ARM 上 Linux 中的 WRITE 和 READ 内存映射设备寄存器 [英] WRITE and READ memory mapped device registers in Linux on ARM
问题描述
我正在尝试按照以下步骤在我的 ARM9 (SAM9X25) 上读取和写入寄存器:http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.faqs/ka3750.html
我以以下代码结束:
I am trying to read and write registers on my ARM9 (SAM9X25) following those steps : http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.faqs/ka3750.html
I ended with the following code :
#include "stdio.h"
#define PIO_WPMR_BANK_D 0xFFFFFAE4 // PIO Write Protection Mode Register Bank D
#define PIO_PUER_BANK_D 0xFFFFFA64 // PIO Pull-Up Enable Register Bank D
#define PIO_PUSR_BANK_D 0xFFFFFA68 // PIO Pull-Up Status Register Bank D
#define MASK_LED7 0xFFDFFFFF // LED7 Mask
#define DESABLE_WRITE_PROTECTION_BANK_D 0x50494F00 // Desable write protection Bank D
int main(void) {
printf("test");
unsigned int volatile * const register_PIO_WPMR_BANK_D = (unsigned int *) PIO_WPMR_BANK_D;
unsigned int volatile * const register_PIO_PUSR_BANK_D = (unsigned int *) PIO_PUSR_BANK_D;
unsigned int volatile * const port_D = (unsigned int *) PIO_PUER_BANK_D;
*register_PIO_WPMR_BANK_D = DESABLE_WRITE_PROTECTION_BANK_D;
*port_D = *register_PIO_PUSR_BANK_D & MASK_LED7;
return 0; }
我在 Ubuntu 16.04 中交叉编译了我的代码，就像这样 arm-linux-gnueabi-gcc gpio.c -o gpio
但是我有一个 Segmentation Fault 在我板上的程序执行期间，就在 printf 之后.
我知道地址是正确的...那为什么我会出现这个错误?
这是个好方法吗?
谢谢你的帮助！
I cross compiled my code in Ubuntu 16.04 like so arm-linux-gnueabi-gcc gpio.c -o gpio
But I have a Segmentation Fault just after the printf during the execution of the program on my board.
I know the addresses are right... So why do I have this error?
Is it the good way ?
Thank you for your help !
解决方案:
谢谢@vlk，我可以让它工作！这是一个切换 LED 的小例子:
SOLUTION :
Thank you to @vlk I could make it work ! Here is a little example for toggling a LED :
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <fcntl.h>
#define handle_error(msg)
do { perror(msg); exit(EXIT_FAILURE); } while (0)
#define _PIOD_BANK_D 0xA00
#define _PIO_OFFSET 0xFFFFF000
/* When executing this on the board :
long sz = sysconf(_SC_PAGESIZE);
printf("%ld
",sz);
We have 4096.
*/
#define _MAP_SIZE 0x1000 // 4096
#define _WPMR_OFFSET 0x0E4 // PIO Write Protection Mode Register Bank D
#define _PIO_ENABLE 0x000
#define _PIO_DISABLE 0x004
#define _PIO_STATUS 0x008
#define _OUTPUT_ENABLE 0x010
#define _OUTPUT_DISABLE 0x014
#define _OUTPUT_STATUS 0x018
#define _FILTER_ENABLE 0x020
#define _FILTER_DISABLE 0x024
#define _FILTER_STATUS 0x028
#define _OUTPUT_DATA_SET 0x030
#define _OUTPUT_DATA_CLEAR 0x034
#define _OUTPUT_DATA_STATUS 0x038
#define _PIN_DATA_STATUS 0x03c
#define _MULTI_DRIVER_ENABLE 0x050
#define _MULTI_DRIVER_DISABLE 0x054
#define _MULTI_DRIVER_STATUS 0x058
#define _PULL_UP_DISABLE 0x060
#define _PULL_UP_ENABLE 0x064
#define _PULL_UP_STATUS 0x068
#define _PULL_DOWN_DISABLE 0x090
#define _PULL_DOWN_ENABLE 0x094
#define _PULL_DOWN_STATUS 0x098
#define _DISABLE_WRITE_PROTECTION 0x50494F00 // Desable write protection
#define LED_PIN 21
int main(void) {
volatile void *gpio_addr;
volatile unsigned int *gpio_enable_addr;
volatile unsigned int *gpio_output_mode_addr;
volatile unsigned int *gpio_output_set_addr;
volatile unsigned int *gpio_output_clear_addr;
volatile unsigned int *gpio_data_status_addr;
volatile unsigned int *gpio_write_protection_addr;
int fd = open("/dev/mem", O_RDWR|O_SYNC);
if (fd < 0){
fprintf(stderr, "Unable to open port
");
exit(fd);
}
gpio_addr = mmap(NULL, _MAP_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, _PIO_OFFSET);
if(gpio_addr == MAP_FAILED){
handle_error("mmap");
}
gpio_write_protection_addr = gpio_addr + _PIOD_BANK_D + _WPMR_OFFSET;
gpio_enable_addr = gpio_addr + _PIOD_BANK_D + _PIO_ENABLE;
gpio_output_mode_addr = gpio_addr + _PIOD_BANK_D + _OUTPUT_ENABLE;
gpio_output_set_addr = gpio_addr + _PIOD_BANK_D + _OUTPUT_DATA_SET;
gpio_output_clear_addr = gpio_addr + _PIOD_BANK_D + _OUTPUT_DATA_CLEAR;
gpio_data_status_addr = gpio_addr + _PIOD_BANK_D + _OUTPUT_DATA_STATUS;
*gpio_write_protection_addr = _DISABLE_WRITE_PROTECTION;
*gpio_enable_addr = 1 << LED_PIN;
*gpio_output_mode_addr = 1 << LED_PIN; // Output
// If LED
if((*gpio_data_status_addr & (1<<LED_PIN)) > 0){
*gpio_output_clear_addr = 1 << LED_PIN;
}else{
*gpio_output_set_addr = 1 << LED_PIN;
}
return 0;
}
回答评论中的3).如果您希望它使用所有偏移量，您必须更改 mmap 和分配(即:mmap 示例):
EDIT :
Answer for the 3) in the comments. You have to change the mmap and the assignations like so if you want it to work with all the offsets (i.e : mmap example):
#define _PIO_OFFSET 0xFFFFFA00 // Instead of 0xFFFFF000
#define _MAP_SIZE 0x1000 // 4096
#define _MAP_MASK (_MAP_SIZE - 1)
#define _PA_OFFSET _PIO_OFFSET & ~_MAP_MASK
还有mmap:
gpio_addr = mmap(NULL, _MAP_SIZE + _PIO_OFFSET - _PA_OFFSET, PROT_READ | PROT_WRITE, MAP_SHARED, fd, _PA_OFFSET);
对于分配:
gpio_enable_addr = gpio_addr + _PIO_OFFSET - (_PA_OFFSET) + _PIO_ENABLE;
推荐答案
你不能直接访问寄存器，因为 Linux 使用 MMU，这会为你的应用程序创建不同于物理 MCU 地址空间的虚拟地址空间，并在此之外访问虚拟地址空间导致分段错误.
You can't access registers directly, because Linux use MMU and this create for your application virtual address space which is different than physical MCU address space and access outside this virtual address space cause segmentation fault.
在 Linux 中访问这些寄存器的唯一方法(如果您不想编写内核驱动程序)是将文件/dev/mem 作为文件打开并使用 mmap
Only Way to access these registers in Linux (if you don't want to write kernel drivers) is to open file /dev/mem as file and map it with mmap
例如，我有一个小型 python 库，用于访问 Atmel SAM MCU gpiosam 上的 GPIO 寄存器.您可以激发灵感并将其移植到 C.
For example I have small python library for access GPIO registers on Atmel SAM MCU gpiosam. You can inspire and port it to C.
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