[Note that I did a copy&paste from the list archives because the mail address I am subscribed to this list isn't working properly atm. I switched to another, but this means I couldn't reply to the original posting and so message threading is broken. Sorry.]
Hi,
Show quoted text 20 lines
under GO32V2 i want to call BIOS PnP function with entry point
db $FF,$1E; dw PnP_EntryPoint
or
call DWord ptr [PnP_EntryPoint]
but always i got error "SIGSEGV - segmentation violation".
PnP_EntryPoint (type pointer) is normally somewhere in BIOS area at
F000:xxxxh.
In PnP specification i found this:
"If this function is called from protected mode the caller must
create a data segment descriptor using the 16-bit Protected Mode data
segment base address specified in the Plug and Play Installation Check
data structure, a limit of 64k, and the descriptor must be readable and
writable."
But i don't know how can i do that
-> "make a readable and writable data segment descriptor".
Probably the easiest way to accomplish that (at least worth a try) is using a method provided by the DPMI server which allows you to call a real mode procedure directly. The only problem is that the GO32 function does not include this call, so you have to use a more complete DPMI interface I did long ago (uploaded at http://members.yline.com/~tom_at_work/dpmidist.zip , for the example programs you may need another one of my units, called MEMORY, grab a copy at
http://members.yline.com/~tom_at_work/memorydist.zip). See the included documentation for dpmi_call_rm_procedure_with_retf_frame and the dcall16.pas and call16.pas example programs which are included. They show how to call a real mode procedure and pass real mode parameters (e.g. buffer addresses) to those.
Btw, the DPMI zip also includes a good DPMI specification =) if you're interested and/or have more detailed questions about it.
If you want to try the way described in the PnP description, have a look at the dpmi_segment_to_descriptor() method which is exactly suited for this purpose (again, see the docs for details). You simply have to provide a base address and it returns you a selector to real mode memory with a limit of 64k. The short example program for this method is called vgasel.pas. (Note that the go32 provides this call too, and there *should* be a similar example program around*).
Then you probably have to pass this selector somehow to the PnP subsystem, but don't ask me how...
* Eg. somewhere lost in the examples directory of the fpc distro. At least there were in some 0.99.x distro... ;-)
And the second problem is how can i make a pointer
"PnP_EntryPoint" to this real memory area.
You can read/write this real mode data by first creating a selector/descriptor to this memory area and use the seg_* methods.
Descriptor creation process:
- use dpmi_allocate_ldt_descriptors
- then set the base address/length of the descriptor (dpmi_set_segment_base_address, dpmi_set_segment_limit)
The other mail already mentioned the names of the corresponding GO32 functions.
As usual there should be an example program around (both for the GO32 unit and the DPMI units)
Under real DOS with BP7 it is O.K.
As another reader already pointed out, FPC programs always runs in protected mode, so it's quite common that such programs won't work (actually it'd be quite surprising if they worked right away).
Sorry, i know this is not really question to FPC, but maybe somebody
could help me. The same problem i got with calling ASPI entry point.
I believe that the reasons/solutions are the same for both problems.
Note that as you may notice these units are older (never thought they'd be of much use again), e.g. ~3 years, so there might be small problems when compiling.
Hope this helps.
Regards,
Thomas
