Loading routine "cores"
This page documents the "core" of the loading routine used in the various turboloaders: the part of the loader which actually finds an edge from the tape.
The basis for every loading routine out there, this is the one found in the Spectrum ROM (at 05ED). The
LD-SAMPLE name is taken from Logan and O'Hara's The Complete Spectrum ROM Disassembly.
LD-SAMPLE INC B RET Z LD A,7F IN A,(FE) RRA RET NC XOR C AND 20 JR Z,LD-SAMPLE
The names given to each of these loading routines are not meant to imply that loaders was the first to use the specific loading loop; it is the most common usage of the loading loop, or just the first place that it was seen by the authors of this page.
LD-SAMPLE INC B RET Z LD A,7F IN A,(FE) RRA XOR C AND 20 JR Z,LD-SAMPLE
This is essentially identical to the ROM loader, but just without the
RET NC which aborts if space is pressed during the ROM loading routine.
LD-SAMPLE INC B JR NZ,LD-SAMPLE2 JP <somewhere else> LD-SAMPLE2 IN A,(FE) RRA RET Z XOR C AND 20 JR Z,LD-SAMPLE
This again isn't that different from the ROM loader; the minor changes are:
- Inverting the "no edge found" condition
- Using a
JPif an edge is not found rather than a
- Not setting the high byte of the
IN- this isn't critical as it affects only which keyboard half-rows are scanned
- Replacing the RET NC with a RET Z. I think this makes it essentially a no-op unless lots of keys are pressed at once.
LD-SAMPLE INC B JR NZ,LD-SAMPLE2 RET LD-SAMPLE2 IN A,(FE) RRA RET Z XOR C AND 20 JR Z,LD-SAMPLE
This actually makes the Alkatraz routine closer to the original ROM code as it now uses a
RET to exit in the "no edge found" case.
LD-SAMPLE INC B RET Z LD A,7F IN A,(FE) RRA NOP XOR C AND 20 JR Z,LD-SAMPLE
This is just the ROM routine, but with the "space pressed" check explicitly replaced with a
LD-SAMPLE INC B RET Z LD A,7F IN A,(FE) RRA AND A XOR C AND 20 JR Z,LD-SAMPLE
Another very close variant on the ROM loader, this time replacing the
RET NC with the