13 Jun
2014
13 Jun
'14
10:52 a.m.
Yes, you want to do it when the disk is first logged in. You can determine
this by checking the low order bit of register E when SELDSK is invoked.
If the bit is clear, the disk is being logged in and id is
safe/appropriate to modify the corresponding DPB as needed.
--Wayne
On Thu, Jun 12, 2014 at 11:36 PM, Eric Smith <spacewar at gmail.com> wrote:
I'm told that some vendors shipped CP/M systems
that would auto-detect
between several disk formats, e.g., 8-inch single density vs double
density, but I've never used one. Obviously the BIOS would change the
values in the disk parameter block. At what point is it safe for the BIOS
to do that? Obviously you wouldn't want to do format detection every time
the BIOS SELDSK function is called, but is it reasonable to do it whenever
READ or WRITER are called after a SELDSK of a changed drive number? Or is
there a way the BIOS can figure out specifically when the BDOS is trying to
log in a new disk?