Shift Register (OpenCL Kernel)¶
This example demonstrates how to shift values in registers in each clock cycle
KEY CONCEPTS: Kernel Optimization, Shift Register, FIR
KEYWORDS: xcl_array_partition, getProfilingInfo
This example demonstrates two ways to implement an FIR filter discrete convolution operation. It requires the values of all elements of FIR filter array for each element of the output array.
In the naive implementation, limited memory ports are available from the
shift_reg
array to the kernel interface thus efficient pipelining of
the operation is not possible.
int coeff_reg[N_COEFF];
__attribute__((xcl_loop_tripcount(c_n, c_n)))
read_coef: for (int i = 0 ; i < N_COEFF ; i++) coeff_reg[i] = coeff[i];
__attribute__((xcl_loop_tripcount(c_size, c_size)))
outer_loop:
for (int j = 0; j < signal_length; j++) {
int acc = 0;
shift_loop:
__attribute__((xcl_pipeline_loop(1)))
for (int i = min(j,N_COEFF-1); i >= 0; i--) {
acc += signal_r[j-i] * coeff_reg[i];
}
output_r[j] = acc;
}
In the fir_shift_register
attribute xcl_array_partition
is used
to provide all array values simultaneously by partitioning the array
such that each element has its own ports for read/write. Also, since
outer loop
uses attribute xcl_pipeline_loop
, Vivado HLS
compiler automatically applies loop unrolling
to the shift_loop
.
int shift_reg[N_COEFF] __attribute__((xcl_array_partition(complete, 0)));
__attribute__((xcl_loop_tripcount(c_n, c_n)))
init_loop:
for (int i = 0; i < N_COEFF; i++) {
shift_reg[i] = 0;
coeff_reg[i] = coeff[i];
}
outer_loop:
__attribute__((xcl_pipeline_loop(1)))
__attribute__((xcl_loop_tripcount(c_size, c_size)))
for(int j = 0; j < signal_length; j++) {
int acc = 0;
int x = signal_r[j];
__attribute__((xcl_loop_tripcount(c_n, c_n)))
shift_loop:
for (int i = N_COEFF-1; i >= 0; i--) {
if (i == 0) {
acc += x * coeff_reg[0];
shift_reg[0] = x;
} else {
shift_reg[i] = shift_reg[i-1];
acc += shift_reg[i] * coeff_reg[i];
}
}
output_r[j] = acc;
}
DESIGN FILES¶
Application code is located in the src directory. Accelerator binary files will be compiled to the xclbin directory. The xclbin directory is required by the Makefile and its contents will be filled during compilation. A listing of all the files in this example is shown below
src/fir.cl
src/host.cpp
COMMAND LINE ARGUMENTS¶
Once the environment has been configured, the application can be executed by
./shift_register <fir XCLBIN>