Author Topic: Unexpected Plus effect  (Read 599 times)

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Offline ComSoft6128

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Unexpected Plus effect
« on: 19:21, 25 March 21 »
Not a programmer, not a hardware guy, so can anyone explain to me the effect seen at the end of this video?

Small B-Asic demo - 6128 Plus only Irish demo from 1994.



https://www.youtube.com/watch?v=5wFpgyjGJDI


Links:

https://www.cpc-power.com/index.php?page=detail&num=11651

https://www.cpc-power.com/index.php?page=staff&lenom=Paul%20GARGAN

https://www.cpcwiki.eu/index.php/Amstrad_User


Not emulated - original hardware and software


Please note that  the aspect ratio for this YouTube video is 16:9 but the CPC monitor
has an aspect ratio of 4:3 so you may wish to adjust your viewing device accordingly.

« Last Edit: 19:31, 25 March 21 by ComSoft6128 »

Offline eto

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Re: Unexpected Plus effect
« Reply #1 on: 20:25, 25 March 21 »
What do you mean?

Offline ComSoft6128

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Re: Unexpected Plus effect
« Reply #2 on: 20:38, 25 March 21 »
"CPC PLUS" is still shown on the screen/overlays the screen display after a soft reset or when the DES Rom is launched - in fact the only way to remove it is to switch off the Plus. I've never seen that before.

Offline Ygdrazil

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Re: Unexpected Plus effect
« Reply #3 on: 20:41, 25 March 21 »

Hi There


Do you mean the CPC PLUS sprites still being displayed on the screen!?


The demo does not clean up after it terminates


Plus features are still enabled by the ASIC so sprites still i ASIC memory..


I think!


/Ygdrazil

Not a programmer, not a hardware guy, so can anyone explain to me the effect seen at the end of this video?

Small B-Asic demo - 6128 Plus only Irish demo from 1994.



https://www.youtube.com/watch?v=5wFpgyjGJDI


Links:

https://www.cpc-power.com/index.php?page=detail&num=11651

https://www.cpc-power.com/index.php?page=staff&lenom=Paul%20GARGAN

https://www.cpcwiki.eu/index.php/Amstrad_User


Not emulated - original hardware and software


Please note that  the aspect ratio for this YouTube video is 16:9 but the CPC monitor
has an aspect ratio of 4:3 so you may wish to adjust your viewing device accordingly.



Offline ComSoft6128

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Re: Unexpected Plus effect
« Reply #4 on: 20:44, 25 March 21 »
Yes the text/sprites are still being displayed but a soft reset doesn't clear them - I thought reset cleared the memory?

Offline Sykobee (Briggsy)

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Re: Unexpected Plus effect
« Reply #5 on: 11:40, 26 March 21 »
Sprite memory is separate, on the ASIC.


As I don't think they changed the firmware from the original CPC, so the clean up of the sprites and their registers is not happening.

Offline ComSoft6128

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Re: Unexpected Plus effect
« Reply #6 on: 19:04, 27 March 21 »
Thanks for the replies/info.


I didn't know the ASIC chip contained memory - 1K/2K or a few bytes?
« Last Edit: 19:11, 27 March 21 by ComSoft6128 »

Offline eto

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Re: Unexpected Plus effect
« Reply #7 on: 19:14, 27 March 21 »
Thanks for the replies/info.


I didn't know the ASIC chip contained memory - 1K/2K or a few bytes?


Probably 4K (16 sprites, 256 Bytes each.)

Offline Skunkfish

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Re: Unexpected Plus effect
« Reply #8 on: 13:14, 28 March 21 »
Since Plus software was intended to be on cartridge and a soft reset not possible (or if it was, it would boot back into the game), they probably though there was no need to clear the ASIC memory on a soft reset...
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Offline Animalgril987

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Re: Unexpected Plus effect
« Reply #9 on: 19:27, 28 March 21 »
The ASIC memory is 16k, and is paged into 0x4000 to 0x7fff in the plus memory map when unlocked and then activated.
 It not only contains sprite colour information, but also X and y coordinates for each sprite, sprite magnification factor, colour palette, DMA channel data, analogue controller data and more.

Offline roudoudou

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Re: Unexpected Plus effect
« Reply #10 on: 19:36, 28 March 21 »
As I don't think they changed the firmware from the original CPC, so the clean up of the sprites and their registers is not happening.
mostly because to clean-up Asic, you need to unlock it first and Amstrad did not want to unlock full features at boot => YOU MUST PAY :D
use RASM, the best assembler ever made :p

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Offline Animalgril987

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Re: Unexpected Plus effect
« Reply #11 on: 19:50, 28 March 21 »
I believe the unlock sequence is on the Wiki... :D

Offline ComSoft6128

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Re: Unexpected Plus effect
« Reply #12 on: 20:12, 28 March 21 »
The ASIC memory is 16k, and is paged into 0x4000 to 0x7fff in the plus memory map when unlocked and then activated.
 It not only contains sprite colour information, but also X and y coordinates for each sprite, sprite magnification factor, colour palette, DMA channel data, analogue controller data and more.


So just to confirm; this is an extra 16K is on top of the 128K on the 6128 Plus giving a total of 144K?

Offline roudoudou

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Re: Unexpected Plus effect
« Reply #13 on: 20:53, 28 March 21 »

So just to confirm; this is an extra 16K is on top of the 128K on the 6128 Plus giving a total of 144K?
It's not exactly memory, it's a mapping to Asic

there is 4096 half-byte for sprites (only lower nibbles are stored/readable) and a few registers (80 bytes for sprites on a 128 bytes area and a bunch of bytes for INT and DMA)
also some adresses are mirrored in the 16K area
this mapping is done in the #4000-#7FFF area so when Asic is mapped, you cannot access RAM below, you must disable mapping
use RASM, the best assembler ever made :p

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Offline Animalgril987

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Re: Unexpected Plus effect
« Reply #14 on: 00:07, 29 March 21 »
Yes, it's as @roudoudou says, I didn't explain too clearly.