CPUWIZ Posted July 26 Share Posted July 26 I am asking, because one of my 7 units will not present RAM there, it leaves the region unmapped. Can't be the only one, so if you do, fix it or your homebrew may not work on all machines! Quote Link to comment Share on other sites More sharing options...
+-^CrossBow^- Posted July 26 Share Posted July 26 2 hours ago, CPUWIZ said: I am asking, because one of my 7 units will not present RAM there, it leaves the region unmapped. Can't be the only one, so if you do, fix it or your homebrew may not work on all machines! What are you using to test the mirroring on the RAM? I believe @RevEng's 7800 utility cartridge has a mirror test as part of the RAM testing routine? Quote Link to comment Share on other sites More sharing options...
CPUWIZ Posted July 26 Author Share Posted July 26 18 minutes ago, -^CrossBow^- said: What are you using to test the mirroring on the RAM? I believe @RevEng's 7800 utility cartridge has a mirror test as part of the RAM testing routine? I mapped my own RAM into that area and wrote my own test and that only works on one motherboard, every other one crashes hard. Quote Link to comment Share on other sites More sharing options...
+-^CrossBow^- Posted July 26 Share Posted July 26 1 minute ago, CPUWIZ said: I mapped my own RAM into that area and wrote my own test and that only works on one motherboard, every other one crashes hard. Interesting, I've yet to see any 7800 cross my path that failed the RAM test routines in the utility cart but then I'm sure it is possible to do some funky stuff to stress it all more. The only real issue with any homebrew I've been a part of, was do to a few Rockwell CPU based 7800s not liking the games and crashing within a few min of playing or exhibiting quite a bit of graphical corruption on the screen (During DLI I think?). In those instances, I've advised my clients to let me replace the CPUs with a different brand. Usually Signetics or NCR when I can. But the RAM I've never found I've had to replace although as you know from a previous posts, there was as lot of different brands and spec RAM used in the 7800 throughout the production cycles with other components changes being done on the fly to work with them. Quote Link to comment Share on other sites More sharing options...
CPUWIZ Posted July 26 Author Share Posted July 26 I don't think it has to do with the RAM at all, it is what selects the individual CS lines on the RAM chips. Usually mirrors exist, because people cut corners on address line detection (to save pins and parts, especially back then). I think this board actually pays proper attention to the region for some reason, I have no time to trace the whole thing but I am sure another one exists. Quote Link to comment Share on other sites More sharing options...
CPUWIZ Posted July 26 Author Share Posted July 26 Basically, the lack of bus contention is what let my RAM work, because the original RAM wasn't chip selected. Quote Link to comment Share on other sites More sharing options...
Eagle Posted July 26 Share Posted July 26 SN cart has mirror ram. https://home.mycloud.com/action/share/1778d186-d16d-4990-8cc2-db827e0f21a2 Quote Link to comment Share on other sites More sharing options...
CPUWIZ Posted July 26 Author Share Posted July 26 6 hours ago, Eagle said: SN cart has mirror ram. https://home.mycloud.com/action/share/1778d186-d16d-4990-8cc2-db827e0f21a2 I think you misunderstood, I am talking about the region of memory below $4000. I have done some crazy RAM bankswitching as well, but the goal is a bigger footprint of RAM. Quote Link to comment Share on other sites More sharing options...
Eagle Posted July 26 Share Posted July 26 Sorry, I thought that you are talking about mirror ram 🤦♂️ Quote Link to comment Share on other sites More sharing options...
CPUWIZ Posted July 28 Author Share Posted July 28 Wow, I am socketing one of my boards and I just came across the weirdest RAM modification. How does this even work? Maybe I am just tired, but pulling WE into a permanent state doesn't make sense to me, maybe the other end of the resistor isn't GND or VCC? I have to look at the trace, maybe this is the board that allows the extra RAM mapping (I forgot which one it is). Quote Link to comment Share on other sites More sharing options...
CPUWIZ Posted July 28 Author Share Posted July 28 Never mind, they only dampen the WE line, not sure why. Quote Link to comment Share on other sites More sharing options...
+batari Posted July 28 Share Posted July 28 I don't think it's normal to be missing the mirrors of $40-$FF/$140-$1FF at $2040-$20FF/$2140-$21FF, and I would suspect a broken console. Quote Link to comment Share on other sites More sharing options...
+-^CrossBow^- Posted July 28 Share Posted July 28 3 hours ago, CPUWIZ said: Never mind, they only dampen the WE line, not sure why. I've seen that factory modification done on many many 7800s. I believe it is present on most that have RAM faster than 150ns in use like the one you've shown that appears to be 100ns speed? It is mostly Sony brand chips I see they have done this too, but I've found it on others as well but it tends to be mostly the Sony RAM that gets this factory modification. I actually desolder the lead from the resistor to the IC leg and apply shrink tubing over it before attaching it back into place. 1 Quote Link to comment Share on other sites More sharing options...
CPUWIZ Posted July 28 Author Share Posted July 28 2 hours ago, batari said: I don't think it's normal to be missing the mirrors of $40-$FF/$140-$1FF at $2040-$20FF/$2140-$21FF, and I would suspect a broken console. I am talking about $2800. Quote Link to comment Share on other sites More sharing options...
Trebor Posted July 28 Share Posted July 28 Per the A7800 source, derived from actual hardware testing and analysis from @RevEng and others: Quote AM_RANGE(0x2000, 0x27ff) AM_RAM AM_SHARE("6116_2") // According to the official Software Guide, the RAM at 0x2000 is // repeatedly mirrored up to 0x3fff, but this is evidently incorrect // because the High Score Cartridge maps ROM at 0x3000-0x3fff // Hardware tests show that only the page at 0x2700 appears at // 0x2800, and only on some hardware (MARIA? motherboard?) revisions, // and even then with inconsistent and unreliable results. The updated Software Guide also denotes the memory map conflict (2800 to 2FFF). Quote Link to comment Share on other sites More sharing options...
CPUWIZ Posted July 28 Author Share Posted July 28 4 hours ago, Trebor said: Per the A7800 source, derived from actual hardware testing and analysis from @RevEng and others: The updated Software Guide also denotes the memory map conflict (2800 to 2FFF). Yes, that is precisely what I am talking about, one of my machines allows $2800-$2FFF to be mapped. 👍 Quote Link to comment Share on other sites More sharing options...
+batari Posted July 29 Share Posted July 29 12 hours ago, CPUWIZ said: I am talking about $2800. Yeah, I believe that old document from 1998 is simply wrong. I've never found anything solid at $2800 on any console. Some versions of Concerto firmware have used this area, and not a single issue has been found with using $2800-$2FFF after boot. I am not sure why your console presents RAM there, but it's possible it's just weakly driven when the chip selects are not active. However, you can't just put RAM there until after boot, as I understand this area is used by the BIOS while some of the upper address lines are zeroed out. 1 Quote Link to comment Share on other sites More sharing options...
CPUWIZ Posted July 29 Author Share Posted July 29 3 hours ago, batari said: Yeah, I believe that old document from 1998 is simply wrong. I've never found anything solid at $2800 on any console. Some versions of Concerto firmware have used this area, and not a single issue has been found with using $2800-$2FFF after boot. I am not sure why your console presents RAM there, but it's possible it's just weakly driven when the chip selects are not active. However, you can't just put RAM there until after boot, as I understand this area is used by the BIOS while some of the upper address lines are zeroed out. Hmm, writing to $2000 is the same as $2800 on several of my RAM tests, maybe I did something wrong back then (it was 10 years ago). And yeah, I know about the BIOS, I screwed myself up with that. Quote Link to comment Share on other sites More sharing options...
PacManPlus Posted August 12 Share Posted August 12 I started reading this thread, saw Mirror Ram and immediately this came to mind: (Sorry for the de-rail) Quote Link to comment Share on other sites More sharing options...
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