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F18a proper way to reset the F18a extended registers

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What is the proper way to reset the F18a extended registers so that they have the same values as after a clean power-up cycle?

 

Reason I'm asking is that if you change extended VDP registers the settings stay active even after down a "BLWP @0".

 

In this particular case I have a crash handler in my assembly program that resets the TI to a defined state.

But obviously I do not know what was set in the F18a extended registers by the calling program before.

Could keep track of any value written to the F18a registers, but with the many extended registers that may get cumbersome.

 

In my last example I turn on position-based attributes, but obviously if I reset the TI, the screen is unreadable. 

I know how to resolve this particular case, but would prefer a generic solution.

 

 

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oh wow, just got that time-warp feeling again. Thanks for pointing out the answer to a question I already asked in 2018 😃

 

 

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Posted (edited)

Note that the palette registers are *not* reset.  They are implemented as a memory, which needs to be addresses one location at a time, and only gets an initial setting when the FPGA loads its bit-stream at power on.  That means, any changes you make to the first 16 palette registers will change the "standard" 16-colors used when the F18A is locked or before the palette-select bits are changed (only possible when the F18A is unlocked).

Edited by matthew180
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This brings up a question.  Sometimes things get messed up, other times I'd simply like to clear PALEA5... without power cycling the TI.  Would it be possible to make a small E/A5 reset program?  

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55 minutes ago, GDMike said:

Could it not be saved prior, just asking.

 

We are used to the 9918 registers mostly being write-only. So we think in our soul that the answer is no... but once the F18A is unlocked, the answer changes to yes.   

 

However, it is less code (if the intent is to dump back to the title screen) to ask the F18A to reset what it can, and then let the console rom do the rest... 

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