Well, unexpectedly I received responses from both programmers on the same day, and both were supportive and helpful which is great!
There was some confusion about which revision of the game ROMs I should be using as my starting point, but that's now sorted. Fortuitously (although not critical to my needs) both the reverse-engineering effort and the port/emulator are based on the same revision!
After the feedback I received I've officially decided on the next Coco3 port.
But back to Space Invaders for now...
Monday, 20 February 2017
Thursday, 16 February 2017
Ping timed out.
Just a quick note to say that I am still working on Space Invaders. Slow going as I'm still coming up to speed with how it all works again, but at least now the shields are in approximate position, albeit yet to be rotated.
Interestingly a thread in an Apple II programming group led to a brief discussion on Apple Invader. Now that was an impressive home conversion back in the day, and would have been a little easier to port to the Coco3 than the arcade original... but not quite as cool?
Still been thinking about the next Coco3 project. It would be fair to say that this game is an unlikely candidate for a Coco3 port due mainly to the hardware used, and that's a big part of the attraction for me. Surprisingly it has actually been ported to other 8-bit machines! I've approached two different programmers that have worked on either reverse-engineering or porting the original, but neither have deigned to respond thus far.
Never mind, I think I have the technical details worked out. Just would have been nice to compare notes and perhaps get some insight into the performance I could expect on the Coco3 without having to employ further trickery...
Interestingly a thread in an Apple II programming group led to a brief discussion on Apple Invader. Now that was an impressive home conversion back in the day, and would have been a little easier to port to the Coco3 than the arcade original... but not quite as cool?
Still been thinking about the next Coco3 project. It would be fair to say that this game is an unlikely candidate for a Coco3 port due mainly to the hardware used, and that's a big part of the attraction for me. Surprisingly it has actually been ported to other 8-bit machines! I've approached two different programmers that have worked on either reverse-engineering or porting the original, but neither have deigned to respond thus far.
Never mind, I think I have the technical details worked out. Just would have been nice to compare notes and perhaps get some insight into the performance I could expect on the Coco3 without having to employ further trickery...
Tuesday, 7 February 2017
The Space (Invaders) - Time Continuum
With Lode Runner and Knight Lore in a holding pattern for very different reasons, as promised I turned my attention back to Space Invaders tonight. It wasn't easy as the temptation is there to start on a new port altogether, but I'm resolved to finishing off the existing ports before starting any more.
[On that note: not-so-good news for Coco fans is that the C port of Lode Runner (Neo Geo plus other platforms) will be next on the list and then finally I intend to return to Donkey Kong on the Neo Geo now that my NeoSD AES should soon be shipped! However I still have at least another two, and possibly more, Coco3 projects in mind that I'm keen to start!]
Nothing terribly exciting to report but tonight I have reverted all my on-the-fly rotation code and gone back to 12th May 2016. Somewhat prophetically, I last backed out these changes on... Friday 13th May 2016! I do, however, need to review some fixes I did subsequently after moving the video RAM base address.
As it stands attract mode runs (with rotated text) and the alien rack is displayed (also rotated) before the game appears to crash with small areas of corruption on the screen. Encouragingly, this is exactly what the SVN log describes!
For latecomers: I should note that (behind the display) the Coco3 port is actually completely finished; you can coin up and play a game on a rotated monitor. What I'm in the process of doing now is modifying the code (and sprite data) to display in the correct orientation on the Coco3. Essentially, I'm (simply) rewriting all the rendering routines. It's a bit more complicated than that, but (hopefully) not terribly so.
No doubt it'll take a bit of time to come up to speed with where I was at and in the process I'll probably remind myself of why I opted for the on-the-fly tack... but ultimately this is unquestionably going to run fast enough (with enough headroom to add sampled sound), and the alternate wasn't looking quite so good.
[On that note: not-so-good news for Coco fans is that the C port of Lode Runner (Neo Geo plus other platforms) will be next on the list and then finally I intend to return to Donkey Kong on the Neo Geo now that my NeoSD AES should soon be shipped! However I still have at least another two, and possibly more, Coco3 projects in mind that I'm keen to start!]
Nothing terribly exciting to report but tonight I have reverted all my on-the-fly rotation code and gone back to 12th May 2016. Somewhat prophetically, I last backed out these changes on... Friday 13th May 2016! I do, however, need to review some fixes I did subsequently after moving the video RAM base address.
As it stands attract mode runs (with rotated text) and the alien rack is displayed (also rotated) before the game appears to crash with small areas of corruption on the screen. Encouragingly, this is exactly what the SVN log describes!
 |
| Attract Mode (crash) |
For latecomers: I should note that (behind the display) the Coco3 port is actually completely finished; you can coin up and play a game on a rotated monitor. What I'm in the process of doing now is modifying the code (and sprite data) to display in the correct orientation on the Coco3. Essentially, I'm (simply) rewriting all the rendering routines. It's a bit more complicated than that, but (hopefully) not terribly so.
No doubt it'll take a bit of time to come up to speed with where I was at and in the process I'll probably remind myself of why I opted for the on-the-fly tack... but ultimately this is unquestionably going to run fast enough (with enough headroom to add sampled sound), and the alternate wasn't looking quite so good.
Sound advice
Recently I've been looking at the Lode Runner sound issue (sound is all-but-muted when you enable the joystick) and last night I managed to solve it.
It took a bit to wrap my head around the correct configuration of the two PIAs for joystick and audio support, further muddied by the fact that the Coco has both 1-bit and 6-bit DAC sound generation. Fortunately I found a rather helpful block diagram that Tim Lindner put together that finally enabled me to visualise how all the bits work together.
I had originally assumed that my joystick sampling was inadvertently muting the sound. What should have tipped me off though was the fact that the sound was still there, just very much lower when joysticks were enabled. It turns out, however, that my problem was that I was not muting the sound; the circuit was mixing the 1-bit sound (which FTR can't be muted at all) with whatever state the joystick sampling left the DAC in and the result was barely audible sound from the game.
Once I muted the (DAC) sound during initialisation,the rather basic beeps and boops that are Lode Runner sound were perfectly audible, joystick or no (new release available on the download page linked to the right).
And since I had used the same routines for Knight Lore, it had the same issue - which has subsequently been fixed.
I have been thinking more about the release of Lode Runner (in particular) in the past week or so. When I first ported it I really wanted it to be a cartridge release; not to make any money but just to have at least one tangible Coco product to my name. My thinking was to create a flash cartridge with Lode Runner on it, that the buyer could also use for any other purpose.
However Jim Brain over at RETRO Innovations recently designed an 8MB Flash Cartridge for the Coco line of computers which also includes (and I may have suggested this) a serial EEPROM and (I definitely didn't suggest this) Orchestra 90 emulation.
Although this product is certainly overkill for Lode Runner, it's also - I feel - too expensive to sell as a game cartridge. I'd also like the Lode Runner cartridge to be housed in one of the new shells recently produced for the Coco, with its own "Lode Runner" label.
At the same time I don't want to re-invent the wheel, so in the last day or so I've had the idea to produce an EPROM-based cartridge with a small CPLD for banking and a small serial EEPROM for high score saves etc. Ideally such a cartridge would accept up to, say, 256KB EPROMs (although 1MB would be better) and would be suitable for my other current and future porting projects. The primary design objective is keeping it simple and cheap.
If that gets off the ground then Knight Lore should follow suit soon after.
Shortly I'll turn my attention back to Space Invaders, and finish off the coding for the hand-rotated version, which should have no trouble running at speed on the Coco3. I hope then to be able to add sampled sound, and I have always intended to release it - with source code - for free. Perhaps there'll even be a cartridge release for people that really want one?
It took a bit to wrap my head around the correct configuration of the two PIAs for joystick and audio support, further muddied by the fact that the Coco has both 1-bit and 6-bit DAC sound generation. Fortunately I found a rather helpful block diagram that Tim Lindner put together that finally enabled me to visualise how all the bits work together.
I had originally assumed that my joystick sampling was inadvertently muting the sound. What should have tipped me off though was the fact that the sound was still there, just very much lower when joysticks were enabled. It turns out, however, that my problem was that I was not muting the sound; the circuit was mixing the 1-bit sound (which FTR can't be muted at all) with whatever state the joystick sampling left the DAC in and the result was barely audible sound from the game.
Once I muted the (DAC) sound during initialisation,the rather basic beeps and boops that are Lode Runner sound were perfectly audible, joystick or no (new release available on the download page linked to the right).
And since I had used the same routines for Knight Lore, it had the same issue - which has subsequently been fixed.
I have been thinking more about the release of Lode Runner (in particular) in the past week or so. When I first ported it I really wanted it to be a cartridge release; not to make any money but just to have at least one tangible Coco product to my name. My thinking was to create a flash cartridge with Lode Runner on it, that the buyer could also use for any other purpose.
However Jim Brain over at RETRO Innovations recently designed an 8MB Flash Cartridge for the Coco line of computers which also includes (and I may have suggested this) a serial EEPROM and (I definitely didn't suggest this) Orchestra 90 emulation.
Although this product is certainly overkill for Lode Runner, it's also - I feel - too expensive to sell as a game cartridge. I'd also like the Lode Runner cartridge to be housed in one of the new shells recently produced for the Coco, with its own "Lode Runner" label.
At the same time I don't want to re-invent the wheel, so in the last day or so I've had the idea to produce an EPROM-based cartridge with a small CPLD for banking and a small serial EEPROM for high score saves etc. Ideally such a cartridge would accept up to, say, 256KB EPROMs (although 1MB would be better) and would be suitable for my other current and future porting projects. The primary design objective is keeping it simple and cheap.
If that gets off the ground then Knight Lore should follow suit soon after.
Shortly I'll turn my attention back to Space Invaders, and finish off the coding for the hand-rotated version, which should have no trouble running at speed on the Coco3. I hope then to be able to add sampled sound, and I have always intended to release it - with source code - for free. Perhaps there'll even be a cartridge release for people that really want one?
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