Finite Impulse Response Filters - Digital Signal Processing and Applications with the C6713 and C6416 DSK - page 170

FIGURE 4.36. Frequency characteristics of a 128-coefficient FIR bandpass filter centered at
1750 Hz using MATLAB's filter designer SPTool described in Appendix D.

Within a C program, an inline assembly code can be used with the asm state-
ment. For example,

asm(“ MVK 0x0040,B6”)

Note the blank space after the first quotation mark so that the instruction does not
start in column 1. The circular mode of addressing eliminates the data move to
update the delay samples, since a pointer can be moved to achieve the same results
and much faster. Initially, the register pointer A7 points to the last address in the
sample buffer. Consider for now the sample buffer only, since it is circular. (Note
that the coefficient's buffer is not made to be circular.)

1. Time n. At time n , A7 points to the end of the buffer, where the newest sample
is stored. It is then postincremented to point to the beginning of the buffer,
as shown in Table 4.4. Then the section of code within the loop starts and
calculates

() =- ( ) ( ( ) ) +- ( ) ( ( ) ) +◊◊◊+ () ( )

yn hN 1 xn -- N 1 hN 2 xn -- N 2 h 1 xn - 1

()()

+ hxn 0