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嵌入式系統

UIO-Linux user space I/O driver

作者: Joey 日期: 2008-12-15 14:50

字體大小: 小中大

有一陣子沒寫部落格了,最近都在研究RTP的CODEC,真佩服那些電機電子的人,可以想到那麼多的好點子壓縮語音和資料,而且壓縮率還非常驚人,以G729A為例,160 byte的語音資料經過壓縮居然只剩10byte…天阿,寫程式也沒這麼精簡

回到主題,UIO這個東西是雖然是今年四月份的時候merge到kernel trunk,但其實在linux界很早就有相關的應用,因為它的技術很簡單,就是直接把kernel memory一對一映射到user space memory,藉由這樣mapping的方式,讓user program直接在user space存取hardware I/O

而UIO在kernel提供了一個簡單的架構,programmer只要設定好IO address和size,就可以使用UIO的功能,UIO會自動幫我們處理VMA相關的轉換動作,而UIO drvier的撰寫順序如下
1.宣告struct uio_info,並填入hardware資料
uio_info.name:drvier的名稱
uio_info.version:driver版本
uio_info.irq:中斷編號
uio_info.irq_flags:request_irq時需傳入的參數
uio_info.handler:中斷handler
uio_info.mem[]:hardware IO映射位址,可以有很多組
2.user space的程式很簡單,就是用open和mmap去存取hardware I/O

QT2410 LED UIO的範例我簡述如下,因為我driver註冊為platform driver,所以有改到arch/arm/mach-s3c2410/mach-smdk2410.c,請參照如下修改

static struct resource s3c_led_resources[] = {

[0] = {

.start = 0x56000000,

.end = 0x56000000 + 24,

.flags = IORESOURCE_MEM,

[1] = {

.start = IRQ_EINT23,

.end = IRQ_EINT23,

.flags = IORESOURCE_IRQ,

};

static struct platform_device s3c_led = {

.name = "JoeyLED",

.num_resources = ARRAY_SIZE(s3c_led_resources),

.resource = s3c_led_resources,

};

static struct platform_device *smdk2410_devices[] __initdata = {

&s3c_device_usb,

&s3c_device_lcd,

&s3c_device_wdt,

&s3c_device_i2c,

&s3c_device_iis,

&s3c_cs89x0,

&s3c_led,

};

新增led.c這個UIO driver,範例程式如下,重點在led_probe這個函式,可以看看該如何填寫uio_info這個structure的資料

#include <linux/module.h>

#include <linux/kernel.h>

#include <linux/init.h>

#include <linux/proc_fs.h>

#include <asm/uaccess.h>

#include <linux/ioport.h>

#include <asm/io.h>

#include <linux/uio_driver.h>

#include <linux/platform_device.h>

#define GPIOBAdr 0x56000014

#define DRV_NAME "JoeyLED"

#define DRV_VERSION "0.0.1"

static irqreturn_t led_handler(int irq, struct uio_info *dev_info)

{

printk("interrupt happened\n");

return IRQ_HANDLED;

}

static int __init led_probe(struct platform_device *dev)

{

struct resource *regs;

struct uio_info *info;

printk("probing led\n");

info = kzalloc(sizeof(struct uio_info), GFP_KERNEL);

if (!info)

return -ENOMEM;

regs = platform_get_resource(dev, IORESOURCE_MEM, 0);

if (!regs)

{

dev_err(&dev->dev, "No memory resource specified\n");

return -ENODEV;

}else

{

printk("GPIOB reg->start %x reg->end %x \n",regs->start,regs->end );

}

info->mem[0].addr = regs->start;

info->mem[0].size=regs->end - regs->start;

info->mem[0].internal_addr=ioremap(regs->start, info->mem[0].size);;

if (!info->mem[0].addr)

{

dev_err(&dev->dev, "Invalid memory resource\n");

return -ENODEV;

}

info->mem[0].memtype = UIO_MEM_PHYS;

info->version = "0.0.1";

info->name="JoeyLED";

info->irq=platform_get_irq(dev, 0);

info->irq_flags = IRQF_SHARED;

info->handler = led_handler;

if (uio_register_device(&dev->dev, info))

{

iounmap(info->mem[0].internal_addr);

printk("uio_register failed\n");

return -ENODEV;

}

platform_set_drvdata(dev, info);

printk("probing led success\n");

return 0;

}

static int __exit led_remove(struct platform_device *dev)

{

struct uio_info *info = platform_get_drvdata(dev);

uio_unregister_device(info);

platform_set_drvdata(dev, NULL);

iounmap(info->mem[0].internal_addr);

kfree(info);

return 0;

}

static struct platform_driver led_driver = {

.probe = led_probe,

.remove = __devexit_p(led_remove),

.driver = {

.name = DRV_NAME,

.owner = THIS_MODULE,

};

static int __init led_init(void)

{

printk("QT2410 LED driver demo\n");

return platform_driver_register(&led_driver);

}

static void __exit led_exit(void)

{

platform_driver_unregister(&led_driver);

}

module_init(led_init);

module_exit(led_exit);

MODULE_DESCRIPTION("led module");

MODULE_AUTHOR("Joey Cheng<jemicheng@gmail.com>");

MODULE_LICENSE("GPL");

MODULE_ALIAS("QT2410:LED module");

Userspace程式的範例如下

#include <stdio.h>

#include <stdlib.h>

#include<sys/mman.h>

#include<fcntl.h>

#include <asm/page.h>

int main(void)

{

int mem_fd,i=0;

unsigned *led;

mem_fd=open("/dev/uio0",O_RDWR|O_SYNC);

if (mem_fd <0)

{

printf("open device error\n");

return;

}

led=mmap(NULL,24, PROT_READ | PROT_WRITE, MAP_SHARED,mem_fd, 0);

if (led == MAP_FAILED)

{

perror("mmap");

close(mem_fd);

exit(-1);

}

//led+=4;

led+=5;

while(i<3)

{

(*(volatile unsigned *)led)|=0x00000002;

printf("led mem %p content %d\n",led,*(unsigned *)led);

sleep(3);

(*(volatile unsigned *)led)&=~(0x00000002);

printf("led mem %p content %d\n",led,*(unsigned *)led);

i++;

sleep(3);

}

close(mem_fd);

}

記得要在kernel選單中選擇Userspace I/O drivers

重編kernel並試著跑跑看上面的範例來點亮板子上的led,修改過的檔案我簡列如下,記得在執行範例前先確定/dev/uio0是否有建立,請先cat /sys/class/uio/uio0/dev/的資訊,確定device node的major和minor(/sys這個資料夾是virtual sysfs mount出來的,請下指令mount -t sysfs sysfs /sys)

1.arch/arm/mach-s3c2410/mach-smdk2410.c
2.drivers/uio/led_kernel.c
3.drivers/uio/Makefile
4.drivers/uio/Kconfig
5.led.c(in user space)

UIO相關的參考資料請點這裡,這邊有個很棒的軟體叫lsuio,可以列出所有UIO的module和其映射的memory address,執行範例如下圖