Device driver function 0Bh      Output Flush                C

    Output Flush terminates any write operations in progress and
    empties the device output buffer.

    This function is required for character device drivers only.

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    frStatus
    Specifies the status of the completed function. If the function
    was successful, the driver must set the done bit (bit 8).
    Otherwise, the driver must set both the error and done bits (bits
    15 and 8) and copy an error value to the low-order byte.