Sunday, October 25, 2009 10:37 AM,

on

Ooops!  In the example I sent late last night, I made a change to the machine 
code and forgot to fix one line of assembly language code.  In the example, 

A	.FILL x400B  should be
A	.FILL x4007

The machine code is correct.

Yale Patt
======================
On Sun, Oct 25, 2009 at 05:18:50AM -0500, Yale N. Patt wrote:
> 
> There still seems to be confusion among many students about the 
> pseudo-op .BLKW.  If you feel you understand it, please feel free to 
> simply delete this message and move on.
> 
> Now then:
> 
> We showed in class last week when we assembled a program that when the 
> assembler sees .BLKW k, for example, the assembler simply reserves the 
> next k locations of memory before proceeding to the next assembly 
> language instruction.
> 
> Example:
> 
> 	.ORIG x4000
> 	AND   R0,R0,#0
> 	ADD   R1,R0,#1
> 	LD    R7,A
> 	STR   R0,R7,#0
> 	ADD   R7,R7,#1
> 	STR   R1,R7,#0
> 	TRAP  x25
> 	.BLKW 3
> A	.FILL x400B
> 	.END
> 
> The assembler would go through this assembly language program, line by 
> line, and generate an object file as follows:
> 
> x4000: 0101 000 000 1 00000
> x4001: 0001 001 000 1 00001
> x4002: 0010 111 000000111
> x4003: **** 000 111 000000 ; My book is not with me, so I can not look STR !
> x4004: 0001 111 111 1 00001
> x4005: **** 001 111 1 00000
> x4006: 1111 0000 0010 0101
> x4007: reserved space, nothing of consequence stored here
> x4008: reserved space, nothing of consequence stored here
> x4009: reserved space, nothing of consequence stored here
> x400A: 0100 0000 0000 0111
> 
> When the program executes, it would store the value 0 into x4007 and 
> the value 1 into x4008.  Memory location x4009 would still be 
> unspecified when the program halts.
> 
> Hope this helps.
> Yale Patt