User manual

6 OnRISC Hardware API

6.6. I2C

I2C

(Inter-Integrated Circuit) is a multi-master serial computer bus. In the OnRISC integrated

I2C controller is already supported by the mainline kernel. A good starting point on how to use

I2C is the hwtest utility (see Section C.6). test_LCD() routine from hwtest/module_i2c.c shows

how to communicate with an I2C device. Additional information can be found in the Linux kernel

documentation Documentation/i2c. I2C platform device initialization is described in

Documentation/i2c/instantiating-devices.

6.7. WLAN Button (Alekto LAN Only)

OnRISC Alekto LAN provides an additional button. By default this button is used to control

WLAN card’s transmit power. This button is just connected to GPIO line and will be controlled

by wland service (refer to Section 4.1.3). To use it for other needs just disable the wland service.

Following ioctl command for /dev/gpio is provided to get button’s state:

GPIO_CMD_GET_BTN_WLAN

return value is 0 - for not pressed and 1 - for pressed.

6.8. Watchdog Timer

The OnRISC provides a watchdog timer

(WDT) that can work in intervals from 1 second to

maximal 171 seconds. The access to the WDT occurs via /dev/watchdog device. After starting

the WDT it should be turned oﬀ or reloaded after the critical part otherwise the system will reboot.

Table 6 shows the most important IOCTLs to control WDT.

IOCTL Description

WDIOC_SETTIMEOUT set timeout and start the timer

WDIOC_GETTIMEOUT get timeout

WDIOC_SETOPTIONS enable (WDIOS_ENABLECARD)

disable (WDIOS_DISABLECARD) the timer

WDIOC_KEEPALIVE reload the timer

Table 6: Watchdog Timer IOCTLs

The WDT driver provides a special option called "Disable watchdog shutdown on close" to prevent

stopping the timer on WDT descriptor close (see Figure 4). This is a compile-time option. It is

deactivated by default, so you have to build your own kernel if you need it.

See examples/wdtimer.c for WDT usage example.

http://en.wikipedia.org/wiki/I2C

For further information see drivers/watchdog/ks8695_wdt.c

May 2014 OnRISC User Manual 47