tb: axis_replay_buffer: Allow delaying the last byte

Allow delaying the last byte to make it easier to exactly time when the
MAC sees the byte. This way, we can test to ensure that everything works
even when valid is only high for one cycle. We can't change signals
once valid goes high, so this is the only way to ensure this kind of
timing.

Signed-off-by: Sean Anderson <seanga2@gmail.com>

tb/axis_replay_buffer.py

@@ -10,8 +10,10 @@ from .util import ClockEnable, lookahead, timeout
 
 BUF_SIZE = 54
 
-async def send_packet(signals, packet, ratio=1):
+async def send_packet(signals, packet, ratio=1, last_extra=0):
     for val, last in lookahead(packet):
+        if last and last_extra:
+            await ClockCycles(signals['clk'], last_extra, rising=False)
         if 'err' in signals:
             if val is None:
                 signals['data'].value = 0