| 99 | UART0_TXD | UART0_TXD | UART2_TX | GP32_UART2_TXD | unused_UART2_TX |
|---|---|---|---|---|---|
| 101 | UART0_RXD | UART0_RXD | UART2_RX | GP33_UART2_RXD | unused_UART2_RX |
我有一个困扰很久的问题想请教各位专家。按需求，我要将原先的uart0口变更配置，作为一个模拟i2c slave设备的出口，即UART0_TXD作为模拟I2C slave设备的SDA，UART0_RXD作为模拟I2C slave设备的SCL，我已经修改了pinmux配置(tegra234-mb1-bct-pinmux-p3767-dp-a03.dtsi)如下(，uart2_tx_px4和uart2_rx_px5的配置从pinmux_default: common中迁移到drive_default: drive中)：
drive_default: drive {
uart2_tx_px4 {
nvidia,pins = "uart2_tx_px4";
nvidia,function = "rsvd1";
nvidia,pull = <TEGRA_PIN_PULL_UP>;
nvidia,tristate = <TEGRA_PIN_DISABLE>;
nvidia,enable-input = <TEGRA_PIN_ENABLE>;
nvidia,open-drain = <TEGRA_PIN_ENABLE>;
nvidia,io-high-voltage = <TEGRA_PIN_DISABLE>;
nvidia,lpdr = <TEGRA_PIN_DISABLE>;
};
uart2_rx_px5 {
nvidia,pins = "uart2_rx_px5";
nvidia,function = "rsvd1";
nvidia,pull = <TEGRA_PIN_PULL_UP>;
nvidia,tristate = <TEGRA_PIN_DISABLE>;
nvidia,enable-input = <TEGRA_PIN_ENABLE>;
nvidia,open-drain = <TEGRA_PIN_ENABLE>;
nvidia,io-high-voltage = <TEGRA_PIN_DISABLE>;
nvidia,lpdr = <TEGRA_PIN_DISABLE>;
};
};
并在tegra234-mb1-bct-gpio-p3767-dp-a03.dtsi中的gpio-input和gpio-output-high配置中新增了TEGRA234_MAIN_GPIO(X, 4)和TEGRA234_MAIN_GPIO(X, 5)。进入系统后，查询相关配置寄存器的值=如下：
root@localhost:/mnt/appdata/i2c_slave# busybox devmem 0x0243d050
0x00000049
root@localhost:/mnt/appdata/i2c_slave# busybox devmem 0x0243d058
0x00000049
但问题在于我每次加载I2C slave驱动代码后，SDA即变为默认低电平，但SCL保持高电平，即
gpio-466 (PX.04 |i2c-sda ) in lo
gpio-467 (PX.05 |i2c-scl ) in hi IRQ
驱动代码上对于GPIO的初始化是一致的，查看dmesg日志为：
[ 69.980206] I2C Slave driver initializing…
[ 69.980261] SDA before gpio_request: HI
[ 69.980266] SCL before gpio_request: HI
[ 69.980345] SDA after gpio_request: HI
[ 69.980371] SDA after gpio_direction_input: LO
[ 69.980392] SCL after gpio_request: HI
[ 69.980410] SCL after gpio_direction_input: HI
[ 69.980547] irq: IRQ310: trimming hierarchy from :pmc@c360000
[ 69.980645] I2C Slave driver loaded (SDA:466, SCL:467)
此后SDA一直保持为低电平。事实上，如果我不在tegra234-mb1-bct-gpio-p3767-dp-a03.dtsi中设置默认值，则SDA会一直保持为低电平
这可能是什么原因导致的呢，因为我在系统中，加载驱动前一直都是可以通过echo 466 > /sys/class/gpio/export这样的系统命令配置输出高低电平的，且万用电表测量电压3.3V。但为什么系统为什么会设置SDA的默认电平为低呢，我还有什么地方需要修改呢？谢谢
gpio-466 (PX.04 |sysfs ) out hi