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2012-09-21 07:56

Martin Piper

Registered: Nov 2007
Posts: 722

Turbo tape boot loaders

I was playing around with some tape turbo loader stuff recently.
The first boot loader, the first kernal format file that auto starts, has some code in the tape buffer when the filename is displayed. Then there is only one file data block is written to tape instead of the usual second repeated data blocked for the kernal to verify the loaded file data.

It returns control to the kernal a couple of seconds earlier because the $0314 IRQ vector is restored to normal by the loaded data so the "BASIC Input Line and Decode" $0302 vector is hit which contains the boot loader start address.

I was wondering how many turbo loaders used the IRQ vector escape method to trigger an early exit back to program control and only saved one block of tape data?

2012-09-21 16:46

tlr

Registered: Sep 2003
Posts: 1790

I personally haven't seen it but I didn't analyze that many loaders.

You can do this using the break vector ($0328).

I guess most loaders still keep the second repeated block even though they have already started before it is read.

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