IIC读写EEPROM的接口如何高效一些

发布于 2021-01-18 15:40:46 浏览：1793 订阅该版

参考别人的操作24C02的例子,是这样的:
```c
rt_err_t eeprom_iic_write(rt_uint8_t write_addr, rt_uint8_t data, rt_uint32_t number)
{
   rt_uint8_t buf[2];
 
    buf[0] = write_addr; //地址是1字节的
    buf[1] = data;
    rt_size_t result;
  
    result = rt_i2c_master_send(eep_i2c_bus, EEP_ADDR, RT_I2C_WR, buf, 2);
    rt_thread_mdelay(10);  //必须延时
    if (result == 2)
    {
        rt_kprintf("EEP write ok \r\n");
        return RT_EOK;       
    }
    else
    {
        rt_kprintf("EEP write failed ,ERR is: %d \r\n",result);
        return -RT_ERROR;       
    }
}
```
我用的EEPROM是FM24C256,写方式是这样的:
```c
rt_err_t eeprom_write(rt_uint16_t addr, void *buf, rt_uint32_t len)
{
    rt_uint8_t *wrbuf = rt_malloc(len+2);

if(wrbuf != RT_NULL) {
        wrbuf[0] = (addr>>8) & 0xFF;
        wrbuf[1] = addr & 0xFF; //地址是2字节的
        rt_memcpy(wrbuf+2, buf, len);
        if (rt_i2c_master_send(i2c_bus_eeprom, EEPROM_ADDR, RT_I2C_WR, wrbuf, len+2) != (len+2)) {
            rt_kprintf("WR1.EEPROM write failed, addr:%02X%02X\n", wrbuf[0], wrbuf[1]);
            return -RT_ERROR;
        }

rt_free(wrbuf);
    }

return RT_EOK;
}
```
首先,这不是BUG,只是用起来很难受,是我用的姿势不对吗?
```c
struct rt_i2c_msg
{
    rt_uint16_t addr;
    rt_uint16_t flags;
    rt_uint16_t len;
    rt_uint8_t  *buf;
};
```
addr是器件地址,读写的地址放在buf的前面,其后跟着真正的数据;
就第一个例子,一个字节的写入地址,一个字节的写入数据,似乎也没问题,但是谁会每次只读写一个字节呢,这没有现实意义,如果读写多个字节,就只能使用我后面的方式,用户的数据都要拷贝一遍.

##问题:
我用的是铁电,不存在读写延时,但是EEPROM的读写效率被malloc,memcpy拉低了很多.
我试过使用rt_i2c_master_send()先写地址,在写数据,是不行的,这个接口每次调用都会结束一次IIC,导致单独写数据时第一个字节丢失(被作为写入地址了?!)
有没有办法直接使用传入用户的缓冲地址就行.

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RiceChen 认证专家 2021-01-18

内核/软件架构/开源

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这个才是EEPROM的正确操作姿势:
```c
#define EE_PAGESIZE 64
rt_err_t eeprom_write(rt_uint16_t addr, void *buf, rt_uint32_t len)
{
    rt_size_t size;
    rt_uint8_t addr_buf[2];
    rt_uint32_t wrlen;

do {
        wrlen = EE_PAGESIZE - addr % EE_PAGESIZE;
        if (wrlen > len) wrlen = len;
        rt_kprintf("addr=%d, wrlen=%d\n", addr, wrlen); //DEBUG

addr_buf[0] = (addr>>8)&0xFF;
        addr_buf[1] = addr & 0xFF;

size = rt_i2c_master_send(i2c_bus_eeprom, EEPROM_ADDR, RT_I2C_WR|RT_I2C_NO_END, addr_buf, 2); /* fixed: no stop iic */
        if (size != 2) {
            rt_kprintf("RD1.EEPROM write failed, size is:%d\n", size);
            return -RT_ERROR;
        }
#if 0
        //DEBUG
        for(int i=0; i<wrlen; i++) {
            rt_kprintf("%c ", *(char*)(buf+i));
        }
        rt_kprintf("\n");
#endif
        size = rt_i2c_master_send(i2c_bus_eeprom, EEPROM_ADDR, RT_I2C_WR|RT_I2C_NO_START, buf, wrlen); /* fixed: no restart iic */
        if (size != wrlen) {
            rt_kprintf("WR1.EEPROM write failed, addr:%02X%02X, size=%d\n", addr_buf[0], addr_buf[1], size);
            return -RT_ERROR;
        }
        buf  += wrlen; //change to next page data align to EE_PAGESIZE bytes.
        addr += wrlen; //change to next page address.
        len  -= wrlen;
        rt_thread_mdelay(5);//根据器件手册设置延时
    } while (len);

return RT_EOK;
}
#endif

rt_err_t eeprom_read(rt_uint16_t addr, void *buf, rt_uint32_t len)
{
    rt_size_t size;
    rt_uint8_t addr_buf[2];

addr_buf[0] = (addr>>8)&0xFF;
    addr_buf[1] = addr & 0xFF;

size = rt_i2c_master_send(i2c_bus_eeprom, EEPROM_ADDR, RT_I2C_WR, addr_buf, 2);
    if (size != 2) {
        rt_kprintf("RD1.EEPROM write failed, size is:%d\n", size);
        return -RT_ERROR;
    }
    size = rt_i2c_master_recv(i2c_bus_eeprom, EEPROM_ADDR, RT_I2C_RD, buf, len);
    if (size != len) {
        rt_kprintf("RD2.EEPROM write failed, size is:%d\n", size);
        return -RT_ERROR;
    }

return RT_EOK;
}
```
测试代码:
```c
#ifdef RT_USING_FINSH
int ee_test(void)
{
    rt_uint16_t addr = 6410; //100 pages offset 10 bytes
    rt_uint32_t length = 208;
    rt_uint8_t wrbuf[208]={
    'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z',
    'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','X','X','Y','Z',
    '0','1','2','3','4','5','6','7','8','9','~','!','@','#','$','%','^','&','*','(',')','-','=','_','+','`',
    '[',']','{','}','\\','|',';',':','\'','"',',','.','<','>','/','?','0','1','2','3','4','5','6','7','8','9',
    'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z',
    'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','X','X','Y','Z',
    '0','1','2','3','4','5','6','7','8','9','~','!','@','#','$','%','^','&','*','(',')','-','=','_','+','`',
    '[',']','{','}','\\','|',';',':','\'','"',',','.','<','>','/','?','0','1','2','3','4','5','6','7','8','9',
    };
    rt_uint8_t rdbuf[300] = {0};

rt_kprintf("eeprom write:\n");

eeprom_write(addr, wrbuf, length);
    rt_thread_mdelay(5);

////////////////////////////////////
    eeprom_read(addr, rdbuf, length);

rt_kprintf("eeprom read at %d:\n", addr);
    for(int i=0; i<length; i++) {
        rt_kprintf("%c ", rdbuf[i]);
    }
    rt_kprintf("\n");

return 0;
}
MSH_CMD_EXPORT(ee_test, test eeprom read and write.);
```
//修改的地方:
```c
#define RT_I2C_WR                0x0000
#define RT_I2C_RD               (1u << 0)
#define RT_I2C_ADDR_10BIT       (1u << 2)  /* this is a ten bit chip address */
#define RT_I2C_NO_START         (1u << 4)
#define RT_I2C_IGNORE_NACK      (1u << 5)
#define RT_I2C_NO_READ_ACK      (1u << 6)  /* when I2C reading, we do not ACK */
#define RT_I2C_NO_END           (1U << 7)  /* 增加的标志 */
```
RT_I2C_NO_END标志有效时不关闭iic.
**发现2020年9月23日已经更新了这个问题,是我的代码太旧了,没有加入这个标志,汗**
测试结果:
```
msh >ee_test
eeprom write:
addr=6410, wrlen=54
a b c d e f g h i j k l m n o p q r s t u v w x y z A B C D E F G H I J K L M N O P Q R S T U V X X Y Z 0 1
addr=6464, wrlen=64
2 3 4 5 6 7 8 9 ~ ! @ # $ % ^ & * ( ) - = _ + ` [ ] { } \ | ; : ' " , . < > / ? 0 1 2 3 4 5 6 7 8 9 a b c d e f g h i j k l m n
addr=6528, wrlen=64
o p q r s t u v w x y z A B C D E F G H I J K L M N O P Q R S T U V X X Y Z 0 1 2 3 4 5 6 7 8 9 ~ ! @ # $ % ^ & * ( ) - = _ + `
addr=6592, wrlen=26
[ ] { } \ | ; : ' " , . < > / ? 0 1 2 3 4 5 6 7 8 9
eeprom read at 6410:
a b c d e f g h i j k l m n o p q r s t u v w x y z A B C D E F G H I J K L M N O P Q R S T U V X X Y Z 0 1 2 3 4 5 6 7 8 9 ~ ! @ # $ % ^ & * ( ) - = _ + ` [ ] { } \ | ; : ' " , . < > / ? 0 1 2 3 4 5 6 7 8 9 a b c d e f g h i j k l m n o p q r s t u v w x y z A B C D E F G H I J K L M N O P Q R S T U V X X Y Z 0 1 2 3 4 5 6 7 8 9 ~ ! @ # $ % ^ & * ( ) - = _ + ` [ ] { } \ | ; : ' " , . < > / ? 0 1 2 3 4 5 6 7 8 9
msh />
```