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usb/cdc: writing small blocks should not require allocation #991

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usb/cdc: writing small blocks should not require allocation #991

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7 changes: 4 additions & 3 deletions micropython/usb/usb-device-cdc/usb/device/cdc.py
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Original file line number Diff line number Diff line change
Expand Up @@ -350,10 +350,9 @@ def _rd_cb(self, ep, res, num_bytes):
###

def write(self, buf):
# use a memoryview to track how much of 'buf' we've written so far
# (unfortunately, this means a 1 block allocation for each write, but it's otherwise allocation free.)
start = time.ticks_ms()
mv = memoryview(buf)
# use a memoryview to track partial writes
mv = buf
while True:
# Keep pushing buf into _wb into it's all gone
nbytes = self._wb.write(mv)
Expand All @@ -362,6 +361,8 @@ def write(self, buf):
if nbytes == len(mv):
return len(buf) # Success

if mv is buf:
mv = memoryview(buf)
mv = mv[nbytes:]

# check for timeout
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