The AI Engine is able to use two streaming inputs or two streaming outputs in parallel.
To guide the tool to use parallel streams, use
aie_stream_resource_in and aie_stream_resource_out annotations with different enumeration values, like
aie_stream_resource_in::a and aie_stream_resource_in::b for input streams. For
example:void vect_mul(input_stream<int8>* __restrict data1, input_stream<int8>* __restrict data2,
output_stream<int8>* __restrict out){
while(true)
chess_prepare_for_pipelining
chess_loop_range(8,)
{
aie::vector<int8,16> va_int8=readincr_v<16,aie_stream_resource_in::a>(data1);
aie::vector<int8,16> vb_int8=readincr_v<16,aie_stream_resource_in::b>(data2);
auto vc=aie::mul(va_int8,vb_int8);
// Avoid the write instruction to occur at the same cycle as the readincr of data1
writeincr<aie_stream_resource_out::a>(out,vc.to_vector<int8>(0));
va_int8=readincr_v<16,aie_stream_resource_in::a>(data1);
vb_int8=readincr_v<16,aie_stream_resource_in::b>(data2);
vc=aie::mul(va_int8,vb_int8);
// This writeincr can be scheduled as soon as possible
// as there is the __restrict keyword in function signature
writeincr(out,vc.to_vector<int8>(0));
}
}Similarly, aie_stream_resource_out::a and
aie_stream_resource_out::b can be used to denote two
parallel output streams.
Recommended: When resource annotations are used on streams,
use the annotation consistently on the same stream. Otherwise, the compiler scheduling may
not follow the desired order of accesses with different annotations.
For example, the following stream operations are not recommended:
//input_stream<int32> * __restrict sin
......
int32 a = readincr(sin); //access stream with none annotation
int32 b = readincr(sin);
v4int32 c_vect = readincr_v<4, aie_stream_resource_in::a>(sin); //access stream with different annotationInstead, the following type of code can be used:
//input_stream<int32> * __restrict sin
......
int32 a = readincr<aie_stream_resource_in::a>(sin); //access stream with annotation
int32 b = readincr<aie_stream_resource_in::a>(sin);
v4int32 c_vect = readincr_v<4, aie_stream_resource_in::a>(sin); //access stream with the same annotation