Date:	Thu, 10 Apr 1997 17:11:19 -0300
Message-Id:	<199704102011.RAA14915@ada.info.unlp.edu.ar>
Mime-Version:	1.0
To:	djgpp AT delorie DOT com
From:	Raul Champredonde <rchampre AT ada DOT info DOT unlp DOT edu DOT ar>
Subject:	Ada, C and interrupts
Cc:	rchampre AT ada DOT info DOT unlp DOT edu DOT ar

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                                                        10th. April, 1997
   
   
   I mail to you because I need some help. I have some trouble when I intended
to run my program developed in ADA and C.
   
   I programed some functions in `C' to do interrupts and use NETBIOS service routines.
   My `C' program run well.
   Later I imported from `C' to ADA95 the functions using pragma 'Import'. Because ADA95
   run in protected mode I had problems with ADA program.
   
   I want to call a NETBIOS functions, previously loaded in the interrupts vector, 
which requires a pointer to a buffer `ES:BX' register pair. Interrupt number is 5CH.
   Questions are: 
 
 *Q1* How do I get the segment to put into the `ES' register? 
 
 *Q2* How can I obtein the buffer's address when I alloc memory using `malloc' function 
since it returned me an address formated in 20 bits (lineal address) and I need 
an adress formated like this: segment:offset (32 bits). NETBIOS functions 
requests ES and BX to be setted.

 *Q3* How can I run ada95 in real mode?. Exist any way to run ada95 in non protected mode?
 
 I found some answers in a file called `DJGPPFAQ.TXT' :

 **1st. A** :  Use `int86x', then just put the address of your buffer into the register 
which expects the offset (`regs.x.bx') and forget about the segment.These functions 
are processed specially by the library, which will take care of the rest.
 
 * I did it and the program crashed showing an ERROR: `General Protection Fault'.

 **2nd. A** :  Call `__dpmi_int,' and then put into that register pair an address 
 of some buffer in *conventional* memory (in the first 1 MByte).The buffer's size 
 that I need is 64 bytes only.

 * My program doesn't crash but I can't obtein the segment and the offset to send as 
 parameter to the function `__dmpi_int'.

 **3rd. A** :  I found a method for transform lineal address to segment-offset address:
   
   OFFSET  = (LINEAL_ADDRESS)&000Fh
   SEGMENT = (shift_right(LINEAL_ADDRSS,4))&FFFFh

   in C:

   offset  = lineal_address&0x000F;
   segment = (lineal_address>>4)&0xFFFF;
                                                        
 * I did it and then I used `__dpmi_int'. The program didn't show any error 
 but  it didn't call NETBIOS functions.
 
 **4th. A** :  Use the transfer buffer. That buffer is used for all DOS/BIOS 
services supported by DJGPP, and it resides in conventional memory.  

 * How can I write into this buffer?

 * Should I pass as parameters to the interrupt these addresses :

     dpmi_regs.x.bx =
      _go32_info_block.linear_address_of_transfer_buffer & 0x0f;
     dpmi_regs.x.es =
      (_go32_info_block.linear_address_of_transfer_buffer >> 4) & 0xffff;

 **5th. A** :  Allocate my own buffer in conventional memory with a call to the
`__dpmi_allocate_dos_memory' library function. It returns me the segment of
the allocated block (the offset is zero).  

  * OK, I've the offset and the segment but when I intended write into the buffer 
I get "Segmentation Violation and "General Protection Fault".  


   I look forward to hearing from you and thank you in advance.





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