Device driver function 07h      Input Flush                 C

    Input Flush terminates any read operations in progress and empties
    the device input 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.