Re: [Freedos-devel] Problem booting FreeDOS on Book8088 PC-XT laptop

[Ralf Q. <fre...@gm...>]

On 2/9/2024 12:13 PM, Bernd Böckmann via Freedos-devel wrote:
> Hi Ralf,
>
> On 09.02.2024 20:02, Ralf Quint via Freedos-devel wrote:
>> I can't see any reason as to why a data segment on a BIOS call should 
>> be set to any random value.
>
> For example, take this code (copied from FDISK source):
>
> static void Reset_Drive( int drive )
> {
>    union REGPACK r;
>    memset( &r, 0, sizeof( union REGPACK ) );
>    r.h.dl = drive;
>    intr( 0x13, &r );
> }
>
> The REGPACK r contains variables for the (segment) registers. In the 
> above, these are initialized to zero by the memset function. If you 
> leave this out, variable r, and so DS, ES contain random values, 
> because r is on the stack. The values of the structure are loaded into 
> the registers before intr calls the requested interrupt, and the 
> original values are restored before it returns. You may of course 
> initialize the individual structure members explicitly. For example DS 
> with the current value stored in the register. But, like said, the 
> above is like the manual recommends.
>
> Greetings, Bernd 
Thanks Bernd, will check this in a bit. The above is one reason why I 
used to write my own asm routines for BIOS calls. Will test this during 
my lunch break, if I can get 86box emulating this X8088book to work... ;-)

Ralf