Parallel Streams Access - 2025.2 English - UG1079

AI Engine Kernel and Graph Programming Guide (UG1079)
Document ID
UG1079
Release Date
2025-11-26
Version
2025.2 English

The AI Engine can 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. See the following 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, you can use aie_stream_resource_out::a and aie_stream_resource_out::b to denote two parallel output streams.

Recommended: Use resource annotations consistently on the same stream. Otherwise, the compiler scheduling might not follow the desired order of accesses with different annotations.

For example, AMD does not recommend the following stream operations:

//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 annotation

Instead, use the following type of code:

//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