Re: Question on ProDOS SmartPort drive remapping

[glen herrmannsfeldt <gah@ugcs.caltech.edu>]

Peter Watson wrote:

(snip)

> The problem was that also by convention a program's return code should be 
> loaded into register 15, but in IEFBR14 it still contained the value on 
> entry, which just happens to be the program's entry point address! So the 
> do-nothing program was always reported as ending with an non-zero error if 
> anything checked the return code! (The fix doubled the size of the program 
> to four bytes! Register 15 was cleared before returning.)

There was a long discussion on this once.  Only the low 12 bits are
used for the return code.  It has been suggested that on early OS/360
programs were loaded on a 4K byte boundary, so the return code was zero.

With protection on 2K boundaries, it would make some sense, but it
was never confirmed.

-- glen