diff --git a/core-buffer/include/FastH5Writer.hpp b/core-buffer/include/FastH5Writer.hpp
index 67249ba..6963e5c 100644
--- a/core-buffer/include/FastH5Writer.hpp
+++ b/core-buffer/include/FastH5Writer.hpp
@@ -6,7 +6,6 @@
 #include <string>
 #include <H5Cpp.h>
 
-template <class B>
 class FastH5Writer {
 
     const uint16_t CHUNKING_FACTOR = 1;
@@ -14,11 +13,13 @@ class FastH5Writer {
     const size_t n_frames_per_file_;
     const uint16_t y_frame_size_;
     const uint16_t x_frame_size_;
+    const size_t frame_bytes_size_;
 
     std::string current_output_filename_;
     H5::H5File current_output_file_;
     H5::DataSet current_image_dataset_;
     uint64_t current_pulse_id_;
+    size_t current_frame_index_;
 
     void create_image_dataset();
 
diff --git a/core-buffer/src/FastH5Writer.cpp b/core-buffer/src/FastH5Writer.cpp
index 4045ca2..c0dea2f 100644
--- a/core-buffer/src/FastH5Writer.cpp
+++ b/core-buffer/src/FastH5Writer.cpp
@@ -1,14 +1,24 @@
+#include <BufferUtils.hpp>
 #include "FastH5Writer.hpp"
+#include "date.h"
+#include <chrono>
+#include <sstream>
 
+extern "C"
+{
+    #include "H5DOpublic.h"
+}
 
-template<>
-FastH5Writer<uint16_t>::FastH5Writer(
+using namespace std;
+
+FastH5Writer::FastH5Writer(
         const size_t n_frames_per_file,
         const uint16_t y_frame_size,
         const uint16_t x_frame_size) :
             n_frames_per_file_(n_frames_per_file),
             y_frame_size_(y_frame_size),
             x_frame_size_(y_frame_size),
+            frame_bytes_size_(2 * y_frame_size * y_frame_size),
             current_output_filename_(""),
             current_output_file_(),
             current_image_dataset_(),
@@ -19,8 +29,7 @@ FastH5Writer<uint16_t>::FastH5Writer(
 //    auto file = H5::H5File(target_filename.c_str(), H5F_ACC_TRUNC);
 }
 
-template <class B>
-void FastH5Writer<B>::create_image_dataset()
+void FastH5Writer::create_image_dataset()
 {
     hsize_t dataset_dimension[3]  =
             {n_frames_per_file_, y_frame_size_, x_frame_size_};
@@ -41,14 +50,34 @@ void FastH5Writer<B>::create_image_dataset()
             "image", dataset_data_type, dataspace, dataset_properties);
 }
 
-template <class B>
-void FastH5Writer<B>::set_pulse_id(const uint64_t pulse_id)
+void FastH5Writer::set_pulse_id(const uint64_t pulse_id)
 {
     current_pulse_id_ = pulse_id;
+    current_frame_index_ = BufferUtils::get_file_frame_index(pulse_id);
 }
 
-template <class B>
-void FastH5Writer<B>::write_data(const char *buffer)
+void FastH5Writer::write_data(const char *buffer)
 {
-    
+        hsize_t offset[3] = {current_frame_index_, 0, 0};
+
+        if(H5DOwrite_chunk(
+                current_image_dataset_.getId(),
+                H5P_DEFAULT,
+                0, // Filters
+                offset, // Offset
+                frame_bytes_size_,
+                buffer))
+        {
+            stringstream err_msg;
+
+            using namespace date;
+            using namespace chrono;
+            err_msg << "[" << system_clock::now() << "]";
+            err_msg << "[FastH5Writer::write_data]";
+            // TODO: This error message is bad. Extract the real error from lib.
+            err_msg << " Error when writing to ";
+            err_msg << current_output_filename_;
+
+            throw runtime_error(err_msg.str());
+        }
 }
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