diff --git a/boards/uniboard1/designs/unb1_test/tb/python/tc_unb1_test.py b/boards/uniboard1/designs/unb1_test/tb/python/tc_unb1_test.py
index b38448c17a125a1f4db6dbe2bc1efd436d9a41d2..f343efe7a2a637d2f335f9aabd6b846a24c25695 100644
--- a/boards/uniboard1/designs/unb1_test/tb/python/tc_unb1_test.py
+++ b/boards/uniboard1/designs/unb1_test/tb/python/tc_unb1_test.py
@@ -83,8 +83,14 @@ def test_bg(tc, io):
 
     settings = Bg.read_block_gen_settings()
     samples_per_packet = settings[0][1]
+    gapsize            = settings[0][3]
+    blocksize          = pow(2, ceil_log2(samples_per_packet+gapsize))
+
+    Bg = pi_diag_block_gen.PiDiagBlockGen(tc,io,nofChannels=nof_streams, ramSizePerChannel=blocksize)
+    Db = pi_diag_data_buffer.PiDiagDataBuffer(tc,io,nofStreams=nof_streams,ramSizePerStream=blocksize)
+    resetptrn = [7]*samples_per_packet + [0]*(blocksize-samples_per_packet)
+    Db.overwrite_all_data_buffers(resetptrn, vLevel=9)
 
-    Bg = pi_diag_block_gen.PiDiagBlockGen(tc,io,nofChannels=nof_streams, ramSizePerChannel=samples_per_packet)
     Bg.write_enable()  # or Bg.write_enable_pps()
     ppsh.wait_until_pps(vLevel=6)
 
@@ -95,14 +101,11 @@ def test_bg(tc, io):
         for r in ram: lram.append(list(r)) # () -> []
         bg_ram.append(lram)
 
-    #print 'bg_ram=',bg_ram
     #bg_ram[0][0]=0
 
-    Db = pi_diag_data_buffer.PiDiagDataBuffer(tc,io,nofStreams=nof_streams,ramSizePerStream=samples_per_packet)
     db_ram = []
     for s in range(nof_streams):
         db_ram.append(Db.read_data_buffer(streamNr=s,vLevel=5))
-    #print 'db_ram=',db_ram
 
     tc.set_section_id('Compare (BG==DB) - ')
     compared = (bg_ram == db_ram)