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Then, the first address of the reserved 128 bytes is at the
word boundary in memory, that is the 2 LSBs of the address (inbinary) are 0. Similarly, for half-word alignment, you should
have
.align directive to do this. For
example, if you have
1 .align 2
2 buffer .space 1283 ...
The
.include directive is used to read
the source lines from another file. If you have
1 .include ``other.asm''
will input the lines in
other.asm at this
location. This is useful when working with multiple files.Instead of making a project having multiple files, you can
simply include these different files in one file.
Other assembler directives include
.end ,
.macro, .endm later.
How do you write comments in your assembly program? Anything
that follows
; is considered as a comment
and ignored by the assembler. For example,
1 ; this is a comment
2 ADD .L1 A1,A2,A3 ;add a1 and a2
Each instruction has particular functional units that can execute it. For a complete list of the instructions that can beexecuted in each functional unit, see Table 3-2 in the instruction set manual. Note that some instructions can beexecuted by several different functional units.
shows how data and
addresses can be transfered between the registers, functionalunits and the external memory. If you observe carefully, the
destination path (marked as
dst ) going
out of the
.L1, .S1, .M1 and
D1 units are connected to the register
file A.
.L2, .S2, .M2 and
D2 units should be used.
Therefore if you know the instruction and the destination register, you should be able to assign the functional unit toit.
(Functional units): List all the functional units you can assign to each of these instructions:
ADD .?? A0,A1,A2 B .?? A1 MVKL .?? 000023feh, B0 LDW .?? *A10, A3 Intentionally left blank.
If you look at again, each functional unit must receive one of the source data from thecorresponding register file.For example, look at the following assembly instruction:
1 ADD .L1 A0,B0,A1
The
.L1 unit gets data from
A0 (this is natural) and
B0 (this is not) and stores the result in
A1 (this is a must). The data path
through which the content of
B0 is
conveyed to the
.L1 unit is called
1X
cross path . When this
happens, we add
x to the functional unit
to designate the cross path:
1 ADD .L1x A0,B0,A1
Similarly the data path from register file
B to the
.M2, .S2 and
.L2 units are called
2X cross path.
(Cross path): List all the functional units that can be assigned to each of the instruction:
ADD .??? B0,A1,B2 MPY .??? A1,B2,A4 Intentionally left blank.
In fact, when you write an assembly program, you can omit the functional unit assignment altogether. The assembler figuresout the available functional units and properly assigns them. However, manually assigned functional units help you to figureout where the actual execution takes place and how the data move around between register files and functional units. Thisis particularly useful when you put multiple instructions in parallel. We will learn about the parallel instructions lateron.
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