Subject: Re: [stella] Dumping ROM images From: "Russell Babylon" <rbabylon@xxxxxxxxxxxx> Date: Sun, 13 Mar 2005 11:37:11 -0500 |
OW! OW! stop twisting my arm. I see your point. When I dumped these I tried them out on PCAE and they worked so I didn't think any more about it. Things like this just make the Atari scene more interesting don't you think? :) ----- Original Message ----- From: "Eckhard Stolberg" <Eckhard_Stolberg@xxxxxx> To: <stella@xxxxxxxxxxxxxxxxxx> Sent: Sunday, March 13, 2005 5:13 AM Subject: Re: [stella] Dumping ROM images > > It will work with bank switch games at least for the 'simple' bank > > switching > > schemes. As I said in my original message, and you alluded to below, I > > dumped an 8K game. I did not mention that I had some LEDs hooked to the > > data lines so I could literally see what data was being accessed in the > > ROM > > and I had a pot for the timing resistor on the 555. I would set the pot > > to > > a high resistance so it was clocking at a verrrry slow speed. Sometimes > > the > > ROM would power up in bank one and sometimes in bank two. I read each > > bank > > out separately and then made a quess as to which one was bank one and > > concatenanted the second file to the first. I believe the data after the > > hot spots in the ROM was the same for both banks, even if it wasn't you > > could manually edit the few remaining bytes if need be. Thinking about it > > the vectors after the hot spot would have to be the same, at least for the > > start up address, if the ROM was to power up consistently. As I said > > originally this was a very simple method that required a fair amount of > > knowlege as to the nature of the ROMs and their data structure. It was > > not > > a plug and chug. > > OK, this would allow you to read the major part of both banks. > But you still would have a problem with reading the system vectors > for the first bank, because if you read all addresses from $1000 > to $1fff, you are always accessing $1ff9 before you are are reading > the system vectors from $1ffa to $1fff. Therefore the cart logic > would always switch to the second bank before you can read these > addresses. If you could start the reading at $1ffa and have the > addresses wrap around to $1000 at $1fff, your method might work. > > Most games actually have different system vectors in both banks. > They only have a initializing routine in one bank. In the other > bank they only have a small routine that will switch into the first > bank and jump to the real initializing routine there. > > Of course you could disassemble the code for the first bank in an > 8K game with F8 bankswitching, and try to find the entrance point > for the system vectors. But apparanetly someone didn't do that > for the two games you mentioned. ;-) And if a game used the > unneeded IRQ and BRK vectors for small data tables, you would have > a hard time guessing the correct values. > > I don't know if these two ROMs were the ones you dumped, but > several people did send these two binaries to us because they > didn't work with older versions of z26. We found out that they > didn't work because the system vectors in the first bank (we > started all bankswitched games in the first bank) were the same > as the ones in the second bank, which pointed to bad routines > in the first bank. We figured it might be better to special case > these two games with their own bankswitching, because it's > difficult to replace games that are already in circulation, and > there might be other games with the same problem. But so far > Moonsweeper and Sir Lancelot were the only games that people > complained about because of this. ;-) > > > Ciao, Eckhard Stolberg > > > Archives (includes files) at http://www.biglist.com/lists/stella/archives/ > Unsub & more at http://stella.biglist.com > > Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://stella.biglist.com
Current Thread |
---|
|
<- Previous | Index | Next -> |
---|---|---|
Re: [stella] Dumping ROM images, Eckhard Stolberg | Thread | Re: [stella] Dumping ROM images, Russell Babylon |
Re: [stella] Dumping ROM images, Eckhard Stolberg | Date | Re: [stella] Dumping ROM images, Russell Babylon |
Month |