Analyze the following lines of code. Refer to Two's Complement and Fractional Arithmetic for 16-bit 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 = 3
5 ; AR0 = 1
6 ; AR2 = 1000h
7 ; AR3 = 1004h
8 ;
9 ; FRCT = 1
10
11 stl A,*AR3+%
12 rptz A,(FIR_len-1)
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, BK, AR0,
AR2, and AR3 before the execution of
the first instruction, stl. 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.
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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.
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When working through the exercise, take into account that the
accumulator A is a 40-bit 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. (Assume the multiplier is in
fractional arithmetic mode for all exercises, unless you are
told otherwise.) Therefore, 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 16-bit Processors.
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