA simply be halted and resumed after the VIC-DMA? Will the VIC also stall the REU an additional 3c like it does when stalling the CPU? Afaik, yes. The REU is very BA-shy, it halts as soon as BA goes low, and does not use the 3 possible write-cycles. Then it continues when VIC-DMA is done. Only heard this, though, and have never confirmed it. |
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