Quartus custom Stream & distinction between g++ (nnet::stream) and i++ (ihc::stream)

Author: bo3z

hls4ml/templates/quartus/ac_types/stream.h

@@ -0,0 +1,36 @@
+#ifndef NNET_STREAM_H
+#define NNET_STREAM_H
+
+#include <deque>
+
+namespace nnet {
+
+/*
+* A struct with the same high-level functionality as Intel's HLS ihc::stream
+* This struct is used during GCC compilation / hls4ml model.predict(...)
+* This is because GCC does not have access to HLS source files (ihc::stream)
+* Software-wise, this struct behaves like a first-in, first-out (FIFO) buffer
+* However, it cannot be used for HLS synthesis, since it uses dynamic memory allocation (deque)
+*/
+template<typename T>
+struct stream {
+  private:
+    std::deque<T> _data;
+
+  public:
+    stream() {}
+
+    T read() {
+        T element = _data.front();
+        _data.pop_front();
+        return element; 
+    }
+
+    void write(const T& element) { 
+        _data.push_back(element);
+    }   
+};
+
+}
+ 
+#endif

hls4ml/templates/quartus/firmware/defines.h

@@ -1,14 +1,42 @@
 #ifndef DEFINES_H_
 #define DEFINES_H_
 
+/*
+* Intel HLS makes use of three streaming interfaces:
+*   (1) stream_in - used as the main input to a component
+*   (2) stream_out - used as the main output of a component
+*   (3) stream - allows both reading and writing; used for inter-component connections
+* ihc::stream has a implicitly deleted constructor and therefore, cannot be used as the output of a function/component
+* Therefore, variables of type 'stream' are always passed by reference
+*/
+
 #ifndef __INTELFPGA_COMPILER__
+
 #include "ac_int.h"
 #include "ac_fixed.h"
 #define hls_register
+
+#include "stream.h"
+template<typename T>
+using stream = nnet::stream<T>;
+template<typename T>
+using stream_in = nnet::stream<T>;
+template<typename T>
+using stream_out = nnet::stream<T>;
+
 #else
+
 #include "HLS/hls.h"
 #include "HLS/ac_int.h"
 #include "HLS/ac_fixed.h"
+
+template<typename T>
+using stream = ihc::stream<T>;
+template<typename T>
+using stream_in = ihc::stream_in<T>;
+template<typename T>
+using stream_out = ihc::stream_out<T>;
+
 #endif
 
 //hls-fpga-machine-learning insert numbers