INT 21h - Exec function: Out Of Memory

[Peter Swinkels]

EDIT:
I solved the problem with INT 21h, 48h (Allocate Memory Blocks)
I should write MOV ah, 48h, not MOV ax, 48h
That only leaves the problem with Exec function to be solved...

I am trying to write a routine that can run other programs but whenever I run this program INT 21h, 4Bh (Exec Load and Execute Program) reports that the program is out of memory. (error code 8) As far as I understand it I need to allocate memory for another program before running it. I can't find any useful information in Helppc or on the internet though. I tried allocating memory with INT 21h, 48h but the program exits instead of allocating memory whenever it attempts to execute that function.

The program: (All numbers are in DECIMAL notation! Which means that INT 21h, 4Bh is referred to as INT 33, 75 in the code.)

ORG 256
Main:
	; Executes the program.
	MOV ah, 75		; Load and Execute Program
	MOV al, 0		; Load and execute.
	MOV dx, .Program	; The path and file name of the program to execute.
	MOV bx, ds		; Parameter block.
	MOV es, bx		;
	MOV bx, .Parameters	;
	INT 33			; DOS functions interrupt.
	JMP ErrorTrap
RET

.Parameters RESB 22
.Program db "command.com", 0



;+---------------------------------------------------+
;| Error Trap - Displays the error code. 	     |
;| [Parameters in:]			 	     |
;| Name:	Description:		Type:	     |
;| ax		The error code.		CPU register |
;+---------------------------------------------------+

ErrorTrap:
	; Converts the error code to a user readable format.
	PUSH ax			; The error code.
	CALL cv256to16		; Converts value to user readable format.
	POP DWORD [.ErrorCode]	;

	; Displays the error code.
	MOV ah, 9		; Print String.
	MOV dx, .ErrorCode	;
	INT 33			; DOS functions interrupt.
RET

.ErrorCode db "0000", 13, 10, "$"



;+-------------------------------------------------------------------------------+
;| Convert Byte to Hexadecimal - Converts byte values to hexadecimal number.     |
;| [Parameters in:]                                                 		 |
;| Name:	Description:				Type:    		 |
;| Number	Byte values to be converted.            2 Byte number (by value) |
;| Parameters out:]                                                     	 |
;| Name:	Description:				Type:    		 |
;| Hexadecimal	Converted hexadecimal number.		4 Byte string (by value) |
;+-------------------------------------------------------------------------------+

cv256to16:
	POP WORD [.ReturnAddress]
	POP WORD [.ByteVal]

	MOV bx, 0					; Digit = 0
	MOV cl, 12					; BitShift = 12
	MOV dx, 64410					; BitMask = 64410
		.GetHexDigits:
			MOV ax, [.ByteVal]		;
			AND ax, dx			; Extract a 4 bit value from the byte values.
			SHR ax, cl			;
			MOV si, ax			;
			MOV al, [.HexDigits + si]	; Get the hexadecimal digit for the 4 bit value.
			MOV [.HexNumber + bx], al	;
			SHR dx, 4			; Adjust BitMask
			SUB cl, 4			; and BitShift.
			INC bx				; Next digit.
			CMP bx, 4			; Check for last digit.
		JNE .GetHexDigits

	PUSH DWORD [.HexNumber]
	PUSH WORD [.ReturnAddress]
RET

.ByteVal dw 0
.HexNumber db "0000"
.HexDigits db "0123456789ABCDEF"
.ReturnAddress dw 0

[Maven]

EDIT:
I solved the problem with INT 21h, 48h (Allocate Memory Blocks)
I should write MOV ah, 48h, not MOV ax, 48h
That only leaves the problem with Exec function to be solved...

I am trying to write a routine that can run other programs but whenever I run this program INT 21h, 4Bh (Exec Load and Execute Program) reports that the program is out of memory. (error code 8) As far as I understand it I need to allocate memory for another program before running it. I can't find any useful information in Helppc or on the internet though. I tried allocating memory with INT 21h, 48h but the program exits instead of allocating memory whenever it attempts to execute that function.

The program: (All numbers are in DECIMAL notation! Which means that INT 21h, 4Bh is referred to as INT 33, 75 in the code.)

ORG 256
Main:
	; Executes the program.
	MOV ah, 75		; Load and Execute Program
	MOV al, 0		; Load and execute.
	MOV dx, .Program	; The path and file name of the program to execute.
	MOV bx, ds		; Parameter block.
	MOV es, bx		;
	MOV bx, .Parameters	;
	INT 33			; DOS functions interrupt.
	JMP ErrorTrap
RET

.Parameters RESB 22
.Program db "command.com", 0



;+---------------------------------------------------+
;| Error Trap - Displays the error code. 	     |
;| [Parameters in:]			 	     |
;| Name:	Description:		Type:	     |
;| ax		The error code.		CPU register |
;+---------------------------------------------------+

ErrorTrap:
	; Converts the error code to a user readable format.
	PUSH ax			; The error code.
	CALL cv256to16		; Converts value to user readable format.
	POP DWORD [.ErrorCode]	;

	; Displays the error code.
	MOV ah, 9		; Print String.
	MOV dx, .ErrorCode	;
	INT 33			; DOS functions interrupt.
RET

.ErrorCode db "0000", 13, 10, "$"



;+-------------------------------------------------------------------------------+
;| Convert Byte to Hexadecimal - Converts byte values to hexadecimal number.     |
;| [Parameters in:]                                                 		 |
;| Name:	Description:				Type:    		 |
;| Number	Byte values to be converted.            2 Byte number (by value) |
;| Parameters out:]                                                     	 |
;| Name:	Description:				Type:    		 |
;| Hexadecimal	Converted hexadecimal number.		4 Byte string (by value) |
;+-------------------------------------------------------------------------------+

cv256to16:
	POP WORD [.ReturnAddress]
	POP WORD [.ByteVal]

	MOV bx, 0					; Digit = 0
	MOV cl, 12					; BitShift = 12
	MOV dx, 64410					; BitMask = 64410
		.GetHexDigits:
			MOV ax, [.ByteVal]		;
			AND ax, dx			; Extract a 4 bit value from the byte values.
			SHR ax, cl			;
			MOV si, ax			;
			MOV al, [.HexDigits + si]	; Get the hexadecimal digit for the 4 bit value.
			MOV [.HexNumber + bx], al	;
			SHR dx, 4			; Adjust BitMask
			SUB cl, 4			; and BitShift.
			INC bx				; Next digit.
			CMP bx, 4			; Check for last digit.
		JNE .GetHexDigits

	PUSH DWORD [.HexNumber]
	PUSH WORD [.ReturnAddress]
RET

.ByteVal dw 0
.HexNumber db "0000"
.HexDigits db "0123456789ABCDEF"
.ReturnAddress dw 0

Try including the full path to the file you want to execute. DirveName:\Path\filename

[Peter Swinkels]

Well, the problem isn't that the program I want to execute can't be found by DOS, the problem is that DOS claims there isn't enough memory to load and the execute program. I find that highly unlikely. It's more likely I did something wrong in the code. I did some fiddeling with the Allocate Memory function, it won't allocate even one paragraph (16 bytes.) Just like the EXEC function it claims there isn't enough memory.

Just to be on the safe side, I tried using the full path as you suggested. I got the same error again.

BTW:
Perhaps I should have mentioned that the code I posted in my previous message in this thread returns an error code if an error occurs.
The error codes are DOS error codes. According to HelpPC these are important when using int 21h:

01 Invalid function number
02 File not found
03 Path not found
04 Too many open files (no handles left)
05 Access denied
06 Invalid handle
07 Memory control blocks destroyed
08 Insufficient memory
09 Invalid memory block address
0A Invalid environment
0B Invalid format
0C Invalid access mode (open mode is invalid)
0D Invalid data
0E Reserved
0F Invalid drive specified
10 Attempt to remove current directory
11 Not same device
12 No more files

[Maven]

Well, the problem isn't that the program I want to execute can't be found by DOS, the problem is that DOS claims there isn't enough memory to load and the execute program. I find that highly unlikely. It's more likely I did something wrong in the code. I did some fiddeling with the Allocate Memory function, it won't allocate even one paragraph (16 bytes.) Just like the EXEC function it claims there isn't enough memory.

Just to be on the safe side, I tried using the full path as you suggested. I got the same error again.

BTW:
Perhaps I should have mentioned that the code I posted in my previous message in this thread returns an error code if an error occurs.
The error codes are DOS error codes. According to HelpPC these are important when using int 21h:

01 Invalid function number
02 File not found
03 Path not found
04 Too many open files (no handles left)
05 Access denied
06 Invalid handle
07 Memory control blocks destroyed
08 Insufficient memory
09 Invalid memory block address
0A Invalid environment
0B Invalid format
0C Invalid access mode (open mode is invalid)
0D Invalid data
0E Reserved
0F Invalid drive specified
10 Attempt to remove current directory
11 Not same device
12 No more files

You may want to try posting at hutchs board, under the 16bit forum.
http://www.masmforum.com/