Driver options: fast vs. small implementations, Ioctl() operations, Software files – Altera Embedded Peripherals IP User Manual
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Driver Options: Fast vs. Small Implementations
To accommodate the requirements of different types of systems, the JTAG UART driver has two variants,
a fast version and a small version. The fast behavior is used by default. Both the fast and small drivers fully
support the C standard library functions and the HAL API.
The fast driver is an interrupt-driven implementation, which allows the processor to perform other tasks
when the device is not ready to send or receive data. Because the JTAG UART data rate is slow compared
to the processor, the fast driver can provide a large performance benefit for systems that could be
performing other tasks in the interim. In addition, the fast version of the Altera Avalon JTAG UART
monitors the connection to the host. The driver discards characters if no host is connected, or if the host
is not running an application that handles the I/O stream.
The small driver is a polled implementation that waits for the JTAG UART hardware before sending and
receiving each character. The performance of the small driver is poor if you are sending large amounts of
data. The small version assumes that the host is always connected, and will never discard characters.
Therefore, the small driver will hang the system if the JTAG UART hardware is ever disconnected from
the host while the program is sending or receiving data. There are two ways to enable the small footprint
driver:
• Enable the small footprint setting for the HAL system library project. This option affects device drivers
for all devices in the system.
• Specify the preprocessor option
-DALTERA_AVALON_JTAG_UART_SMALL
. Use this option if you want the
small, polled implementation of the JTAG UART driver, but you do not want to affect the drivers for
other devices.
ioctl() Operations
The fast version of the JTAG UART driver supports the
ioctl()
function to allow HAL-based programs
to request device-specific operations. Specifically, you can use the
ioctl()
operations to control the
timeout period, and to detect whether or not a host is connected. The fast driver defines the
ioctl()
operations shown in below.
Table 7-3: JTAG UART ioctl() Operations for the Fast Driver Only
Request
Meaning
TIOCSTIMEOUT
Set the timeout (in seconds) after which the driver will decide that the host is
not connected. A timeout of 0 makes the target assume that the host is always
connected. The
ioctl
arg parameter passed in must be a pointer to an integer.
TIOCGCON-
NECTED
Sets the integer arg parameter to a value that indicates whether the host is
connected and acting as a terminal (1), or not connected (0). The
ioctl
arg
parameter passed in must be a pointer to an integer.
For details about the
ioctl()
function, refer to the Nios II Software Developer's Handbook.
Software Files
The JTAG UART core is accompanied by the following software files. These files define the low-level
interface to the hardware, and provide the HAL drivers. Application developers should not modify these
files.
7-8
Driver Options: Fast vs. Small Implementations
UG-01085
2014.24.07
Altera Corporation
JTAG UART Core