Nula issues

[SamSkivington]

Hello. Sorry. Me again.

1. I can't disable Nula once enabled in v2.2 or https://github.com/stardot/b-em/releases/tag/m5000-filt
2. If I do something to adjust palettes with Nula and then switch model the previous Nula changes persist

These should probably be separate issues, right?

For 1, it 'thinks' it's disabled but doesn't have any effect and after a restart of b-em Nula is enabled again

[SteveFosdick]

Sorry it has taken me so long to see this.

Yes, I think there are two different things here and, assuming you are talking about the NuLA item in the Settings->Video, maybe this doesn't do what you are expecting it to. It doesn't either stop a palette already programmed into the NuLA from being used or reset the palette to the default. Unticking it causes the whole of the address space allocated to the Video ULA to address only the two registers in the original Video ULA. This would enable software that relies on the partial address decoding used to work correctly and also avoids NuLA being upset by spurious writes.

There is an command in the NuLA support from, *VNDISABLE, which does a similar thing which it does by writing command #5 to the NuLA control register. The documentation, page 15 of the NuLA user guide (version 1.3) does say this disables NuLA features but in B-Em it only affects addressing as that was my understanding at the time NuLA was added to B-Em.

You're right, this is not saved to the config file and re-loaded when b-em is re-started. That was to mimic a real NuLA which always starts with NuLA enabled. On a real NuLA, disabling it lasts until the next power cycle, though B-Em allows to re-enable it via this menu setting.

The other issue, about when the NuLA palette gets reset, is tried up with the fact that B-Em has not been completely consistent about whether the hard reset (File->Hard Reset) or a change of module is exactly equivalent to a power cycle. A real NuLA is quite resistant to the palette being reset - it doesn't reset on either a Break or Ctrl-Break. But I can see an argument that hard reset should be roughly equivalent to turning off and on again and thus should reset the NuLA pallette.

In the meantime, if you need to reset the palette, *VNRESET in the NuLA support ROM will do this or you can write command code 4 to the NuLA control register so, with BASIC in the I/O processor (no tube): ?&FE22=4.