MAX_BUFFER_SIZE
size_t bufferLength = min_c(MAX_BUFFER_SIZE, length);
unsigned char data3[MAX_BUFFER_SIZE];
ret = bulk_in->BulkTransfer(data3, MAX_BUFFER_SIZE);
ret = bulk_in->BulkTransfer(&frame[offset], MAX_BUFFER_SIZE);
if (ret != MAX_BUFFER_SIZE) // not a full buffer, must be end of frame