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Author Topic: mbed emulating a ROM cartridge  (Read 14203 times)
Janzl
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« Reply #45 on: March 02, 2012, 10:11:15 AM »

Shit! Now I have to go to Apeldoorn.
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gertk
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« Reply #46 on: March 02, 2012, 12:56:54 PM »

Do not worry, only the proto is going to Apeldoorn but maybe we can discuss some small production batch.
Rene are you going to Apeldoorn too?
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Seob
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« Reply #47 on: March 02, 2012, 02:51:28 PM »

Shit! Now I have to go to Apeldoorn.
I see you in Apeldoorn then. Will be there between 10.00 and 14.00.
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manopac
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« Reply #48 on: March 02, 2012, 08:37:36 PM »

btw: any chance to also include C7420 emulation in the cartridge?
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gertk
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« Reply #49 on: March 03, 2012, 12:06:59 AM »

btw: any chance to also include C7420 emulation in the cartridge?

It is on the list along with Chess. The code is already available from my earlier C7420 emulator. Basic program storage will be on SD card of course. The software emulation of the latches needs some rework.

By using the LPCxpresso I got even more cycles available since I could connect the address and data bus on adjacent port pins instead of having to combine them from three different IO ports.
From every 2.5 usec cycle of the 8048 CPU I have about 1.5 usec available for the mbed/lpc so it leaves enough time to do Z80 emulation. Whenever the 8048 CPU is reading from internal rom the  mbed/lpc is running full speed.
For now I will concentrate on getting the reset circuit ready for Apeldoorn, menu program (Videopac code) is a very early rough version, Voice emulation works for 95% (the 5% being an odd timing problem resulting in sounds being buffered and played back too late, something to do with the reset bit) but all of this is software and not hardware.
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Seob
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« Reply #50 on: March 04, 2012, 11:11:04 PM »

Gertk showed his cart on one of the few running systems in the place, due to a shortage on power outlets. I was very impressed by the demo. Amazing what one can build and squeeze inside that tiny videopac cartridge, and still have a bit of room for spare.
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« Reply #51 on: March 06, 2012, 10:18:18 PM »

Another small succes:

I could not get the Voice timing quite right and there was no way I could use another interrupt without crashing the rom emulator.
But then I found another neat feature of the mbed/LPC's CPU: the System Timer. It is basically a free running counter with a reload option on crossing zero. Normally it is used to create a 'System Tick' for multitasking purposes but I used it to setup a 10 kHz reference for the audio sample output. By simply waiting until the reload flag gets set I have a strict timing offset for the samples without using interrupts.

Now even Crazy Chase sounds OK (Janzl knows how it sounded at the demo... It was slooooowwww... )
Nimble Numbers and Acrobats sound a lot better too..
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Seob
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« Reply #52 on: March 06, 2012, 11:16:17 PM »

And no more missing sounds when playing Smithereens?
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« Reply #53 on: March 07, 2012, 07:26:13 PM »

And no more missing sounds when playing Smithereens?

Naah, almost  Smiley Still don't know what is going on there exactly, if I change just some non-trivial things in the testloop of the reset bit it changes behavior already so my guess is that the command and reset bit values are getting cached or optimized in some way.
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« Reply #54 on: March 27, 2012, 09:46:14 PM »

Another 'small' improvement:

The LPCxpresso has a single LED onboard but it is connected to P0_22 and that was a pin I used to read the Videopac's bankswitching output P11.

On the G7000 and G7200 it resulted in some visual instability and on screen menu corruption. Seems the LED (with 2k resistor) pulls the line down to much and it sometimes registers as '0' when it should be '1'. By shuffling some pins around (luckily the LPCxpresso has some left) this problem is now gone too. Another step in the right direction.
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« Reply #55 on: December 30, 2014, 02:39:30 PM »

What is the status of this project gertk?
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« Reply #56 on: December 30, 2014, 07:00:19 PM »

The status is 'dormant'  Smiley Lately I got a new small ARM CPU to play with and will see if it is up to the job to be used in the emulator (it is the STM32F103 btw) The chip is cheap and even when presoldered to a tiny board it is just a few dollars.

Biggest problem is time and too much things on my mind and hands...

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