今天上班写了个小代码，用于检测掉电处理。当主控CPU的GPIO_7_11被拉低的时候，则触发中断，表明发生了外部掉电事件。
其原理图如下：
一个三极管，左边是一个外部信号，当POW_SW为高的时候，表明IMX CPU外部供电断开了。此时PMIC自动切换到电池供电。
就这个NPN型的三极管而言，POW_SW高，三极管的基极高，基极和发射极导通，集电极和发射极也导通，IMX端GPIO_7_11被拉低。
为了确保这个过程顺利执行，在GPIO被设置为中断腿之前，要设置为输入上拉（集电极读入为高）。如下是整个代码：
/*
* Author: King
* Date: 2016.8.8
*/
#include <linux/module.h>
#include <linux/device.h>
#include <linux/fs.h>
#include <linux/miscdevice.h>
#include <linux/sched.h>
#include <linux/wait.h>
#include <linux/irqreturn.h>
#include <linux/interrupt.h>
#include <asm/uaccess.h>
#include <mach/gpio.h>
#include <mach/iomux-v3.h>
#include <mach/iomux-mx6dl.h>
#define DEV_NAME "pmu"
#define VPU_POW_INT_PIN IMX_GPIO_NR(7, 11)
#define VPU_POW_INT gpio_to_irq(VPU_POW_INT_PIN)
#define EVENT_POW_OFF "EVENT_CHARGE_OFF\n"
MODULE_LICENSE("GPL");
MODULE_AUTHOR("king");
MODULE_DESCRIPTION("ywwh vpu pow detect");
static DECLARE_WAIT_QUEUE_HEAD(vpu_pow_read_wait);
static int wait_flag = 0;
ssize_t ywwh_vpu_pow_read(struct file *filp, char __user *buf,
size_t count, loff_t *ppos)
{
wait_event_interruptible(vpu_pow_read_wait, wait_flag);
wait_flag = 0;
if (copy_to_user(buf, EVENT_POW_OFF, strlen(EVENT_POW_OFF)))
return -EFAULT;
return strlen(EVENT_POW_OFF);
}
static struct file_operations ywwh_vpu_pow_ops = {
.owner = THIS_MODULE,
.read = ywwh_vpu_pow_read,
};
static struct miscdevice miscdev = {
.minor = MISC_DYNAMIC_MINOR,
.name = DEV_NAME,
.fops = &ywwh_vpu_pow_ops,
.nodename = DEV_NAME,
};
static irqreturn_t vpu_pow_off_irq(int irq, void *dev_id)
{
printk("interrupt happend!\n");
wake_up(&vpu_pow_read_wait);
wait_flag = 1;
return IRQ_HANDLED;
}
static int vpu_pow_init(void)
{
printk("irq = %u\n", VPU_POW_INT);
mxc_iomux_v3_setup_pad(MX6DL_PAD_GPIO_16__GPIO_7_11);
gpio_request(VPU_POW_INT_PIN, "vpu_pow_int");
gpio_direction_input(VPU_POW_INT_PIN);
printk("Get gpio val = %u\n", gpio_get_value_cansleep(VPU_POW_INT_PIN));
gpio_free(VPU_POW_INT_PIN);
int ret = request_irq(VPU_POW_INT, vpu_pow_off_irq,
IRQF_TRIGGER_FALLING, "vpu_pow_off_irq", NULL);
if (ret)
return ret;
ret = misc_register(&miscdev);
if (ret)
return ret;
return 0;
}
static void vpu_pow_exit(void)
{
misc_deregister(&miscdev);
}
module_init(vpu_pow_init);
module_exit(vpu_pow_exit);