********************************************************************* * * * AMICOM'S A3000 MMU PATCH VERSION 1.11 (1990-09-18) * * * ********************************************************************* ChipCache V1.11 Description --------------------------------------------------------------------- This is a small tool that can improve the performance of certain A3000 configurations by turning on Instruction Cache in Chip-Memory. Furthermore, it allows you to make use of an additional 200kB of Fast Memory when running under Kickstart 1.3. It is rather hacky and will probably not work on future releases of the A3000 Operating System. To prevent crashes, a number of checks are done. First version 1990-08-15 Updates: V1.09a (1990-09-17): 2nd issue of bad -RESET bug fixed by flushing data cache after every switch. Seems that 68030 can create shit entries in datacache. V1.10 (1990-09-18): AmigaDOS 2.x proper cache control implemented. Former versions were unable to change cache status in 2.x V1.11 (1990-09-19): Showmem routine built in. ChipCache V1.11 History and About --------------------------------------------------------------------- Let me first explain how I came to the idea for this tool. Of course one of the first things I did with my new A3000 was to check out some graphics software to see the speed-improvements. Thereby I made an interesting observation: A demo that did not work on the A2620 unless you turned-off Instruction Cache worked perfectly with the Instruction Cache turned on! I started to investigate on that until I finally came across a line of text in the 68030 manual that says: 'The CI bit will disable both caches in the corresponding pages'. The problem is the following: you MUST disable the Data Cache in all locations where other devices than the CPU can alter memory. Imagine a word of data being read from memory by the CPU. This word is stored in the Data Cache. The next time the program reads the same memory location, the word is fetched from Data Cache instead from memory, to increase speed. However, if the same memory location has been written to by disk DMA for example, then the value in the cache is not valid and incorrect data is being used by the processor. Treating of such memory regions is done by means of either the MMU translation table (which in the A3000 is also used to map the Kickstart into the correct place), or by the memory controlling hardware. Hardware Cache disable is done on a cycle-by-cycle basis through a pin on the 68030. Software Cache disable uses a special bit named Cache Inhibit in the MMU tree structure. On the 68020/68851, this would only disable Data Cache. On the 68030, this same bit also disables Instruction Cache. Why this is, I cannot tell and I'm afraid there is no sense in it. Under no circumstances, neither graphics DMA data, nor hardware registers will ever be used as program (Assembler instructions). [ There is one big exception to that: Harddisk DMA. BUT: that problem is resolved by a different means: The Instruction Cache is flushed after every harddisk DMA load. So that point can be left out in the discussion. ] With a standard A3000 using the disk-Kickstart you have about 300Kb of FAST memory after boot-up. Therefore you will very soon end up without FAST mem and code gets loaded into CHIP memory, causing heavy performane degradation. This degradation results from two sources: - The Chip memory clock is only 7.16 MHz compared to 25Mhz in FAST memory. - There is no Instruction Cache in Chip Memory The latter can now be fixed using ChipCache at the cost of complete renounce of the Data Cache. Note that this is by no means a general improvement to the A3000. It does in fact REDUCE the performance of a well-equiped A3000 that has lots of FAST memory, because it requires disabling the Data Cache. ChipCache V1.11 Instructions --------------------------------------------------------------------- ChipCache lets you - help the no-Cache-in-Chipmemory problem - find out how much Kickstart-memory is unused and can be used otherwise - remove the write protection of that memory, allowing write access to the system MMU translation table * The CHIPMEMORY CACHE FUNCTION is completely undangerous and so you may enter without risk: ChipCache which will present you an overview of the former and the new system status. Two parameters are changed: The Chipmemory Cache is turned on and the Data Cache is turned off (see 'About'). The Chipmemory Cache function is of equal usefulness in both Kickstart / AmigaDOS 1.3 and 2.0 * If you want to go BACK TO THE INITIAL STATE, just enter ChipCache -RESET You need not use capital letters for options and you may take advantage of the abbreviations stated after the options names presented by ChipCache ? * Extensive experimenting showed me that despite the considerations about Data Cache in Chip Memory, the machine may actually work ok. THIS DOES NOT MEAN THAT I GUARANTEE THAT IT WORKS! To allow you to experiment for yourself, I built-in option DATA. USE IT AT YOUR OWN RISK! System crashs can cause 'Key already set' problems! It is quite safe to use it with low-level (non-multitasking) software like Starglider and other games. Here, a speed increase can be stated. To enable both Chipmemory and Data Cache enter ChipCache -DATA * Since the Kickstart 1.3 uses only about 270kB of the 512kB that are allocated for it, and we are very short of Fast Memory on the standard A3000, I came to the idea to use the free space as system memory. Unfortunately, this region is write protected by MMU code that is set-up by the boot-rom. Therefore, I built a tool that removes this write protection and fitted it into ChipCache, too. To take advantage of this also, you need first to find out where exactly that usable memory is located. To do so, enter ChipCache -SHOWMEM This will most probably give you the answer: Addable memory from $07FC5000 to $07FFFFFF. Note that this inquiry cannot be repeated after you used that memory as system memory. It works only as long as this memory has never been touched. Then, you need to remove the writeprotection by entering ChipCache -NOWPRO As you can see now, the status of the write protection has changed to inactive. Now you may add that memory to the system using the AddMem tool. Enter AddMem $7fc5000 $7ffffff CAUTION: - Attempting to AddMem to a region that does not contain usable memory will instantly result in a crash. - From now on, you must pay attention to NOT use option RESET since this would reinstall the writeprotection and therefore crash the machine. Note: To overcome the problem that option RESET may not be used while the additional memory is being used, option NOCHIPCACHE lets you remove just the Chipmemory Cache, without touching the writeprotection. * The memory part that is usually write-protected contains - the new libraries, devices and resources the A3000 Kick '1.3' needs - the system MMU translation table Be careful not to overwrite any of these! If you want to look at the translation table, use CINFO (by me!) to locate it. If know what you're doing, you can change the translation table after removing the write-protection! Note also that the translation table is reset-proof, so you end up in a reboot-crash-loop if you trash it! Have Fun! ChipCache V1.11 Options --------------------------------------------------------------------- Usage: ChipCache [-DATA=D] [-NOWPRO=NP] [-RESET=R] [-NOCHIPCACHE=NC] [-SHOWMEM=S] -DATA = D This option causes the Data Cache not to be turned off. The state your machine goes into using this option is not guaranteed to be stable. Use this option AT YOUR OWN RISK and be careful! The best thing is to start a low-level application immediately after activating ChipCache with Data Cache. -RESET = R This option resets the chipmemory Cache (inhibts it) to normal mode. It will also turn on the Data Cache and set the write protection of the translation table memory. CAUTION: You must not use RESET when you have added memory because this memory will then be write-protected! -NOWPRO = NP This option causes the write protection of the top 256kb of FAST RAM (from $07fc0000 to $08000000) to be removed. You are able then to alter the translation table, or use some free memory for your own purposes. -SHOWMEM = S This option will tell you the address range (if any) in the top FAST memory region that is unused and can be gained using AddMem. NOTE: This option will only work if you did not use the extra memory region before, because it simply scans for the beginning of the region containing only zeros. -NOCHIPCACHE = NC This option reverts the chipcache function. Chipmemory Cache will be turned off. ChipCache V1.11 Error messages --------------------------------------------------------------------- If ChipCache fails because either - you gave invalid options / parameters - there was an internal problem (e.g. incompatible OS version) - you used it on a system it does not apply to then it returns an error code of 20. You may use this for script files like the Add200k tool supplied with ChipCache. Here is a list of all ChipCache error messages: *** This is not an A3000! *** Cannot recognize the A3000 translation table! Either you have a different A3000 Boot-ROM than I, or you are cheating, using ChipCache on a GVP-Board or so. *** The translation table is somehow strange. Hmmm... strange! *** Translation table outside of expected memory page! ROM OS version conflict. Please contact me. *** Sorry, unable to handle the 68040! I have not yet had the pleasure to try it out. *** Input line too long! *** Got unexpected argument. Check for '-' before options. *** Option RESET must be used alone!