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Text File | 1988-08-11 | 27.1 KB | 819 lines

Microsoft Systems Journal Volume 2; Issue 1; March, 1987 Code Listings For: Expanded Memory pp. 21-32 Author(s): Marion Hansen, Bill Krueger, Nick Stuecklen Title: Expanded Memeory: Writing Programs That Break the 640K Barrier ============================================================================== ============================================================================== Figure 3: Main Program ============================================================================== #include <dos.h> #include <stdio.h> #define EMM_INT 0x67 /* EMM interrupt number */ #define GET_PAGE_FRAME_BASE 0x41 /* EMM func = get page frame base address */ #define GET_FREE_COUNT 0x42 /* EMM Func = get unallocated pages count */ #define ALLOCATE_PAGES 0x43 /* EMM Func = allocates pages */ #define MAP_PAGES 0x44 /* EMM Func = map pages */ #define DEALLOCATE_PAGES 0x45 /* EMM Func = deallocate pages */ #define GET_INT_VECTOR 0x35 /* DOS func = get interrupt vector */ #define DEVICE_NAME_LEN 8 /* Number of chars in device driver name field */ #define VIDEO_RAM_SIZE 4000 /* Total bytes in video RAM (char/attr) */ #define VIDEO_RAM_BASE 0xB0000000 /* Video RAM start address (MDA) */ union REGS input_regs, output_regs; /* Regs used for calls to EMM and DOS */ struct SREGS segment_regs; unsigned int emm_status; /* Status returned by EMM */ main () { unsigned int i; long target_time, current_time; char *video_ram_ptr = {VIDEO_RAM_BASE}; /* Pointer to video RAM */ unsigned int emm_handle; /* EMM handle */ char *expanded_memory_ptr; /* Pointer to expanded memory */ /* Ensure that the Expanded Memory Manager software is installed on the user's system. */ detect_emm(); /* Get a page of expanded memory. */ get_expanded_memory_page (&expanded_memory_ptr, &emm_handle); /* Copy the current video RAM contents to expanded memory. */ memcpy (expanded_memory_ptr, video_ram_ptr, VIDEO_RAM_SIZE); /* Clear the screen to nulls. */ memset (video_ram_ptr, '\0', VIDEO_RAM_SIZE); /* Delay for 1 second so the user can see the blanked screen. */ time (¤t_time); target_time = current_time + 1; while (current_time < target_time) { time (¤t_time); } /* Restore the video RAM contents from expanded memory. */ memcpy (video_ram_ptr, expanded_memory_ptr, VIDEO_RAM_SIZE); /* Deallocate the expanded memory page */ release_expanded_memory_page (emm_handle); exit(0); } ============================================================================== ============================================================================== ============================================================================== Figure 4: Detect_EMM Subroutine ============================================================================== detect_emm () { static char EMM_device_name [DEVICE_NAME_LEN] = {"EMMXXXX0"}; char *int_67_device_name_ptr; /* Determine the address of the routine associated with INT 67 hex. */ input_regs.h.ah = GET_INT_VECTOR; /* DOS function */ input_regs.h.al = EMM_INT; /* EMM interrupt number */ intdosx (&input_regs, &output_regs, &segment_regs); int_67_device_name_ptr = (segment_regs.es * 65536) + 10; /* Create ptr to device name field */ /* Compare the device name with the known EMM device name. */ if(memcmp(EMM_device_name,int_67_device_name_ptr,DEVICE_NAME_LEN) !=0) { printf ("\x07Abort: EMM device driver not installed\n"); exit(0); } } ============================================================================== ============================================================================== ============================================================================== Figure 5: Check_Status Subprocedure ============================================================================== check_status (emm_status) unsigned int emm_status; { static char *emm_error_strings[] = { "no error", "EMM software malfunction", "EMM hardware malfunction", "RESERVED", "Invalid EMM handle", "Invalid EMM function code", "All EMM handles being used", "Save/restore page mapping context error", "Not enough expanded memory pages", "Not enough unallocated pages", "Can not allocate zero pages", "Logical page out of range", "Physical page out of range", "Page mapping hardware state save area full", "Page mapping hardware state save area already has handle", "No handle associated with the page mapping hardware state save area", "Invalid subfunction" }; /* IF EMM error, THEN print error message and EXIT */ if (emm_status != 0) /* IF EMM error... */ { emm_status -= 0x7F; /* Make error code zero-based */ printf ("\x07Abort: EMM error = "); /* Issue error prefix */ printf ("%s\n", emm_error_strings[emm_status]); /* Issue actual error message */ exit(0); /* And then exit to DOS */ } } ============================================================================== ============================================================================== ============================================================================== Figure 6: Get_Expanded_Memory_Page Subprocedure ============================================================================== get_expanded_memory_page (expanded_memory_ptr_ptr, emm_handle_ptr) unsigned int *emm_handle_ptr; /* 16 bit handle returned by EMM */ char *(*expanded_memory_ptr_ptr); /* Pointer to expanded memory page */ { unsigned int page_frame_base; /* Expanded memory page frame base */ unsigned int physical_page = {0}; /* Physical page number */ /* Get unallocated pages count. */ input_regs.h.ah = GET_FREE_COUNT; /* EMM function */ int86x (EMM_INT, &input_regs, &output_regs, &segment_regs); emm_status = output_regs.h.ah; check_status(emm_status); /* Check for errors */ if (output_regs.x.bx < 1) /* Check unallocated page count */ { printf ("\x07Abort: insufficient unallocated expanded memory pages\n"); exit(0); } /* Allocate the specified number of pages. */ input_regs.h.ah = ALLOCATE_PAGES; /* EMM function */ input_regs.x.bx = 1; /* Number of pages to allocate */ int86x (EMM_INT, &input_regs, &output_regs, &segment_regs); emm_status = output_regs.h.ah; check_status(emm_status); /* Check for errors */ *emm_handle_ptr = output_regs.x.dx; /* Get EMM handle */ /* Map the logical page into physical page 0. */ input_regs.h.ah = MAP_PAGES; /* EMM function */ input_regs.h.al = 0; /* Logical page number */ input_regs.x.bx = physical_page; /* Physical page number */ input_regs.x.dx = *emm_handle_ptr; /* EMM handle */ int86x (EMM_INT, &input_regs, &output_regs, &segment_regs); emm_status = output_regs.h.ah; check_status(emm_status); /* Check for errors */ /* Determine the page frame address. */ input_regs.h.ah = GET_PAGE_FRAME_BASE; /* EMM function */ int86x (EMM_INT, &input_regs, &output_regs, &segment_regs); emm_status = output_regs.h.ah; check_status(emm_status); /* Check for errors */ *expanded_memory_ptr_ptr = (output_regs.x.bx * 65536) + (physical_page * 16 * 1024); /* Set the expanded memory ptr */ } ============================================================================== ============================================================================== ============================================================================== Figure 7: Release_Expanded_Memory_Page Subroutine ============================================================================== release_expanded_memory_page (emm_handle) unsigned int emm_handle; /* Handle identifying which page set to deallocate */ { /* Release the expanded memory pages by deallocating the handle associated with those pages. */ input_regs.h.ah = DEALLOCATE_PAGES; /* EMM function */ input_regs.x.dx = emm_handle; /* EMM handle passed in DX */ int86x (EMM_INT, &input_regs, &output_regs, &segment_regs); emm_status = output_regs.h.ah; check_status(emm_status); /* Check for errors */ } ============================================================================== ============================================================================== ============================================================================== Figure 8: Kernel Module ============================================================================== CODE SEGMENT PARA PUBLIC 'CODE' ORG 100h ASSUME CS:CODE, DS:DATA, ES:NOTHING, SS:STACK max_proc_entries EQU 64 pseudo_over_struct STRUC proc_data_segment DW ? proc_extra_segment DW ? proc_entry_count DW ? proc_entry_ptr DD max_proc_entries DUP (?) pseudo_over_struct ENDS main PROC NEAR MOV AX, DATA ; Segment initialization MOV DS, AX check_for_emm_loaded: CALL test_for_EMM ; Use the "interrupt vector" JE get_emm_page_frame ; technique to determine JMP emm_err_exit ; whether EMM is loaded get_emm_page_frame: MOV AH, 41h ; Get the page frame base INT 67h ; address from EMM OR AH, AH JZ allocate_64K JMP emm_err_exit allocate_64K: MOV exp_mem_segment, BX ; Allocate 4 pages of expand- MOV AH, 43h ; ed memory for this example. MOV BX, 4 ; More can be allocated de- INT 67h ; pending on the number of OR AH, AH ; overlays to be loaded. JZ map_64K ; Actually, in this case, JMP emm_err_exit ; only a single page is re- ; quired because the example ; pseudo-overlay is extreme- ; ly small. map_64K: MOV handle, DX ; Map in the first 4 logical MOV CX, 4 ; pages at physical pages 0 map_pages_loop: ; through 3 MOV AH, 44h ; logical page 0 at MOV BX, CX ; physical page 0 DEC BX ; logical page 1 at MOV AL, BL ; physical page 1 MOV DX, handle ; logical page 2 at INT 67h ; physical page 2 OR AH, AH ; logical page 3 at LOOPE map_pages_loop ; physical page 3 JE init_load_struct ; If additional overlays were JMP emm_err_exit ; required, each overlay ; would be loaded after map- ; ping and a new set of ; logical pages would be ; mapped at the same ; physical pages. init_load_struct: MOV ES, exp_mem_segment ; Initialize pseudo-overlay MOV DI, 0 ; environment and procedure MOV CX, (SIZE pseudo_over_struct) ; pointer area. This struc- MOV AL, 0 ; ture begins at the page REP STOSB ; frame segment address. MOV AX, (SIZE pseudo_over_struct) ; Compute the load address ADD AX, 000Fh ; within expanded memory for AND AX, 0FFF0h ; the overlay. The address is MOV CX, 4 ; rounded up to the next SHR AX, CL ; higher paragraph boundary ADD AX, exp_mem_segment ; immediately following the MOV parm_block.load_segment, AX ; pseudo-overlay environment MOV parm_block.reloc_factor, AX ; & procedure pointer ; structure. This computa- ; tion takes into account ; the maximum number of ; procedure entry points ; which the pseudo-overlay ; is going to return to ; this program. MOV WORD PTR entry_point[0], 100h ; Build .COM file entry MOV WORD PTR entry_point[2], AX ; point MOV AH, 4Bh ; Load the pseudo-overlay MOV AL, 03h ; using the DOS "load LEA DX, pseudo_over_name ; overlay" function PUSH DS POP ES LEA BX, parm_block INT 21h JC emm_err_exit PUSH DS ; Transfer control to the PUSH ES ; loaded pseudo-overlays CALL DWORD PTR entry_point ; initialization code POP ES POP DS OR AH, AH JZ call_over_procedures JMP emm_err_exit call_over_procedures: MOV ES, exp_mem_segment ; As an example of passing MOV BX, 0 ; control to a procedure MOV DI, 0 ; existing in expanded MOV CX, ES:[BX].proc_entry_count ; memory, each procedure con- JCXZ deallocate_exp_memory ; tained in the overlay will ; be called in sequence. ; Obviously, a single pro- ; cedure could be called ; just as easily. pseudo_over_call_loop: PUSH BX PUSH CX PUSH DI PUSH ES PUSH DS LDS AX, ES:[BX+DI].proc_entry_ptr MOV WORD PTR CS:tp_ent_ptr[0], AX MOV WORD PTR CS:tp_ent_ptr[2], DS MOV AX, 123 ; Pass 2 numbers to MOV DX, 23 ; the procedures MOV DS, ES:[BX].proc_data_segment ; Set up pseudo-overlays MOV ES, ES:[BX].proc_extra_segment ; segment environment CALL DWORD PTR CS:tp_ent_ptr ; Call each procedure POP DS POP ES POP DI POP CX POP BX ADD DI, 4 ; Adjust index to the next LOOP pseudo_over_call_loop ; procedure (4 bytes long) ; pointer & loop till all ; have been called deallocate_exp_memory: MOV AH, 45h ; Return the allocated MOV DX, handle ; pages to the expanded INT 67h ; memory manager OR AH, AH JNZ emm_err_exit exit: MOV AH, 4Ch ; Return a normal exit code MOV AL, 0 INT 21h emm_err_exit: MOV AL, AH ; Display the fact that MOV AH, 09h ; an EMM error occurred LEA DX, emm_err_msg ; Go to the normal exit INT 21h JMP exit tp_ent_ptr DD ? ; CS relative far pointer ; used for transfer to the main ENDP ; procedures in the ; pseudo_overlay ============================================================================== ============================================================================== ============================================================================== Figure 9: Procedure to Test for the Presence of EMM ============================================================================== test_for_EMM PROC NEAR MOV AX, 3567h ; Issue "get interrupt vector" INT 21h MOV DI, 000Ah ; Use the SEGMENT in ES ; returned by DOS, place ; the "device name field" ; OFFSET in DI. LEA SI, EMM_device_name ; Place the OFFSET of the EMM ; device name string in SI, ; the SEGMENT is already in DS. MOV CX, 8 ; Compare the name strings CLD ; Return the status of the REPE CMPSB ; compare in the ZERO flag RET test_for_EMM ENDP CODE ENDS ============================================================================== ============================================================================== ============================================================================== Figure 10: Pseudo-overlay Module ============================================================================== CODE SEGMENT PARA PUBLIC 'CODE' ASSUME CS:CODE, DS:DATA ORG 100h actual_proc_entries EQU 2 overlay_entry_struct STRUC proc_data_segment DW ? proc_extra_segment DW ? proc_entry_count DW ? proc_entry_ptr DD actual_proc_entries DUP (?) overlay_entry_struct ENDS ============================================================================== ============================================================================== ============================================================================== Figure 11: Procedure to Identify Overlay ============================================================================== command_line_entry_point PROC NEAR MOV AX, DATA ; Set up local data MOV DS, AX ; segment LEA DX, overlay_err_msg ; Display overlay error MOV AH, 09h ; message INT 21h MOV AX, 4C00h ; Exit back to DOS INT 21h command_line_entry_point ENDP ============================================================================== ============================================================================== ============================================================================== Figure 12: Data Segment for the Pseudo-overlay Module ============================================================================== DATA SEGMENT PARA PUBLIC 'DATA' sum_msg DB 0Dh, 0Ah, 'Sum of numbers = ', '$' diff_msg DB 0Dh, 0Ah, 'Difference of numbers = ', '$' overlay_err_msg DB 'Overlay cannot be executed via the command line$' powers_of_ten DW 10000, 1000, 100, 10, 1 DATA ENDS END command_line_entry_point ============================================================================== ============================================================================== ============================================================================== Figure 13: Pseudo-overlay Data Structure Initialization Procedure ============================================================================== initialization PROC FAR MOV AX, DATA ; Set up a local MOV DS, AX ; data segment MOV AH, 41h ; Get the page INT 67h ; frame segment OR AH, AH ; address from EMM JNZ error MOV ES, BX ; Create a pointer MOV DI, 0 ; to the expanded ; memory page frame ; segment address MOV ES:[DI].proc_data_segment, DS ; Return local data MOV ES:[DI].proc_extra_segment, DS ; & extra segment ; back to the kernel MOV WORD PTR ES:[DI].proc_entry_count, 2 ; Return the number ; of local call- ; able procedures ; back to kernel MOV WORD PTR ES:[DI].proc_entry_ptr[0], OFFSET sum ; Return a far MOV WORD PTR ES:[DI].proc_entry_ptr[2], SEG sum ; pointer to each MOV WORD PTR ES:[DI].proc_entry_ptr[4], OFFSET diff ; local callable MOV WORD PTR ES:[DI].proc_entry_ptr[6], SEG diff ; procedure in the ; pseudo-overlay ; back to kernel exit: MOV AH, 0 ; Set status in AH ; = passed error: RET ; Return status ; in AH initialization ENDP ============================================================================== ============================================================================== ============================================================================== Figure 14: Procedure to Add AX and DX ============================================================================== sum PROC FAR ADD AX, DX ; Add numbers PUSH AX ; Display sum message LEA DX, sum_msg MOV AH, 09h INT 21h POP AX CALL display_result ; Display sum RET sum ENDP ============================================================================== ============================================================================== ============================================================================== Figure 15: Procedure to Subtract AX and DX ============================================================================== diff PROC FAR SUB AX, DX ; Subtract numbers PUSH AX ; Display difference message LEA DX, diff_msg MOV AH, 09h INT 21h POP AX CALL display_result ; Display difference RET diff ENDP ============================================================================== ============================================================================== ============================================================================== Figure 16: Procedure to Display Number in AX in Decimal ============================================================================== display_result PROC NEAR LEA DI, powers_of_ten MOV CX, 5 display_loop: XOR DX, DX ; Divide the number passed DIV WORD PTR [DI] ; in AX by descending powers of ten ADD AL, '0' ; Convert digit to ASCII PUSH DX ; Output the digit MOV DL, AL MOV AH, 02h INT 21h POP AX ADD DI, 2 LOOP display_loop RET display_result ENDP ============================================================================== ============================================================================== ============================================================================== Figure 17: Data and Stack Segment for the Kernel and the Pseudo-overlay ============================================================================== DATA SEGMENT PARA PUBLIC 'DATA' emm_err_msg DB 'EMM error occurred$' ; EMM diagnostic message pseudo_over_name DB 'OVERLAY.EXE', 0 ; Name of pseudo-overlay EMM_device_name DB 'EMMXXXX0' ; Standard EMM device name exp_mem_segment DW ? ; Temp for expanded ; memory page frame ; segment address handle DW ? ; Temp for handle allo- ; cated to the kernel entry_point DD ? ; Far pointer to the ; entry point for a .COM ; file parm_block_struct STRUC ; Structure definition load_segment DW ? ; for a "load overlay" reloc_factor DW ? ; parameter block parm_block_struct ENDS parm_block parm_block_struct <> ; The actual parameter ; block DATA ENDS STACK SEGMENT PARA STACK 'STACK' local_stack DW 256 DUP ('^^') STACK ENDS END main ==============================================================================