Intel Extensible Firmware Interface User Manual
Page 351
Protocols
— Console Support
Version 1.10
12/01/02
10-57
//*******************************************************
// EFI_PARITY_TYPE
//*******************************************************
typedef enum {
DefaultParity,
NoParity,
EvenParity,
OddParity,
MarkParity,
SpaceParity
} EFI_PARITY_TYPE;
//*******************************************************
// EFI_STOP_BITS_TYPE
//*******************************************************
typedef enum {
DefaultStopBits,
OneStopBit,
// 1 stop bit
OneFiveStopBits,
// 1.5 stop bits
TwoStopBits
// 2 stop bits
} EFI_STOP_BITS_TYPE;
Description
The Serial I/O protocol is used to communicate with UART-style serial devices. These can be
standard UART serial ports in PC-AT systems, serial ports attached to a USB interface, or
potentially any character-based I/O device.
The Serial I/O protocol can control byte I/O style devices from a generic device to a device with
features such as a UART. As such many of the serial I/O features are optional to allow for the case
of devices that do not have UART controls. Each of these options is called out in the specific serial
I/O functions.
The default attributes for all UART-style serial device interfaces are: 115,200 baud, a 1 byte
receive FIFO, a 1,000,000 microsecond timeout per character, no parity, 8 data bits, and 1 stop bit.
Flow control is the responsibility of the software that uses the protocol. Hardware flow control can
be implemented through the use of the
functions
(described below) to monitor and assert the flow control signals. The XON/XOFF flow control
algorithm can be implemented in software by inserting XON and XOFF characters into the serial
data stream as required.
Special care must be taken if a significant amount of data is going to be read from a serial device.
Since EFI drivers are polled mode drivers, characters received on a serial device might be missed.
It is the responsibility of the software that uses the protocol to check for new data often enough to
guarantee that no characters will be missed. The required polling frequency depends on the baud
rate of the connection and the depth of the receive FIFO.