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In order to prevent UART data loss while asleep we recommend that flow control lines (RTS and CTS) are used to allow the chip to wake up and assert clear to send prior to transmission.
This is specifically suited for the case of an HCI UART device attempting to send data to its host CPU.
BTW, Should we don't use flow control lines to do this thing? just only use Uart TX and RX. The hardware also disable flow control lines on the host board.