MAME: Electron MRB

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Pernod
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MAME: Electron MRB

Post by Pernod » Wed Mar 21, 2018 5:10 pm

How does the Master RAM Board work?

I know it provides an extra 32K shadow RAM, but is it switchable like Master/B+? I'm guessing it's not switchable so under what condition is the original RAM written to for video?

Similarly, under what condition is the original lower 12K accessed?

When the Electron OS 3.00 starts it shows either 64K or TURBO when switch is in either mode, how is the MOS detecting which mode is selected?
- Nigel

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ThomasHarte
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Re: MAME: Electron MRB

Post by ThomasHarte » Thu Mar 22, 2018 2:42 am

I can answer only as far as covered here, which covers behaviour when in shadow mode — most recent PC address (latched upon SYNC) plus the value written to 0xfc7f dictate visibility.

I don't recall offhand how shadow or turbo mode is detected at runtime, if it isn't just a ROM substitution.

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Re: MAME: Electron MRB

Post by Pernod » Thu Mar 22, 2018 4:14 pm

ThomasHarte wrote:I can answer only as far as covered here, which covers behaviour when in shadow mode — most recent PC address (latched upon SYNC) plus the value written to 0xfc7f dictate visibility.
Thanks, actually found that thread around the same time you posted last night. Anyway, both Turbo and Shadow modes are now working in MAME :)
0069.png
0067.png
And StarWord finds the extra free space so must be good.
0065.png
Looking at the Elkulator code in mem.c in Turbo mode it's only using shadow RAM for 0x0000-0x1fff, is this correct or should it be 0x0000-0x2fff?
- Nigel

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Re: MAME: Electron MRB

Post by ThomasHarte » Thu Mar 22, 2018 5:13 pm

Pernod wrote:
ThomasHarte wrote:I can answer only as far as covered here, which covers behaviour when in shadow mode — most recent PC address (latched upon SYNC) plus the value written to 0xfc7f dictate visibility.
Thanks, actually found that thread around the same time you posted last night. Anyway, both Turbo and Shadow modes are now working in MAME :)
So what's the part that my decaying brain couldn't provide — what's the trigger for displaying 'Turbo' rather than '64kb'?
Pernod wrote:Looking at the Elkulator code in mem.c in Turbo mode it's only using shadow RAM for 0x0000-0x1fff, is this correct or should it be 0x0000-0x2fff?
Classic turbo boards accelerate only 8kb, which could be the source of confusion. But I understood the MRB to accelerate the lowest 12kb. I cannot find a concrete reference either way though.

Now that you have MRB support, if you ever find a copy of Stop Press 64 then please be loud about it. I've never managed to track that down.

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Re: MAME: Electron MRB

Post by Pernod » Fri Mar 23, 2018 12:56 am

ThomasHarte wrote:So what's the part that my decaying brain couldn't provide — what's the trigger for displaying 'Turbo' rather than '64kb'?
I've implemented as per Sarah's post viewtopic.php?f=54&t=12242&p=155982#p155638 and the OS 3.00 displays accordingly.
ThomasHarte wrote:Classic turbo boards accelerate only 8kb, which could be the source of confusion. But I understood the MRB to accelerate the lowest 12kb. I cannot find a concrete reference either way though.
That makes sense, why pay for 16Kb if you only need 12Kb, in fact 8Kb would've been most cost effective at the time.
ThomasHarte wrote:Now that you have MRB support, if you ever find a copy of Stop Press 64 then please be loud about it. I've never managed to track that down.
We already have the ROMs, see viewtopic.php?f=4&t=14384&p=192175#p192605. I don't know how to use them though, suspect we may need MIA floppies to go with them. ROMs were in the Slogger haul from viewtopic.php?f=32&t=11795#p148282
- Nigel

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Re: MAME: Electron MRB

Post by ThomasHarte » Fri Mar 23, 2018 1:11 pm

I'm being such a dunce in this thread that I almost hesitate to respond again, but...
Pernod wrote:I've implemented as per Sarah's post viewtopic.php?f=54&t=12242&p=155982#p155638 and the OS 3.00 displays accordingly.
Then I guess it's testing the memory map rather than expecting the switch to be directly readable. Neat, simple.
Pernod wrote:
ThomasHarte wrote:Now that you have MRB support, if you ever find a copy of Stop Press 64 then please be loud about it. I've never managed to track that down.
We already have the ROMs, see viewtopic.php?f=4&t=14384&p=192175#p192605. I don't know how to use them though, suspect we may need MIA floppies to go with them. ROMs were in the Slogger haul from viewtopic.php?f=32&t=11795#p148282
Frustratingly, I think your suspicion should be considered fact: per the E.U.G review, "[t]he package is very easy to use; just insert the system disk and press SHIFT-BREAK."

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Re: MAME: Electron MRB

Post by Pernod » Fri Mar 23, 2018 1:18 pm

ThomasHarte wrote:Frustratingly, I think your suspicion should be considered fact: per the E.U.G review, "[t]he package is very easy to use; just insert the system disk and press SHIFT-BREAK."
There are apparently two versions of Stop Press 64, one requires a board (that needs reverse engineering), and the other is cartridge only which I do support (if it works). The review also states:
The circuit board is hard wired to the Master RAM Board and a new operating system (v3.1) is installed. A cartridge version with or without User port should be available later this year.
so we also need the OS 3.1.
- Nigel

BBC Model B, ATPL Sidewise, Acorn Speech, 2xWatford Floppy Drives, AMX Mouse, Viglen case, BeebZIF, etc.

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