Finite Impulse Response Filters - Digital Signal Processing and Applications with the C6713 and C6416 DSK - page 173

/* FIRcirc_ext.cmd Linker command file for external memory*/

MEMORY
{
IVECS: org = 0h, len = 0x220
IRAM: org = 0x00000220, len = 0x0002FFFF
SRAM_EXT1: org = 0x80000000, len = 0x00000110
SRAM_EXT2: org = 0x80000110, len = 0x00100000
FLASH: org = 0x90000000, len = 0x00020000
}

SECTIONS
{
circdata :> SRAM_EXT1 /*buffer in external mem*/
.vecs :> IVECS /*Created in vectors file*/

.text :> IRAM /*Created by C Compiler*/

.bss :> IRAM
.cinit :> IRAM
.stack :> IRAM
.sysmem :> IRAM
.const :> IRAM
.switch :> IRAM
.far :> IRAM
.cio :> IRAM
.csldata :> IRAM
}

FIGURE 4.37. Linker command file for a circular buffer in external memory
( FIRcirc_ext.cmd ).

4.8 ASSIGNMENTS

1. (a) Design a 65-coefficient FIR lowpass filter with a cutoff frequency of
2500 Hz and a sampling frequency of 8 kHz. Implement it in real time using
the Hamming window function.
(b) Compare the filter's characteristics between the Hamming, Hanning, and
Kaiser windows.
2. The coefficient file LP1500_256.cof (in the folder FIR ) represents 256
coefficients of an FIR lowpass filter, with a bandwidth of 1500 Hz, when sam-
pling at 48 kHz. Implement this filter to achieve this 1500-Hz bandwidth. Hint:
the C-coded examples in this chapter may not be efficient enough to imple-
ment this filter at a sampling rate of 48 kHz (what about an ASM-coded FIR
function with a circular buffer to update the delays?).
3. Design and implement a multiband FIR filter with two passbands, one
centered at 2500 and the other at 3500 Hz. Select a sampling frequency of
16 kHz.