Linux红外驱动重点解析

飞奔的炮台

初次接触Linux内核，好仔细阅读顶层目录的readme文件，它是Linux内核的概述和编译命令说明。readme的说明侧重于X86等通用的平台，对于某些特殊的体系结构，可能有些特殊的说明。

红外遥控是我们经常见到的一种无线收发设备，比如电视遥控，空调遥控，现在电视遥控有些慢慢变成了蓝牙装置。昨天是在知识星球里面看到有人提问，今天来解析一份网友写的驱动程序。
调试红外需要注意几个细节
1、我们发射的遥控器用肉眼是看不到的，需要拿相机来观察。
2、红外接收管和普通的二极管不同，如果用错物料也是不行的。

1.NEC协议无线传输数据原理
NEC协议的特征：
1、8位地址和8位指令长度；
2、地址和命令两次传输；（确保可靠性）
3、PWM脉冲宽度调制，以发射红外载波的占空比代表“0”和“1”；
4、载波频率为38KHz
5、位时间为1.125ms和2.25ms
NEC码位的定义：一个脉冲对应560us的连续载波，一个逻辑1传输需要2.25ms（560us脉冲+1680us低电平），一个逻辑0的传输需要1.125ms（560us脉冲+560us低电平）。
而遥控接收头在收到脉冲时为低电平，在没有收到脉冲时为高电平，因此，我们在接收头端收到的信号为：逻辑1应该是560us低+1680us高，逻辑0应该是560us低+560us高。
如下图：

硬件

2. Linux下的驱动接收程序
参考原文：
https://blog.csdn.net/wllw7176/article/details/110506677
两个驱动文件

gpio-ir-recv.c
/* Copyright (c) 2012, Code Aurora Forum. All rights reserved.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 and
* only version 2 as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*/
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/interrupt.h>
#include <linux/gpio.h>
#include <linux/slab.h>
#include <linux/of.h>
#include <linux/of_gpio.h>
#include <linux/platform_device.h>
#include <linux/irq.h>
#include <media/rc-core.h>
#include <media/gpio-ir-recv.h>
#define GPIO_IR_DRIVER_NAME "gpio-rc-recv"
#define GPIO_IR_DEVICE_NAME "gpio_ir_recv"
struct gpio_rc_dev {
struct rc_dev *rcdev;
int gpio_nr;
bool active_low;
};
#ifdef CONFIG_OF
/*
* Translate OpenFirmware node properties into platform_data
*/
static int gpio_ir_recv_get_devtree_pdata(struct device *dev,
struct gpio_ir_recv_platform_data *pdata)
{
struct device_node *np = dev->of_node;
enum of_gpio_flags flags;
int gpio;
gpio = of_get_gpio_flags(np, 0, &flags);
if (gpio < 0) {
if (gpio != -EPROBE_DEFER)
dev_err(dev, "Failed to get gpio flags (%d)\n", gpio);
return gpio;
}
pdata->gpiogpio_nr = gpio;
pdata->active_low = (flags & OF_GPIO_ACTIVE_LOW);
/* probe() takes care of map_name == NULL or allowed_protos == 0 */
pdata->map_name = of_get_property(np, "linux,rc-map-name", NULL);
pdata->allowed_protos = 0;
return 0;
}
static const struct of_device_id gpio_ir_recv_of_match[] = {
{ .compatible = "gpio-ir-receiver", },
{ },
};
MODULE_DEVICE_TABLE(of, gpio_ir_recv_of_match);
#else /* !CONFIG_OF */
#define gpio_ir_recv_get_devtree_pdata(dev, pdata) (-ENOSYS)
#endif
static irqreturn_t gpio_ir_recv_irq(int irq, void *dev_id)
{
struct gpio_rc_dev *gpio_dev = dev_id;
int gval;
int rc = 0;
enum raw_event_type type = IR_SPACE;
gval = gpio_get_value(gpio_dev->gpio_nr);
if (gval < 0)
goto err_get_value;
if (gpio_dev->active_low)
gval = !gval;
if (gval == 1)
type = IR_PULSE;
rc = ir_raw_event_store_edge(gpio_dev->rcdev, type);
if (rc < 0)
goto err_get_value;
ir_raw_event_handle(gpio_dev->rcdev);
err_get_value:
return IRQ_HANDLED;
}
static int gpio_ir_recv_probe(struct platform_device *pdev)
{
struct gpio_rc_dev *gpio_dev;
struct rc_dev *rcdev;
const struct gpio_ir_recv_platform_data *pdata =
pdev->dev.platform_data;
int rc;
if (pdev->dev.of_node) {
struct gpio_ir_recv_platform_data *dtpdata =
devm_kzalloc(&pdev->dev, sizeof(*dtpdata), GFP_KERNEL);
if (!dtpdata)
return -ENOMEM;
rc = gpio_ir_recv_get_devtree_pdata(&pdev->dev, dtpdata);
if (rc)
return rc;
pdata = dtpdata;
}
if (!pdata)
return -EINVAL;
if (pdata->gpio_nr < 0)
return -EINVAL;
gpio_dev = kzalloc(sizeof(struct gpio_rc_dev), GFP_KERNEL);
if (!gpio_dev)
return -ENOMEM;
rcdev = rc_allocate_device();
if (!rcdev) {
rc = -ENOMEM;
goto err_allocate_device;
}
rcdev->priv = gpio_dev;
rcdev->driver_type = RC_DRIVER_IR_RAW;
rcdev->input_name = GPIO_IR_DEVICE_NAME;
rcdev->input_phys = GPIO_IR_DEVICE_NAME "/input0";
rcdev->input_id.bustype = BUS_HOST;
rcdev->input_id.vendor = 0x0001;
rcdev->input_id.product = 0x0001;
rcdev->input_id.version = 0x0100;
rcdev->dev.parent = &pdev->dev;
rcdev->driver_name = GPIO_IR_DRIVER_NAME;
if (pdata->allowed_protos)
rcdev->allowed_protocols = pdata->allowed_protos;
else
rcdev->allowed_protocols = RC_BIT_ALL;
rcdev->map_name = pdata->map_name ?: RC_MAP_EMPTY;
gpio_dev->rcdevrcdev = rcdev;
gpio_dev->gpio_nr = pdata->gpio_nr;
gpio_dev->active_low = pdata->active_low;
rc = gpio_request(pdata->gpio_nr, "gpio-ir-recv");
if (rc < 0)
goto err_gpio_request;
rc = gpio_direction_input(pdata->gpio_nr);
if (rc < 0)
goto err_gpio_direction_input;
rc = rc_register_device(rcdev);
if (rc < 0) {
dev_err(&pdev->dev, "failed to register rc device\n");
goto err_register_rc_device;
}
platform_set_drvdata(pdev, gpio_dev);
rc = request_any_context_irq(gpio_to_irq(pdata->gpio_nr),
gpio_ir_recv_irq,
IRQF_TRIGGER_FALLING | IRQF_TRIGGER_RISING,
"gpio-ir-recv-irq", gpio_dev);
if (rc < 0)
goto err_request_irq;
return 0;
err_request_irq:
rc_unregister_device(rcdev);
rcdev = NULL;
err_register_rc_device:
err_gpio_direction_input:
gpio_free(pdata->gpio_nr);
err_gpio_request:
rc_free_device(rcdev);
err_allocate_device:
kfree(gpio_dev);
return rc;
}
static int gpio_ir_recv_remove(struct platform_device *pdev)
{
struct gpio_rc_dev *gpio_dev = platform_get_drvdata(pdev);
free_irq(gpio_to_irq(gpio_dev->gpio_nr), gpio_dev);
rc_unregister_device(gpio_dev->rcdev);
gpio_free(gpio_dev->gpio_nr);
kfree(gpio_dev);
return 0;
}
#ifdef CONFIG_PM
static int gpio_ir_recv_suspend(struct device *dev)
{
struct platform_device *pdev = to_platform_device(dev);
struct gpio_rc_dev *gpio_dev = platform_get_drvdata(pdev);
if (device_may_wakeup(dev))
enable_irq_wake(gpio_to_irq(gpio_dev->gpio_nr));
else
disable_irq(gpio_to_irq(gpio_dev->gpio_nr));
return 0;
}
static int gpio_ir_recv_resume(struct device *dev)
{
struct platform_device *pdev = to_platform_device(dev);
struct gpio_rc_dev *gpio_dev = platform_get_drvdata(pdev);
if (device_may_wakeup(dev))
disable_irq_wake(gpio_to_irq(gpio_dev->gpio_nr));
else
enable_irq(gpio_to_irq(gpio_dev->gpio_nr));
return 0;
}
static const struct dev_pm_ops gpio_ir_recv_pm_ops = {
.suspend = gpio_ir_recv_suspend,
.resume = gpio_ir_recv_resume,
};
#endif
static struct platform_driver gpio_ir_recv_driver = {
.probe = gpio_ir_recv_probe,
.remove = gpio_ir_recv_remove,
.driver = {
.name = GPIO_IR_DRIVER_NAME,
.of_match_table = of_match_ptr(gpio_ir_recv_of_match),
#ifdef CONFIG_PM
.pm = &gpio_ir_recv_pm_ops,
#endif
},
};
module_platform_driver(gpio_ir_recv_driver);
MODULE_DESCRIPTION("GPIO IR Receiver driver");
MODULE_LICENSE("GPL v2");

ir-nec-decoder.c

/* ir-nec-decoder.c - handle NEC IR Pulse/Space protocol
*
* Copyright (C) 2010 by Mauro Carvalho Chehab
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation version 2 of the License.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*/
#include <linux/bitrev.h>
#include <linux/module.h>
#include "rc-core-priv.h"
#define NEC_NBITS 32
#define NEC_UNIT 562500 /* ns */
#define NEC_HEADER_PULSE (16 * NEC_UNIT)
#define NECX_HEADER_PULSE (8 * NEC_UNIT) /* Less common NEC variant */
#define NEC_HEADER_SPACE (8 * NEC_UNIT)
#define NEC_REPEAT_SPACE (4 * NEC_UNIT)
#define NEC_BIT_PULSE (1 * NEC_UNIT)
#define NEC_BIT_0_SPACE (1 * NEC_UNIT)
#define NEC_BIT_1_SPACE (3 * NEC_UNIT)
#define NEC_TRAILER_PULSE (1 * NEC_UNIT)
#define NEC_TRAILER_SPACE (10 * NEC_UNIT) /* even longer in reality */
#define NECX_REPEAT_BITS 1
enum nec_state {
STATE_INACTIVE,
STATE_HEADER_SPACE,
STATE_BIT_PULSE,
STATE_BIT_SPACE,
STATE_TRAILER_PULSE,
STATE_TRAILER_SPACE,
};
/**
* ir_nec_decode() - Decode one NEC pulse or space
* @dev: the struct rc_dev descriptor of the device
* @duration: the struct ir_raw_event descriptor of the pulse/space
*
* This function returns -EINVAL if the pulse violates the state machine
*/
static int ir_nec_decode(struct rc_dev *dev, struct ir_raw_event ev)
{
struct nec_dec *data = &dev->raw->nec;
u32 scancode;
u8 address, not_address, command, not_command;
bool send_32bits = false;
if (!(dev->enabled_protocols & RC_BIT_NEC))
return 0;
if (!is_timing_event(ev)) {
if (ev.reset)
data->state = STATE_INACTIVE;
return 0;
}
IR_dprintk(2, "NEC decode started at state %d (%uus %s)\n",
data->state, TO_US(ev.duration), TO_STR(ev.pulse));
switch (data->state) {
case STATE_INACTIVE:
if (!ev.pulse)
break;
if (eq_margin(ev.duration, NEC_HEADER_PULSE, NEC_UNIT * 2)) {
data->is_nec_x = false;
data->necx_repeat = false;
} else if (eq_margin(ev.duration, NECX_HEADER_PULSE, NEC_UNIT / 2))
data->is_nec_x = true;
else
break;
data->count = 0;
data->state = STATE_HEADER_SPACE;
return 0;
case STATE_HEADER_SPACE:
if (ev.pulse)
break;
if (eq_margin(ev.duration, NEC_HEADER_SPACE, NEC_UNIT)) {
data->state = STATE_BIT_PULSE;
return 0;
} else if (eq_margin(ev.duration, NEC_REPEAT_SPACE, NEC_UNIT / 2)) {
if (!dev->keypressed) {
IR_dprintk(1, "Discarding last key repeat: event after key up\n");
} else {
rc_repeat(dev);
IR_dprintk(1, "Repeat last key\n");
data->state = STATE_TRAILER_PULSE;
}
return 0;
}
break;
case STATE_BIT_PULSE:
if (!ev.pulse)
break;
if (!eq_margin(ev.duration, NEC_BIT_PULSE, NEC_UNIT / 2))
break;
data->state = STATE_BIT_SPACE;
return 0;
case STATE_BIT_SPACE:
if (ev.pulse)
break;
if (data->necx_repeat && data->count == NECX_REPEAT_BITS &&
geq_margin(ev.duration,
NEC_TRAILER_SPACE, NEC_UNIT / 2)) {
IR_dprintk(1, "Repeat last key\n");
rc_repeat(dev);
data->state = STATE_INACTIVE;
return 0;
} else if (data->count > NECX_REPEAT_BITS)
data->necx_repeat = false;
data->bits <<= 1;
if (eq_margin(ev.duration, NEC_BIT_1_SPACE, NEC_UNIT / 2)
data->bits |= 1;
else if (!eq_margin(ev.duration, NEC_BIT_0_SPACE, NEC_UNIT / 2))
break;
data->count++;
if (data->count == NEC_NBITS)
data->state = STATE_TRAILER_PULSE;
else
data->state = STATE_BIT_PULSE;
return 0;
case STATE_TRAILER_PULSE:
if (!ev.pulse)
break;
if (!eq_margin(ev.duration, NEC_TRAILER_PULSE, NEC_UNIT / 2))
break;
data->state = STATE_TRAILER_SPACE;
return 0;
case STATE_TRAILER_SPACE:
if (ev.pulse)
break;
if (!geq_margin(ev.duration, NEC_TRAILER_SPACE, NEC_UNIT / 2))
break;
address = bitrev8((data->bits >> 24) & 0xff);
not_address = bitrev8((data->bits >> 16) & 0xff);
command = bitrev8((data->bits >> 8) & 0xff);
not_command = bitrev8((data->bits >> 0) & 0xff);
if ((command ^ not_command) != 0xff) {
IR_dprintk(1, "NEC checksum error: received 0x%08x\n",
data->bits);
send_32bits = true;
}
if (send_32bits) {
/* NEC transport, but modified protocol, used by at
* least Apple and TiVo remotes */
scancode = data->bits;
IR_dprintk(1, "NEC (modified) scancode 0x%08x\n", scancode);
} else if ((address ^ not_address) != 0xff) {
/* Extended NEC */
scancode = address << 16 |
not_address << 8 |
command;
IR_dprintk(1, "NEC (Ext) scancode 0x%06x\n", scancode);
} else {
/* Normal NEC */
scancode = address << 8 | command;
IR_dprintk(1, "NEC scancode 0x%04x\n", scancode);
}
if (data->is_nec_x)
data->necx_repeat = true;
rc_keydown(dev, RC_TYPE_NEC, scancode, 0);
data->state = STATE_INACTIVE;
return 0;
}
IR_dprintk(1, "NEC decode failed at count %d state %d (%uus %s)\n",
data->count, data->state, TO_US(ev.duration), TO_STR(ev.pulse));
data->state = STATE_INACTIVE;
return -EINVAL;
}
static struct ir_raw_handler nec_handler = {
.protocols = RC_BIT_NEC,
.decode = ir_nec_decode,
};
static int __init ir_nec_decode_init(void)
{
ir_raw_handler_register(&nec_handler);
printk(KERN_INFO "IR NEC protocol handler initialized\n");
return 0;
}
static void __exit ir_nec_decode_exit(void)
{
ir_raw_handler_unregister(&nec_handler);
}
module_init(ir_nec_decode_init);
module_exit(ir_nec_decode_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Mauro Carvalho Chehab");
MODULE_AUTHOR("Red Hat Inc. (http://www.redhat.com)");
MODULE_DESCRIPTION("NEC IR protocol decoder");

参考文章中的dts文件：

gpio-ir-receiver {
compatible = "gpio-ir-receiver";
gpios = <&gpio4 19 GPIO_ACTIVE_HIGH>; //连接红外的中断引脚
active_low = <1>; //红外接收器是否将信号取反，有些红外接收器会将接收到的高低电平信号反向输出，比如我使用的hx1838红外接收器
linux,rc-map-name = "rc-hx18380-carmp3"; //红外scancode与实际input_evnent code映射表名称，要在rc_register_device注册，具体见gpio-ir-recv.c
allowed_protos = <0x100>; /*NEC protocol*/ //保留，驱动中并未使用
};

另一个文件里面调用的
ir-nec-decoder.c

这个函数是Linux内核中的红外处理申请函数

这里主要是注册一个解码的结构体
ir-nec-decoder.c

3.中断处理程序解析
gpio-ir-recv.c

ir_raw_event_store_edge（）这个函数用来计算电平的持续时间。
ir_raw_event_handle（）用来处理这个电平表示什么含义。

驱动程序里面，首先是判断当前GPIO电平，如果是低电平，就进入红外解析，如果不是，或者获取失败，就退出程序。
4.红外数据处理程序解析
内核专门开了一个线程来处理数据解析
rc-ir-raw.c

处理函数其实就是处理电平时间长短来决定数字信号
ir-nec-decoder.c

这里是判断头，这个时间和9ms进行比较

9ms 从哪里来的,可以看看这里
ir-nec-decoder.c

拿到头后，这个switch函数就继续往下跑
ir-nec-decoder.c

然后就是判断 1 和 0 的时候了

ir-nec-decoder.c

上面那个就是1，下面那个就是0。
4.然后数据怎么上报呢？
ir-nec-decoder.c

这里是在另一个模块中注册的映射
不同的红外键值对应不同的上报按键键值
rc-trekstor.c

原文链接：https://mp.weixin.qq.com/s/mwjY69oSF8WjnZ2B8a8Xeg

[Linux] Linux红外驱动重点解析

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