A task switcher for the Final Expansion

[Kananga]

There are of course more amazing things going on, but here is another small contribution to the growing software pool for the VIC-20:

A task switcher for the VIC-20 & FE3. Link

(Already announced in the thread "WIP: VIC GUI", but now with more text )

--- README ---
FE3TS allows you to have up to eight virtual environments on your VIC-20 & FE3.
FE3TS-SV is an example for the supervisor written in BASIC that demonstrates
how to use the task switcher.

You can:
* create and reset environments
* switch between them by using the restore key
* save the state of an environment
* load the state of an environment

Everything works fine unless you overwrite the 3K RAM expansion area at $0400-$0FFF.

If the restore handler doesn't work, because the NMI vector was overwritten, just type SYS 1033 to return to the supervisor (environment 0).


Usage:
------

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LOAD"FE3TS.PRG",8,1
NEW
LOAD"FE3TS-SV.PRG",8
RUN

Interface to FE3TS:
-------------------

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SYS 1024

Initialises the environment structures.

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POKE 780, <nr> : SYS 1027

Resets environment <nr>. (<nr> between 0..7)

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POKE 780, <nr> : SYS 1030

Switches to environment <nr>. Before you can switch to an environments other than 0, you have to initialise it with a call to "Reset".

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SYS 1033

Switches to environment 0. (Equivalent to POKE 780, 0 : SYS 1030)

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POKE 780, <nr> : POKE 781, <file> : SYS 1036

Writes environment <nr> to <file>. You have to open a file in write mode before calling this routine and close it afterwards. <file> is the logical file number you chose for your file. You can write more than one environment to one file through successive calls to this routine.

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POKE 780, <nr> : POKE 781, <file> : SYS 1039

Reads environment <nr> from <file>. <file> is the logical file number of a file and must be open for reading.

[Vic20-Ian]

So the VIC now has a kind of unix like virtual console for 8 machines?

If above = true then WOW!

[Kananga]

So the VIC now has a kind of unix like virtual console for 8 machines?

Sorry, but no. It is neither multi-tasking nor multi-user.

You have 8 virtual machines (with one dedicated to be the supervisor), but they don't run simultaneously. If you switch back to the supervisor, all RAM, Video & CPU state is saved and you can
- switch to another machine.
- switch back to were you left.
- save the state to disk and load it again anytime later.
- hit reset (yellow button) to reset the active machine (only).
- (soft) reset the machine from the supervisor.

I have to admit that it works better than I expected, considering that the Vic-20 has no concept of memory protection. Also I do not see a way to reliably save & restore the state of the VIAs. It is just not possible.

Basically, I wanted to make use of the 512K RAM on the FE3 that is mostly idle, which is a shame