首页 / 操作系统 / Linux / 为OpenWrt添加实时钟（RTC）--以MT7620为例

前言

实时钟,英文名RTC（Real Time Clock）,在PC里面很常见,在OpenWrt里面却鲜有提及,手头上有一个DS1307的TinyRTC实时钟模块,经过一番折腾,将其融合到了OpenWrt系统,遂将操作过程记录成文. 

背景知识

DS1307在最新的OpenWrt中已经提供支持,却没有整合进ramips中,因此,本文的一个重点便是如何为ramips系统配置ds1307.另外,为ds1307编写合适的dts节点也是本文的一个重点. 

实现过程

1.为ramips配置ds1307支持

系统在./scripts/medatata.pl中判断并处理RTC_SUPPORT开关,分析之后,原来是在 target/linux/ramips/mt7620/target.mk中,将原始的内容:FEATURES+=usb修改为:FEATURES+=usb rtc即可打开mt7620对rtc的支持.此时,make kernel_menuconfig进入配置菜单.同时应注意,由于ds1307是i2c接口的模块,因此,在device中需要配置i2c的支持.选中i2c之后,便可以在Device Drivers -> Real Time Clock中看到ds1307  .config - Linux/mips 3.14.28 Kernel Configuration > Device Drivers > Real Time Clock ─────────────────────────────────────┌──── Dallas/Maxim DS1307/37/38/39/40, ST M41T00, EPSON RX-8025 ────┐│ CONFIG_RTC_DRV_DS1307:││ ││ If you say yes here you get support for various compatible RTC││ chips （often with battery backup） connected with I2C. This driver ││ should handle DS1307, DS1337, DS1338, DS1339, DS1340, ST M41T00,││ EPSON RX-8025 and probably other chips. In some cases the RTC ││ must already have been initialized （by manufacturing or a ││ bootloader）.││ ││ The first seven registers on these chips hold an RTC, and other ││ registers may add features such as NVRAM, a trickle charger for ││ the RTC/NVRAM backup power, and alarms. NVRAM is visible in ││ sysfs, but other chip features may not be available.││ ││ This driver can also be built as a module. If so, the module││ will be called rtc-ds1307.││ ││ Symbol: RTC_DRV_DS1307 [=y] ││ Type: tristate││ Prompt: Dallas/Maxim DS1307/37/38/39/40, ST M41T00, EPSON RX-8025 ││ Location: ││ -> Device Drivers ││ -> Real Time Clock （RTC_CLASS [=y]） ││ Defined at drivers/rtc/Kconfig:166││ Depends on: RTC_CLASS [=y] && I2C [=y]││ ││ ││ │├───────────────────────────────────────────────────────────（100%）──┤│ < Exit >│└───────────────────────────────────────────────────────────────────┘

2.为ds1307建立dts节点

配置好ds1307的编译开关后,接下来的工作就要在dts里面添加ds1307的设备节点.查阅ds1307的资料,其配置的i2c地址为0x68,因此,dts中可以添加如下内容: i2c@0 { compatible = "i2c-gpio";gpios = <&gpio2 0 0 /* sda = wan_led*/ &gpio3 0 0 /* scl = wlan_led*/ >; i2c-gpio,delay-us = <10>;/* ~20 kHz */#address-cells = <1>;#size-cells = <0>;rtc@68 { compatible = "dallas,ds1307";reg = <0x68>; }; }; 完成这两步后,就可以make出支持ds1307的固件. 系统启动时,可以在TTL中看到如下内容: [0.130000] i2c-gpio i2c.4: using pins 40 （SDA） and 72 （SCL）...[0.790000] rtc-ds1307 0-0068: rtc core: registered ds1307 as rtc0[0.810000] rtc-ds1307 0-0068: 56 bytes nvram...[0.810000] rtc-ds1307 0-0068: setting system clock to 2015-01-26 22:31:15 UTC （1422311475）
说明RTC已经成功的整合到了mt7620的系统中. ps:系统自带的hwclock命令可以很方便的对RTC进行相应的操作.

后记

kernel 3.14.28中的i2c-ralink驱动已经能够正常驱动7620的硬件i2c,只是在用i2cdetect的时候,需要加上-r参数,这样才能正确probe到设备.OpenWrt：Ubuntu 12.04搭建OpenWrt编译环境 http://www.linuxidc.com/Linux/2016-07/133764.htm本文永久更新链接地址：http://www.linuxidc.com/Linux/2016-10/136256.htm