the cpc supports external interrupts. But to do this the interrupt needs to remain active until it is manually reset (e.g. with out instruction) - or at a minimum have some way to know the source of the interrupt so it can be handled correctly.
the firmware interrupt handler re-enables interrupts, and if the interrupt is still active it assumes that it comes from an external interrupt and executes &003b.
&003b should be patched with the code to disable the external interrupt.
the raster interrupts are cleared manually.
so how can I test this on a normal cpc?
I think it can be done on the cpc+ already with dma interrupts. (Yes looking at the docs this is possible providing the auto-clear of dma interrupts is disabled).
Is there other hardware that used the external interrupt feature?
And don't forget the NMI at &0066 ;-)
Well, what's about the MF-II, doesn't it use the interrupt feature??? Don't remember it exactly.
There was the Z80-STI expansion card from Schneider. By soldering one line on the board, the interrupts have been established. And since they can be programmed, it was a nice toy ;-)
Quote from: TFM/FS on 19:28, 23 June 10
And don't forget the NMI at &0066 ;-)
Well, what's about the MF-II, doesn't it use the interrupt feature??? Don't remember it exactly.
There was the Z80-STI expansion card from Schneider. By soldering one line on the board, the interrupts have been established. And since they can be programmed, it was a nice toy ;-)
I already know about the NMI and quite a lot of hardware uses it.
Multiface-II uses NMI too.
I was more interested in the maskable interrupts from a source outside CPC and the Z80-STI you describe is exactly what I was wanting. Thanks for the info. :)
Thanks TFM :)
There was a loooong time ago an ECB bus project for the CPC. For this ECB bus they have been able to use the so called daisy chain interrupt handling. Quite impressive :-)
I still have three ECB cards which are interrupt capable, one is a fast 38000 RS232 SIO, the others are a SRAM and a EPROM-disc. They were implemented in CP/M.
If you're interrested, then I can try to find informations about it. But this stuff is 25 years old and I don't remember exactly where to start to search...