Intel Extensible Firmware Interface Specification page 237

Description
The
SetAttributes()
out, parity, data bits, and stop bits on a serial device.
The controller for a serial device is programmed with the specified attributes. If the Parity,
DataBits, or
StopBits
is below the minimum baud rate supported by the serial device, an error will be
BaudRate
returned. The nearest baud rate supported by the serial device will be selected without exceeding
the parameter. If the specified
BaudRate
supported by the serial device, an error will be returned. The nearest FIFO size supported by the
serial device will be selected without exceeding the
Status Codes Returned
EFI_SUCCESS
EFI_INVALID_PARAMETER
EFI_DEVICE_ERROR
Version 1.02
function sets the baud rate, receive-FIFO depth, transmit/receive time
values are not valid, then an error will be returned. If the specified
ReceiveFifoDepth
ReceiveFifoDepth
The new attributes were set on the serial device.
One or more of the attributes has an unsupported value.
The serial device is not functioning correctly.
12/12/00
Serial I/O Protocol
is below the smallest FIFO size
parameter.
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