Sorry about that message yesterday (title: 'Hoi Sean'), the dutch version was not
intended
for the mailinglist.
My current problem with NLMSX:
I am looking for more information about bit 0 of status register#1. (FH bit)
There are a number of demos/magazines that are using this bit to detect a line
interrupt
by just polling for it while the interrupts are disabled. And this happens even
when the interrupt it self is not switched on, the corresponding interrupt enable bit
is '0'.
I did manage to get those demos/magazines to work, but some of them don't work with the
same implementation. These demos/magazines are:
- Sunrise Special #1, #2, #3
- Sunrise Magazine #8
I would like to know how bit 0 of status register#1 works and specifically what
the conditions are for it to be set to '1'.
This specific bit also works together with register#19 (interrupt line register).
The following bits are also involved:
reg#0, bit 5, Interrupt Enable 2 (also used for lightpen)
reg#0, bit 4, Horizontal scanning line, Interrupt Enable 1
reg#1, bit 5, Horizontal scanning line, Interrupt Enable 0
If someone has more specific info then I could really use it and a lot of emulator
programmers could use it to, because these demos/magazines also 'hang' on
many other emulators.
Interrupt acknowledgement:
One thing that I do know is that if an interrupt is not acknowledged in time,
it will simply disappear. This is something that I still have to implement in
NLMSX.
This means that if bit 7 of status register#0 is read, while Z80 interrupts
are disabled (DI), that the 50/60hz interrupt from the VDP will not be executed.
Bit 7 will be set but the interrupt call itself will not be executed.
This probably is also the case for the line interrupt mechanism.
The people that wrote these demos/magazines must have known a lot of these
inner workings of the VDP that are really usefull to emulator programmers.
Frits
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