Analyze the following lines of code. Refer to Two's Complement and Fractional Arithmetic for 16bit Processors, Addressing Modes for TI TMS320C54x, and the Mnemonic Instruction Set [link] manual for help.
1 FIR_len .set 3
2
3 ; Assume:
4 ; BK = FIR_len
5 ; AR0 = 1
6 ; AR2 = 1000h
7 ; AR3 = 1004h
8 ;
9 ; FRCT = 1
10
11 stl A,*AR3+%
12 rptz A,(FIR_len1)
13 mac *AR2+0%,*AR3+0%,A
Anything following a ";
" is considered a comment.
In this case, the comments indicate the contents of the
auxiliary registers, the BK
register, and the address registers before the execution of
the first instruction, stl
.
The line FIR_len .set 3
defines the name FIR_len as equal to 3. The BK
register contains the length of the
circular buffer we want to use. The %
modifies the increment operator +
so that it
behaves as a circular buffer. This means that the address registers will be incremented until the
(memoryaddress mod valueinBK) = 0. When the increment operator +
is followed by a 0
,
it increments by the value specified in register AR0
.
Note that any number
followed by an "h
" or preceded with a
0x
represents a hexadecimal value.
Example 1
1000h and 0x1000 both refer to the decimal number 4096.
Assume that the data memory is initialized as follows starting
at location 1000h
.
After familiarizing yourself with the stl
,
rptz
, and mac
instructions, step
through each line of code and record the values of the
accumulator A
and auxiliary registers
AR2
and AR3
in the spaces provided
in Figure 2. Additionally, record the value
of the memory contents after all three instructions have been
"executed" in the blank data memory table provided in Figure 3.

When working through the exercise, take into account that the
accumulator A
is a 40bit register, and that the
multiplier is in the fractional arithmetic mode.
In this mode, integers on the DSP are interpreted as
fractions, and the multiplier will treat them accordingly.
This is done by shifting the result of the integer multiplier
in the ALU left one bit. (All the arithmetic is fractional in these examples.)
Multiplies performed by the ALU
(via the mac
instruction) produce a result that
is twice what you would expect if you just multiplied the two
integers together. DSP numerical representation and
arithmetic are described further in Two's Complement and Fractional Arithmetic
for 16bit Processors.
"Doug course at UIUC using the TI C54x DSP has been adopted by many EE, CE and CS depts Worldwide "