Android 9 读写eeprom at24c256

Android 9 读写eeprom at24c256

linux 读取eeprom相对来说比较简单，因为内核中集成了大部分eeprom的驱动，文件目录在kernel/drivers/misc/eeprom/at24.c 。
而且我们不用区分at24cxx的不同容量导致的读写方式不同，只要将at24.c编译到内核，然后dts中注册相应的i2c通道即可。手中的模块a0 a1 a2 都是接地，所以器件地址为0xa0，而dts中注册为七位地址，即0x50.

&i2c1 {
	status = "okay";
	clock-frequency = <300000>;
	pinctrl-names="default";
	pinctrl-0=<&i2c1_h_pins>;
	at24c256@50{
		compatible = "at24,24c256";
		reg = <0x50>;
		status = "okay";
	};
};

按理说升级编译好的kernel后，就应该在对应的i2c节点下找到eeprom的节点，可是找来找去都没有找到这个节点，查看代码发现有这么个东西。

	at24->nvmem_config.name = dev_name(&client->dev);
	at24->nvmem_config.dev = &client->dev;
	at24->nvmem_config.read_only = !writable;
	at24->nvmem_config.root_only = true;
	at24->nvmem_config.owner = THIS_MODULE;
	at24->nvmem_config.compat = true;
	at24->nvmem_config.base_dev = &client->dev;
	at24->nvmem_config.reg_read = at24_read;
	at24->nvmem_config.reg_write = at24_write;
	at24->nvmem_config.priv = at24;
	at24->nvmem_config.stride = 1;
	at24->nvmem_config.word_size = 1;
	at24->nvmem_config.size = chip.byte_len;
	at24->nvmem = nvmem_register(&at24->nvmem_config);
	if (IS_ERR(at24->nvmem)) {
		err = PTR_ERR(at24->nvmem);
		goto err_clients;
	}

原来新的内核中引入了nvmem的架构对eeprom操作。重新配置内核，打开nvmem的编译选项，重新升级后，找到了nvmem的节点。

应用层对eeprom的操作，都是通过这个节点。

写个应用层代码：

#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include "android/log.h"
#include <cutils/properties.h>
#include <stdbool.h>
#include <linux/input.h>

#define FILE_PATH  "/sys/bus/nvmem/devices/1-00500/nvmem"

int main()
{
	int fd;
	int size;
	
	char data[512] = {0};
	char r_data[64] = {0};
	char *w_data = "Hello World!Good Day!\n";
	fd = open(FILE_PATH, O_RDWR);
	if (fd < 0) {
	
		printf("Can't open file %s\r\n", FILE_PATH);
		return -1;
	}

	lseek(fd,0,SEEK_SET);
	write(fd,data,sizeof(data)); //erase eeprom
	lseek(fd,0,SEEK_SET);
	write(fd,w_data,strlen(w_data));
	lseek(fd,0,SEEK_SET);
	size = read(fd,r_data,sizeof(r_data));
	printf("read data==%s\n",r_data);
	close(fd);
	return 0;
}

Android.mk

LOCAL_PATH:= $(call my-dir)
include $(CLEAR_VARS)
LOCAL_SRC_FILES:= max.c
LOCAL_MODULE := max
LOCAL_MODULE_TAGS := optional
LOCAL_SHARED_LIBRARIES += \
	libcutils \
	liblog 
LOCAL_MODULE_PATH :=$(PRODUCT_OUT)/vendor/bin
include $(BUILD_EXECUTABLE)

运行结果如图

本文地址：https://blog.csdn.net/weixin_43932857/article/details/110622051