Hi all,

I was hoping someone could help me with a question.  I want to place data at a specific location in memory.  I am writing this program with no run-time support, so dynamic memory allocation is out of the question.  The location I want to place data in is in a seperate segment, so I believe I will need to use a far pointer.  I searched this site and found the __far pointer keyword.  I figure I need to create a pointer using the __far keyword and place the address in it following the instructions I found on this site.  I am going to need to do this in both real mode and protected mode.  For example, say I am executing code in real mode located in segment 0900h and I want to place data in segment 1200h at offset 0000h.  How would I do this?  I know protected mode is different with its global descriptor table but is this also possible in protected mode.  I don't know if I explained this carefully enough, so tell me if I need to clarify.

Thanks!

"IR" <IR_member@pathlink.com> wrote in message news:cmj6r3$2fld$1@digitaldaemon.com...
> Hi all,
>
> I was hoping someone could help me with a question.  I want to place data
at a
> specific location in memory.  I am writing this program with no run-time support, so dynamic memory allocation is out of the question.  The
location I
> want to place data in is in a seperate segment, so I believe I will need
to use
> a far pointer.  I searched this site and found the __far pointer keyword.
I
> figure I need to create a pointer using the __far keyword and place the
address
> in it following the instructions I found on this site.  I am going to need
to do
> this in both real mode and protected mode.  For example, say I am
executing code
> in real mode located in segment 0900h and I want to place data in segment
1200h
> at offset 0000h.  How would I do this?  I know protected mode is different
with
> its global descriptor table but is this also possible in protected mode.
I
> don't know if I explained this carefully enough, so tell me if I need to clarify.

You'll need to use a locator to map the relocatable executable to a specific address. Also, use the 'L' memory model so each source file's code and data are placed in separate segments.

Is there any way just to write data to a far segment using a far pointer?


In article <cmj7qc$2h2n$1@digitaldaemon.com>, Walter says...
>
>
>"IR" <IR_member@pathlink.com> wrote in message news:cmj6r3$2fld$1@digitaldaemon.com...
>> Hi all,
>>
>> I was hoping someone could help me with a question.  I want to place data
>at a
>> specific location in memory.  I am writing this program with no run-time support, so dynamic memory allocation is out of the question.  The
>location I
>> want to place data in is in a seperate segment, so I believe I will need
>to use
>> a far pointer.  I searched this site and found the __far pointer keyword.
>I
>> figure I need to create a pointer using the __far keyword and place the
>address
>> in it following the instructions I found on this site.  I am going to need
>to do
>> this in both real mode and protected mode.  For example, say I am
>executing code
>> in real mode located in segment 0900h and I want to place data in segment
>1200h
>> at offset 0000h.  How would I do this?  I know protected mode is different
>with
>> its global descriptor table but is this also possible in protected mode.
>I
>> don't know if I explained this carefully enough, so tell me if I need to clarify.
>
>You'll need to use a locator to map the relocatable executable to a specific address. Also, use the 'L' memory model so each source file's code and data are placed in separate segments.
>
>

Using MK_FP(), you can create a far pointer to any memory location, then read and write that location.

"IR" <IR_member@pathlink.com> wrote in message news:cmjcjc$2nnu$1@digitaldaemon.com...
> Is there any way just to write data to a far segment using a far pointer?

Im sorry to keep bothering you but I am still new to this and am trying to learn.

I know how I would read data from that location but how would you write.  Thanks again.




In article <cmjt3m$au8$1@digitaldaemon.com>, Walter says...
>
>Using MK_FP(), you can create a far pointer to any memory location, then read and write that location.
>
>"IR" <IR_member@pathlink.com> wrote in message news:cmjcjc$2nnu$1@digitaldaemon.com...
>> Is there any way just to write data to a far segment using a far pointer?
>
>

char __far *p = MK_FP(0x1200, 0x40);
*p = 6;    // writes 6 to 1200:0040


"IR" <IR_member@pathlink.com> wrote in message news:cmk0u6$fl9$1@digitaldaemon.com...
> Im sorry to keep bothering you but I am still new to this and am trying to learn.
>
> I know how I would read data from that location but how would you write.
Thanks
> again.
>
>
>
>
> In article <cmjt3m$au8$1@digitaldaemon.com>, Walter says...
> >
> >Using MK_FP(), you can create a far pointer to any memory location, then read and write that location.
> >
> >"IR" <IR_member@pathlink.com> wrote in message news:cmjcjc$2nnu$1@digitaldaemon.com...
> >> Is there any way just to write data to a far segment using a far
pointer?
> >
> >
>
>

The program has to include dos.h in order to use MK_FP().

Do you know if MK_FP() uses any DOS interrupts or any other DOS functions?

The reason I ask is because I'm writing a program with no underlying OS support.

If it does use some type of DOS support, can you tell me how to set the far pointer without using MK_FP().

Thanks





In article <cmlsjq$56a$1@digitaldaemon.com>, Walter says...
>
>char __far *p = MK_FP(0x1200, 0x40);
>*p = 6;    // writes 6 to 1200:0040
>
>
>"IR" <IR_member@pathlink.com> wrote in message news:cmk0u6$fl9$1@digitaldaemon.com...
>> Im sorry to keep bothering you but I am still new to this and am trying to learn.
>>
>> I know how I would read data from that location but how would you write.
>Thanks
>> again.
>>
>>
>>
>>
>> In article <cmjt3m$au8$1@digitaldaemon.com>, Walter says...
>> >
>> >Using MK_FP(), you can create a far pointer to any memory location, then read and write that location.
>> >
>> >"IR" <IR_member@pathlink.com> wrote in message news:cmjcjc$2nnu$1@digitaldaemon.com...
>> >> Is there any way just to write data to a far segment using a far
>pointer?
>> >
>> >
>>
>>
>
>

From dos.h:

#define MK_FP(seg,offset) \
        ((void __far *)(((unsigned long)(seg)<<16) | (unsigned)(offset)))

So, no, it does not use DOS functions.


"IR" <IR_member@pathlink.com> wrote in message news:cmo00b$kjq$1@digitaldaemon.com...
> The program has to include dos.h in order to use MK_FP().
>
> Do you know if MK_FP() uses any DOS interrupts or any other DOS functions?
>
> The reason I ask is because I'm writing a program with no underlying OS
support.
>
> If it does use some type of DOS support, can you tell me how to set the
far
> pointer without using MK_FP().
>
> Thanks
>
>
>
>
>
> In article <cmlsjq$56a$1@digitaldaemon.com>, Walter says...
> >
> >char __far *p = MK_FP(0x1200, 0x40);
> >*p = 6;    // writes 6 to 1200:0040
> >
> >
> >"IR" <IR_member@pathlink.com> wrote in message news:cmk0u6$fl9$1@digitaldaemon.com...
> >> Im sorry to keep bothering you but I am still new to this and am trying
to
> >> learn.
> >>
> >> I know how I would read data from that location but how would you
write.
> >Thanks
> >> again.
> >>
> >>
> >>
> >>
> >> In article <cmjt3m$au8$1@digitaldaemon.com>, Walter says...
> >> >
> >> >Using MK_FP(), you can create a far pointer to any memory location,
then
> >> >read and write that location.
> >> >
> >> >"IR" <IR_member@pathlink.com> wrote in message news:cmjcjc$2nnu$1@digitaldaemon.com...
> >> >> Is there any way just to write data to a far segment using a far
> >pointer?
> >> >
> >> >
> >>
> >>
> >
> >
>
>