serialqueue: Limit message transmission to available receive buffer size

If the mcu is using a traditional serial port, then only send a new
message block if there is space available in the mcu receive buffer.
This should make it significantly less likely that high load on the
mcu will result in retransmits.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

klippy/serialhdl.py

@@ -90,6 +90,10 @@ class SerialReader:
             baud_adjust = self.BITS_PER_BYTE / mcu_baud
             self.ffi_lib.serialqueue_set_baud_adjust(
                 self.serialqueue, baud_adjust)
+        receive_window = msgparser.get_constant_int('RECEIVE_WINDOW', None)
+        if receive_window is not None:
+            self.ffi_lib.serialqueue_set_receive_window(
+                self.serialqueue, receive_window)
     def connect_file(self, debugoutput, dictionary, pace=False):
         self.ser = debugoutput
         self.msgparser.process_identify(dictionary, decompress=False)