Posted By
Plus4fan
on 2010-08-14
04:48:32
|  Re: HER turbo & autostart
The theory of operation of auto starting / auto turbos always interested me, but I never had a chance to understand it (in 1987-1990 period).
Now I have analyzed it:
1. On the initial stage (after load + play) the tape buffer is filled with the:
$333 - load start address: $314, the IRQ vector
$336 - load end address: $336, only 2 Bytes are loaded
$338 - file name (16 Bytes)
$348 - turbo loader code
2. After the 2 Bytes are loaded at $314 ($48 $03), the IRQ calls the loader code at $348.
The 1st stage loader loads the 2nd part of the loader $200. The 1st stage loader calls the 2nd stage loader (jmp $200) at $390.
3. The 2nd stage loader loads the turbo saved program to the final address (> $1000) and starts it with direct jump at $236 (or with JSR to $8xxx if it has to be started with RUN command).
Some HER versions use the $700 area for the stage 2 loader.
This is what I always wanted to know about HER. :)
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