i2c访问外接AT24C256 EEPROM

soloforce

发个i2c访问at24c256 eeprom( at24c256.pdf (362.27 KB, 下载次数: 18)

2013-11-18 19:25 上传

点击文件名下载附件

)的DIY，按例先上图。





用了四个at24c256, 并联在Cubieboard的TWI-1接口上，设备文件是/dev/i2c-1。下面我画的示意图有点小错，把WP脚接VCC了，会导致写保护（无法写入），必须悬空掉。


为了更清楚地了解at24c，给个设备编址说明，网上下载的，不过有错误，我已经修正了。

研究了一下午i2c on linux，终于写出了代码：

1. 
   
2. /*
   
3. * at24c256_i2c.c
   
4. *
   
5. * This script is a demo for AT24C256 EEPROM access via I2C on Cubieboard
   
6. *
   
7. * Author: soloforce, forum.cubietech.com
   
8. * Date: 2013.11.18
   
9. *
   
10. * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
    
11. * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    
12. * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
    
13. * PAWEL W. OLSZTA BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
    
14. * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
    
15. * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
    
16. *
    
17. */
    
18. 
    
19. #include <stdio.h>
    
20. #include <stdlib.h>
    
21. #include <unistd.h>
    
22. #include <fcntl.h>
    
23. #include <sys/ioctl.h>
    
24. #include <linux/i2c-dev.h>
    
25. 
    
26. // Cubieboard IO port PB18 & PB19 are configured to TWI1-SCK & TWI1-SDA (I2C-1)
    
27. #define DEFAULT_AT24C256_DEV  "/dev/i2c-1"
    
28. 
    
29. // ATmega AT24C series EEPROM slave devices are addressed from 0x50~0x57
    
30. // As for AT24C256, should be 0x50~0x53
    
31. #define DEFAULT_AT24C256_ADDRESS 0x50
    
32. 
    
33. // AT24C256 has 512 pages, 64 bytes each
    
34. #define PAGE_BYTES  64  
    
35. 
    
36. typedef unsigned char uint8;
    
37. typedef unsigned short uint16;
    
38. 
    
39. /*
    
40. * Open the i2c bus device
    
41. */
    
42. int init_at24c256_i2c(const char* device)
    
43. {
    
44.     int fd=open(device, O_RDWR);
    
45.     if(fd<0){
    
46.         perror("Failed to open I2C device!");
    
47.         return -1;
    
48.     }
    
49. 
    
50.     ioctl(fd, I2C_TIMEOUT, 3);        // i2c timeout, 1 for 10ms ; if too small, i2c may lose response
    
51.     ioctl(fd, I2C_RETRIES, 3);        // i2c retry limit
    
52.    
    
53.     return fd;
    
54. }
    
55. 
    
56. /*
    
57. * Page write (or partially page write), data_len should less than PAGE_BYTES
    
58. *
    
59. */
    
60. int at24c256_write(int fd, int device_addr, uint16 offset, const char* data, int data_len)
    
61. {
    
62.     struct i2c_rdwr_ioctl_data at24c256;        // structure pass to i2c driver
    
63.     struct i2c_msg i2cmsg;
    
64. 
    
65.     if(data_len>PAGE_BYTES){
    
66.         printf("*** Warning: Page write mode should not exceed %d bytes, otherwise the current page will be rolled over!\n",PAGE_BYTES);
    
67.     }
    
68. 
    
69.     at24c256.nmsgs = 1;        // message count in the structure
    
70.     at24c256.msgs = &i2cmsg;
    
71.     at24c256.msgs[0].len = 2 + data_len;        // the offset address word is 2 bytes long, plus the buf_len
    
72.     at24c256.msgs[0].addr = device_addr;        // i2c slave device address
    
73.     at24c256.msgs[0].flags = 0;        // 0 for write; 1 for read
    
74.     at24c256.msgs[0].buf = (uint8 *)malloc( at24c256.msgs[0].len );
    
75.     if(!at24c256.msgs[0].buf){
    
76.         printf("at24c256_write(): Failed to allocate memory for i2c message buffer!\n");
    
77.         return -1;
    
78.     }
    
79.    
    
80.     at24c256.msgs[0].buf[0] = (uint8)(offset >> 8);        // MSB first
    
81.     at24c256.msgs[0].buf[1] = (uint8)(offset);        // LSB
    
82.     strncpy( at24c256.msgs[0].buf+2, data, data_len); // copy user's data to the structure buffer
    
83. 
    
84.     if(ioctl(fd, I2C_RDWR, (unsigned long)&at24c256)<0 ){        // write ioctl data to the i2c bus
    
85.         printf("at24c256_write(): Failed to write data to i2c device!\n");
    
86.         free(at24c256.msgs[0].buf);
    
87.         return -1;
    
88.     }
    
89.    
    
90.     free(at24c256.msgs[0].buf);
    
91.     return 0;
    
92. }
    
93. 
    
94. /*
    
95. * Sequential read from AT24C256, data_len should less than PAGE_BYTES
    
96. */
    
97. int at24c256_read(int fd, int device_addr, uint16 offset, char* data, int data_len)
    
98. {
    
99.     struct i2c_rdwr_ioctl_data at24c256;        // structure pass to i2c driver
    
100.     struct i2c_msg i2cmsg[2]; // message count in the structure
     
101.     char dummy_write_buf[2];
     
102.    
     
103.     if(data_len>PAGE_BYTES){
     
104.         printf("*** Warning: Sequential read should not exceed %d bytes, otherwise the read data will be rolled over!\n",PAGE_BYTES);
     
105.     }
     
106. 
     
107.     // A dummy write operation should be done according to the AT24C256 i2c protocol
     
108.     at24c256.nmsgs = 2;        // message count in the structure
     
109.     at24c256.msgs = i2cmsg;
     
110.     at24c256.msgs[0].len = 2; // the offset address word is 2 bytes long
     
111.     at24c256.msgs[0].addr = device_addr;
     
112.     at24c256.msgs[0].flags = 0;        // 0 for write;
     
113.     at24c256.msgs[0].buf = dummy_write_buf;
     
114.     at24c256.msgs[0].buf[0] = (unsigned char)(offset >> 8);        // write address
     
115.     at24c256.msgs[0].buf[1] = (unsigned char)(offset);        // write address
     
116. 
     
117.     // read operation
     
118.     at24c256.msgs[1].len = data_len;
     
119.     at24c256.msgs[1].addr = device_addr;
     
120.     at24c256.msgs[1].flags = 1;        // 1 for read; 0 for write
     
121.     at24c256.msgs[1].buf = data;
     
122. 
     
123.     if (ioctl(fd, I2C_RDWR, (unsigned long)&at24c256) < 0) {
     
124.         printf("at24c256_read(): Failed to read data from EEPROM via i2c!\n");
     
125.         return -1;
     
126.     }
     
127. 
     
128.     return 0;
     
129. }
     
130. 
     
131. /*
     
132. * Show help message
     
133. */
     
134. void show_usage(char* argv[])
     
135. {
     
136.     printf("%s <-d device> <-a address> [-o offset] [-r length] [-w data] [-h]\n",argv[0]);
     
137.     printf("\t-d device: i2c device file, like /dev/i2c-1 by default\n");
     
138.     printf("\t-a address: i2c slave device base address, like 0x50 by default\n");
     
139.     printf("\t-o offset: offset from base address, like 0x00, 0x10 ...\n");
     
140.     printf("\t-r length: read length bytes from at24c256 eeprom\n");
     
141.     printf("\t-w data: write to at24c256 eeprom\n");
     
142.     printf("\t-h: show help message\n\n");
     
143. }
     
144. 
     
145. int main(int argc, char* argv[])
     
146. {
     
147.     char* device=DEFAULT_AT24C256_DEV;
     
148.     int slave_address=DEFAULT_AT24C256_ADDRESS;
     
149.     int offset=0x00; // default offset is 0
     
150.     int length=32; // read 32 bytes by default
     
151.     char* data=NULL;
     
152.     int rw_mode=1; // 0 for write, 1 for read;
     
153. 
     
154.     if(argc==1){
     
155.         show_usage(argv);
     
156.         return 0;
     
157.     }
     
158. 
     
159.     int i;
     
160.     while ((i = getopt(argc, argv, "d:a:o:r:w:n:h")) >= 0){
     
161.         switch(i){
     
162.         case 'd':
     
163.             device=optarg;
     
164.             break;
     
165.         case 'a':
     
166.             if (sscanf(optarg, "0x%x", &slave_address) != 1) {
     
167.             fprintf(stderr, "Cannot parse '%s' as i2c slave device address, example: '0x50'\n", optarg);
     
168.                 return -1;
     
169.             }
     
170.             break;
     
171.         case 'o':
     
172.             if (sscanf(optarg, "%d", &offset) != 1) {
     
173.             fprintf(stderr, "Cannot parse '%s' as address offset, example: '32'\n", optarg);
     
174.                 return -1;
     
175.             }
     
176.             break;
     
177.         case 'r':
     
178.             rw_mode=1;
     
179.             if (sscanf(optarg, "%d", &length) != 1) {
     
180.                 fprintf(stderr, "Cannot parse '%s' as length, example: '17'\n", optarg);
     
181.                 return -1;
     
182.             }
     
183.             break;
     
184.         case 'w':
     
185.             rw_mode=0;
     
186.             data=optarg;
     
187.             length=strlen(data);
     
188.             break;
     
189.         case 'h':
     
190.             show_usage(argv);
     
191.             return 0;
     
192.             break;
     
193.         }
     
194.     }
     
195.    
     
196.     int fd=init_at24c256_i2c(device);
     
197.     if(fd<0) return -1;
     
198. 
     
199.     printf("i2c device file:%s\nslave_address:0x%X\nR/W offset:0x%X\n",device, slave_address, offset);
     
200. 
     
201.     if(rw_mode==0){
     
202.         // test at24c256 write
     
203.         at24c256_write(fd, slave_address, offset, data, length);
     
204.         printf("try to write: %s (%d bytes)!\n",data,length);
     
205.         usleep(10000); // some delay is necessary for the write operation done
     
206.     }else if(rw_mode==1){
     
207.         // test at24c256 read
     
208.         char *buf=(char*)malloc(length+1);
     
209.         memset(buf,0,length+1);
     
210.         at24c256_read(fd, slave_address, offset, buf, length);
     
211.         usleep(10000); // necessary for the read operation done
     
212.         
     
213.         printf("read from at24c256 eeprom: %s (%d bytes)\n", buf, strlen(buf));
     
214.         free(buf);
     
215.     }
     
216.    
     
217.     close(fd);
     
218. }
     
219. 
     

复制代码

rgwan

当年用8051驱动 24C02那个心酸啊，代码一长串的。
注意一下24系列的ROM的死区时间是8ms左右。如果两次写入间隔时间太短会没有响应。

sunbeyond

怎么报错了。at24.c:48:12: error: invalid use of undefined type ‘struct i2c_msg’
这个结构体没声明啊。差那个头文件了吗？

lknlfy

不错，基于应用层的驱动

lknlfy

内核有专门针对at eeprom的驱动