3.6.6.3 Pragmas

A global constraint of operation resources can be set via 3.6.2.2.8 set_resource_constraint; constraining the operation resource within a function, a loop or a block of code is not yet available.

Functions that are not inlined (automatically by SmartHLS tool or specified via the 3.6.1.5 Inline Function pragma) always have a single RTL module instance in hardware, and it is shared by all callers. Replication of a function instance in hardware can be achieved by the 3.6.1.7 Replicate Function and 3.6.1.5 Inline Function pragmas. In the case of multi-threading, each thread of a function creates an instance of the corresponding RTL module.

See the 3.6.1.23 Partition Top-Level Interface and 3.6.1.22 Partition Memory pragmas.

If the variable is globally/locally declared variable, move the pragma to right before the variable declaration.

If the variable is a top-level function argument, add the pragma to the beginning of the function definition block.

Example:

VHLS: #pragma HLS array_partition variable=<VAR> <TYPE> dim=<DIM>

If <VAR> is a global/local declared variable, use #pragma HLS memory partition variable(<VAR>) type(<TYPE>) dim(<DIM>) + move it to right before the <VAR> variable declaration.

If <VAR> is a top-level function argument, use #pragma HLS memory partition argument(<VAR>) type(<TYPE>) dim(<DIM>) + add it add the beginning of the function definition block.

SmartHLS supports complete memory partitioning in either 1 or all dimensions, while Vitis HLS can apply complete memory partitioning in more than 1 discrete dimensions. To port such case, users may need to reshape the array. Below is an example.

VHLS:

ap_uint<12> buffer[DIM_X][DIM_Y][DIM_Z];
#pragma HLS_ARRAY_PARTITION variable=buffer complete dim=1
#pragma HLS_ARRAY_PARTITION variable=buffer complete dim=2
// Access macro of 'buffer'
#define BUFFER(x,y,z)  (buffer[x][y][z])

#pragma HLS memory partition variable(buffer) type(complete) dim(1)
ap_uint<12> buffer[DIM_X*DIM_Y][DIM_Z];
// Access macro of 'buffer'
#define BUFFER(x,y,z)  (buffer[(x)*DIM_Y+(y)][z])

See the 3.6.1.4 Bound Loop pragma, and lift it out of the loop. Note that SmartHLS does not capture the average number of loop iterations.

Example:

VHLS: #pragma HLS loop_tripcount min=<MIN> max=<MAX> avg=<AVG>

SHLS: #pragma HLS loop bounds lower(<MIN>) upper(<MAX>) + lift outside the loop

See 3.6.1.10 Pipeline Function and 3.6.1.2 Pipeline Loop pragmas.

If inside a loop, the pragma should be lifted outside the loop.

If inside a function, add the pragma to the beginning of the function definition block.