官方文档说
BOOL SetupComm(
HANDLE hFile,
DWORD dwInQueue,
DWORD dwOutQueue
);
dwInQueue
[in] Specifies the recommended size, in bytes, of the device's internal input buffer.
dwOutQueue
[in] Specifies the recommended size, in bytes, of the device's internal output buffer.
The dwInQueue and dwOutQueue parameters specify the recommended sizes for the internal buffers used by the driver for the specified device
也就是和设备底层驱动有关的输入输出缓冲区
和readfile的缓冲区是不一样的