基于TQ2440的SPI驱动学习（OLED）

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摘要

这篇博客的目的是简要分析两种spi驱动的实现，一种是利用Samsung的S3C2440自带的硬件SPI控制器，另一种是利用Linux内核已经写好的用GPIO模拟SPI时序，实现一个软件SPI控制器。操作的外设是韦东山的SPI视频教程中提供的OLED模块，同时分享一下在使用逻辑分析仪Saleae16调试SPI时遇到的问题。

相关的内核代码已经上传：[e-mail]:pengdonglin137/linux-3-14-y.git

可以看看代码提交记录。

正文

SPI驱动实现之硬件控制器

一、驱动框架

 

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二、代码

SPI硬件控制器

这里采用的是platform架构，分为device和driver两个部分。

1、platform_device

文件：arch/arm/plat-samsung/devs.c

1: static struct resource s3c_spi0_resource[] = {

2:     [0] = DEFINE_RES_MEM(S3C24XX_PA_SPI, SZ_32),

3:     [1] = DEFINE_RES_IRQ(IRQ_SPI0),

4: };

5:

6: static void s3c24xx_spi_set_cs(struct s3c2410_spi_info *spi, int cs, int pol)

7: {

8:     gpio_set_value(cs, pol);

9: }

10:

11: static struct s3c2410_spi_info s3c_spi_info[] = {

12:     {

13:         .num_cs  = S3C_GPIO_END,

14:         .bus_num = 0,

15:         .set_cs = s3c24xx_spi_set_cs,

16:     }

17: };

18:

19: struct platform_device s3c_device_spi0 = {

20:     .name        = "s3c2410-spi",

21:     .id        = 0,

22:     .num_resources    = ARRAY_SIZE(s3c_spi0_resource),

23:     .resource    = s3c_spi0_resource,

24:     .dev        = {

25:         .dma_mask        = &samsung_device_dma_mask,

26:         .coherent_dma_mask    = DMA_BIT_MASK(32),

27:         .platform_data        = (void *)s3c_spi_info,

28:     }

29: };

第15行是片选函数，它的第二个参数cs来自spi从设备的板级信息，表示这个从设备的片选引脚；

第14行表示spi控制器的编号是0，将来在spi从设备的板级信息中有体现，意思是将来这个spi从设备挂载在编号为0的spi总线下面；

第27行，在linux原生的代码中没有实现platform_data，在调用probe函数的时候会报错；

2、platform_driver

文件：drivers/spi/spi-s3c24xx.c

1: MODULE_ALIAS("platform:s3c2410-spi");

2: static struct platform_driver s3c24xx_spi_driver = {

3:     .probe        = s3c24xx_spi_probe,

4:     .remove        = s3c24xx_spi_remove,

5:     .driver        = {

6:         .name    = "s3c2410-spi",

7:         .owner    = THIS_MODULE,

8:         .pm    = S3C24XX_SPI_PMOPS,

9:     },

10: };

11: module_platform_driver(s3c24xx_spi_driver);

12:

 

OLED 板级信息

这里调用了spi子系统提供的函数接口。

1、板级信息

文件：arch/arm/mach-s3c24xx/mach-tq2440.c

1: /* SPI OLED */

2: static struct spi_board_info tq2440_spi_board_info[] __initdata = {

3:     {

4:         .modalias    = "oled",

5:         .max_speed_hz    = 10000000,

6:         .bus_num    = 0,

7:         .mode        = SPI_MODE_0,

8:         .chip_select    = S3C2410_GPG(1),

9:         .platform_data    = (const void *)S3C2410_GPF(3),

10:     },

11: };

12:

13: static struct platform_device *tq2440_devices[] __initdata = {

14:     ......

15:     &s3c_device_spi0,

16: };

17:

18: static void __init tq2440_machine_init(void)

19: {

20: ......

21:     spi_register_board_info(tq2440_spi_board_info, ARRAY_SIZE(tq2440_spi_board_info));

22: ......

23: }

24:

25: MACHINE_START(TQ2440, "TQ2440")

26: ......

27:     .init_machine    = tq2440_machine_init,

28: ......

29: MACHINE_END

第4行，将来会跟驱动中的name进行匹配；

第5行，表示通信速率，这里设置的是10MHz；

第6行，表示使用的spi总线的编号是0；

第7行，表示使用的spi模式是0，这里要根据oled的芯片手册（SSD1306-Revision 1.1 (Charge Pump).pdf）

第8行，oled使用的片选引脚；

第9行，用于区分命令和数据模式的GPIO资源，这个会在驱动中解析；

第21行，注册spi从设备板级信息；

2、oled驱动

文件：drivers/spi/oled/spi_oled_drv.c

1: #include <linux/init.h>

2: #include <linux/fs.h>

3: #include <linux/slab.h>

4: #include <linux/module.h>

5: #include <linux/kernel.h>

6: #include <linux/device.h>

7: #include <sound/core.h>

8: #include <linux/spi/spi.h>

9: #include <asm/uaccess.h>

10:

11: #include <mach/hardware.h>

12: #include <mach/regs-gpio.h>

13:

14: #include <linux/gpio.h>

15: #include <plat/gpio-cfg.h>

16:

17: /* 构造注册 spi_driver */

18:

19: static int major;

20: static struct class *class;

21:

22: static int spi_oled_dc_pin;

23: static struct spi_device *spi_oled_dev;

24: static unsigned char *ker_buf;

25:

26: static void OLED_Set_DC(char val)

27: {

28:     gpio_set_value(spi_oled_dc_pin, val);

29: }

30:

31: static void OLEDWriteCmd(unsigned char cmd)

32: {

33:     OLED_Set_DC(0); /* command */

34:     spi_write(spi_oled_dev, &cmd, 1);

35:     OLED_Set_DC(1); /*  */

36: }

37:

38: static void OLEDWriteDat(unsigned char dat)

39: {

40:     OLED_Set_DC(1); /* data */

41:     spi_write(spi_oled_dev, &dat, 1);

42:     OLED_Set_DC(1); /*  */

43: }

44:

45: static void OLEDSetPageAddrMode(void)

46: {

47:     OLEDWriteCmd(0x20);

48:     OLEDWriteCmd(0x02);

49: }

50:

51: static void OLEDSetPos(int page, int col)

52: {

53:     OLEDWriteCmd(0xB0 + page); /* page address */

54:

55:     OLEDWriteCmd(col & 0xf);   /* Lower Column Start Address */

56:     OLEDWriteCmd(0x10 + (col >> 4));   /* Lower Higher Start Address */

57: }

58:

59:

60: static void OLEDClear(void)

61: {

62:     int page, i;

63:     for (page = 0; page < 8; page ++)

64:     {

65:         OLEDSetPos(page, 0);

66:         for (i = 0; i < 128; i++)

67:             OLEDWriteDat(0);

68:     }

69: }

70:

71: void OLEDClearPage(int page)

72: {

73:     int i;

74:     OLEDSetPos(page, 0);

75:     for (i = 0; i < 128; i++)

76:         OLEDWriteDat(0);

77: }

78:

79: void OLEDInit(void)

80: {

81:     /* 向OLED发命令以初始化 */

82:     OLEDWriteCmd(0xAE); /*display off*/

83:     OLEDWriteCmd(0x00); /*set lower column address*/

84:     OLEDWriteCmd(0x10); /*set higher column address*/

85:     OLEDWriteCmd(0x40); /*set display start line*/

86:     OLEDWriteCmd(0xB0); /*set page address*/

87:     OLEDWriteCmd(0x81); /*contract control*/

88:     OLEDWriteCmd(0x66); /*128*/

89:     OLEDWriteCmd(0xA1); /*set segment remap*/

90:     OLEDWriteCmd(0xA6); /*normal / reverse*/

91:     OLEDWriteCmd(0xA8); /*multiplex ratio*/

92:     OLEDWriteCmd(0x3F); /*duty = 1/64*/

93:     OLEDWriteCmd(0xC8); /*Com scan direction*/

94:     OLEDWriteCmd(0xD3); /*set display offset*/

95:     OLEDWriteCmd(0x00);

96:     OLEDWriteCmd(0xD5); /*set osc division*/

97:     OLEDWriteCmd(0x80);

98:     OLEDWriteCmd(0xD9); /*set pre-charge period*/

99:     OLEDWriteCmd(0x1f);

100:     OLEDWriteCmd(0xDA); /*set COM pins*/

101:     OLEDWriteCmd(0x12);

102:     OLEDWriteCmd(0xdb); /*set vcomh*/

103:     OLEDWriteCmd(0x30);

104:     OLEDWriteCmd(0x8d); /*set charge pump enable*/

105:     OLEDWriteCmd(0x14);

106:

107:     OLEDSetPageAddrMode();

108:

109:     OLEDClear();

110:

111:     OLEDWriteCmd(0xAF); /*display ON*/

112: }

113:

114:

115: #define OLED_CMD_INIT       0x100001

116: #define OLED_CMD_CLEAR_ALL  0x100002

117: #define OLED_CMD_CLEAR_PAGE 0x100003

118: #define OLED_CMD_SET_POS    0x100004

119:

120: static long oled_ioctl(struct file *file, unsigned int cmd, unsigned long arg)

121: {

122:     int page;

123:     int col;

124:

125:     switch (cmd)

126:     {

127:     case OLED_CMD_INIT:

128:         {

129:             OLEDInit();

130:             break;

131:         }

132:     case OLED_CMD_CLEAR_ALL:

133:         {

134:             OLEDClear();

135:             break;

136:         }

137:     case OLED_CMD_CLEAR_PAGE:

138:         {

139:             page = arg;

140:             OLEDClearPage(page);

141:             break;

142:         }

143:     case OLED_CMD_SET_POS:

144:         {

145:             page = arg & 0xff;

146:             col  = (arg >> 8) & 0xff;

147:             OLEDSetPos(page, col);

148:             break;

149:         }

150:     }

151:     return 0;

152: }

153:

154: static ssize_t oled_write(struct file *file,

155:     const char __user *buf,

156:     size_t count, loff_t *ppos)

157: {

158:     int ret;

159:

160:     if (count > 4096)

161:         return -EINVAL;

162:     ret = copy_from_user(ker_buf, buf, count);

163:     OLED_Set_DC(1); /* data */

164:     spi_write(spi_oled_dev, ker_buf, count);

165:     return 0;

166: }

167:

168:

169: static struct file_operations oled_ops = {

170:     .owner            = THIS_MODULE,

171:     .unlocked_ioctl   = oled_ioctl,

172:     .write            = oled_write,

173: };

174:

175: static int spi_oled_probe(struct spi_device *spi)

176: {

177:     int ret;

178:

179:     spi_oled_dev = spi;

180:     spi_oled_dc_pin = (int)dev_get_platdata(&spi->dev);

181:

182:     ret = devm_gpio_request(&spi->dev, spi_oled_dc_pin, "OLED_DC");

183:     if (ret < 0)

184:         return ret;

185:     gpio_direction_output(spi_oled_dc_pin, 0);

186:

187: #ifndef CONFIG_TQ2440_USE_SPI_GPIO

188:     ret = devm_gpio_request(&spi->dev, spi->chip_select, "OLED_CHIP_SELECT");

189:     if (ret < 0)

190:         return ret;

191:     gpio_direction_output(spi->chip_select, 1);

192: #endif

193:

194:     ker_buf = kmalloc(4096, GFP_KERNEL);

195:

196:     /* 注册一个 file_operations */

197:     major = register_chrdev(0, "oled", &oled_ops);

198:

199:     class = class_create(THIS_MODULE, "oled");

200:

201:     /* 为了让mdev根据这些信息来创建设备节点 */

202:     device_create(class, NULL, MKDEV(major, 0), NULL, "oled"); /* /dev/oled */

203:

204:     return 0;

205: }

206:

207: static int spi_oled_remove(struct spi_device *spi)

208: {

209:     device_destroy(class, MKDEV(major, 0));

210:     class_destroy(class);

211:     unregister_chrdev(major, "oled");

212:

213:     kfree(ker_buf);

214:

215:     return 0;

216: }

217:

218: static struct spi_driver spi_oled_drv = {

219:     .driver = {

220:         .name    = "oled",

221:         .owner    = THIS_MODULE,

222:     },

223:     .probe        = spi_oled_probe,

224:     .remove        = spi_oled_remove,

225: };

226:

227: static int spi_oled_init(void)

228: {

229:     return spi_register_driver(&spi_oled_drv);

230: }

231:

232: static void spi_oled_exit(void)

233: {

234:     spi_unregister_driver(&spi_oled_drv);

235: }

236:

237: module_init(spi_oled_init);

238: module_exit(spi_oled_exit);

239: MODULE_DESCRIPTION("OLED SPI Driver");

240: MODULE_AUTHOR("[e-mail],www.100ask.net");

241: MODULE_LICENSE("GPL");

第187行，如果使用的是gpio模拟的spi的话，这个宏CONFIG_TQ2440_USE_SPI_GPIO会配置，这里我们使用的不是gpio模拟的，所以这个宏没有配置；

第182行，申请gpio，这里使用的函数是devm_gpio_request，它的好处是你不用再考虑gpio资源的释放了，系统会自动帮助你完成，类似的还有devm_kmalloc；

内核配置

System Type  --->

    SAMSUNG S3C24XX SoCs Support  --->

       [ ]   TQ2440 use spi gpio to communicate with peripherals

Device Drivers  --->

    [*] SPI support  --->

        <*>   Samsung S3C24XX series SPI

        <*>   Support TQ2440 OLED (from 100ask.com)

应用

1、oled_test.c

1: #include <stdlib.h>

2: #include <stdio.h>

3: #include <string.h>

4: #include <sys/types.h>

5: #include <sys/stat.h>

6: #include <fcntl.h>

7: #include <unistd.h>

8: #include <sys/ioctl.h>

9:

10: #include "oledfont.h"

11:

12: /* oled_test init

13:  * oled_test clear

14:  * oled_test clear <page>

15:  * oled_test <page> <col> <string>

16:  */

17:

18: #define OLED_CMD_INIT       0x100001

19: #define OLED_CMD_CLEAR_ALL  0x100002

20: #define OLED_CMD_CLEAR_PAGE 0x100003

21: #define OLED_CMD_SET_POS    0x100004

22:

23:

24:

25: /* page: 0-7

26:  * col : 0-127

27:  * 字符: 8x16象素

28:  */

29: void OLEDPutChar(int fd, int page, int col, char c)

30: {

31:     int i = 0;

32:     /* 得到字模 */

33:     const unsigned char *dots = oled_asc2_8x16[c - ' '];

34:

35:     /* 发给OLED */

36:     //OLEDSetPos(page, col);

37:     //ioctl(fd, OLED_CMD_CLEAR_PAGE, page);

38:     ioctl(fd, OLED_CMD_SET_POS, page | (col << 8));

39:     /* 发出8字节数据 */

40:     //for (i = 0; i < 8; i++)

41:     //    OLEDWriteDat(dots[i]);

42:     write(fd, &dots[0], 8);

43:

44:     //OLEDSetPos(page+1, col);

45:     //ioctl(fd, OLED_CMD_CLEAR_PAGE, page+1);

46:     ioctl(fd, OLED_CMD_SET_POS, (page+1) | (col << 8));

47:     /* 发出8字节数据 */

48:     //for (i = 0; i < 8; i++)

49:     //    OLEDWriteDat(dots[i+8]);

50:     write(fd, &dots[8], 8);

51: }

52:

53:

54:

55: /* page: 0-7

56:  * col : 0-127

57:  * 字符: 8x16象素

58:  */

59: void OLEDPrint(int fd, int page, int col, char *str)

60: {

61:     int i = 0;

62:

63:     ioctl(fd, OLED_CMD_CLEAR_PAGE, page);

64:     ioctl(fd, OLED_CMD_CLEAR_PAGE, page+1);

65:     while (str[i])

66:     {

67:         OLEDPutChar(fd, page, col, str[i]);

68:         col += 8;

69:         if (col > 127)

70:         {

71:             col = 0;

72:             page += 2;

73:             ioctl(fd, OLED_CMD_CLEAR_PAGE, page);

74:             ioctl(fd, OLED_CMD_CLEAR_PAGE, page+1);

75:         }

76:         i++;

77:     }

78: }

79:

80:

81: void print_usage(char *cmd)

82: {

83:     printf("Usage:\n");

84:     printf("%s init\n", cmd);

85:     printf("%s clear\n", cmd);

86:     printf("%s clear <page>\n", cmd);

87:     printf("%s <page> <col> <string>\n", cmd);

88:     printf("eg:\n");

89:     printf("%s 2 0 100ask.taobao.com\n", cmd);

90:     printf("page is 0,1,...,7\n");

91:     printf("col is 0,1,...,127\n");

92: }

93:

94: int main(int argc, char **argv)

95: {

96:     int do_init  = 0;

97:     int do_clear = 0;

98:     int do_show  = 0;

99:     int page = -1;

100:     int col;

101:

102:     int fd;

103:

104:     if (argc == 2 && !strcmp(argv[1], "init"))

105:         do_init = 1;

106:     if ((argc == 2) && !strcmp(argv[1], "clear"))

107:     {

108:         do_clear = 1;

109:     }

110:     if ((argc == 3) && !strcmp(argv[1], "clear"))

111:     {

112:         do_clear = 1;

113:         page = strtoul(argv[2], NULL, 0);

114:     }

115:     if (argc == 4)

116:     {

117:         do_show = 1;

118:         page = strtoul(argv[1], NULL, 0);

119:         col = strtoul(argv[2], NULL, 0);

120:     }

121:

122:     if (!do_init && !do_clear && !do_show)

123:     {

124:         print_usage(argv[0]);

125:         return -1;

126:     }

127:

128:     fd = open("/dev/oled", O_RDWR);

129:     if (fd < 0)

130:     {

131:         printf("can't open /dev/oled\n");

132:         return -1;

133:     }

134:

135:     if (do_init)

136:         ioctl(fd, OLED_CMD_INIT);

137:     else if (do_clear)

138:     {

139:         if (page == -1)

140:             ioctl(fd, OLED_CMD_CLEAR_ALL);

141:         else

142:         {

143:             if (page < 0 || page > 7)

144:             {

145:                 printf("page is 0,1,...,7\n");

146:                 return -1;

147:             }

148:             ioctl(fd, OLED_CMD_CLEAR_PAGE, page);

149:         }

150:     }

151:     else if (do_show)

152:     {

153:         if (page < 0 || page > 7)

154:         {

155:             printf("page is 0,1,...,7\n");

156:             return -1;

157:         }

158:         if (col < 0 || col > 127)

159:         {

160:             printf("col is 0,1,...,127\n");

161:             return -1;

162:         }

163:

164:         OLEDPrint(fd, page, col, argv[3]);

165:     }

166:     return 0;

167: }

168:

 

SPI驱动实现之软件控制器

一、驱动框架

​​​​

从图中可以看出，只替换了两个部分，在硬件上使用几个GPIO，不再使用SPI硬件控制器，所以在驱动上也需要做相应的变更，这部分在kernel中已经支持了。

二、代码

下面我们只列一下不同的部分。

SPI GPIO软件控制器

这里采用的也是platform架构。

1、platform_device

1: static struct spi_gpio_platform_data s3c_spi0_gpio_info = {

2:     .num_chipselect = S3C_GPIO_END,

3:     .miso        = S3C2410_GPE(11),

4:     .mosi        = S3C2410_GPE(12),

5:     .sck        = S3C2410_GPE(13),

6: };

7:

8: static struct platform_device s3c_device_spi0_gpio = {

9:     .name        = "spi_gpio",

10:     .id        = 0,

11:     .dev        = {

12:         .platform_data        = (void *)&s3c_spi0_gpio_info,

13:     }

14: };

15:

16: static struct platform_device *tq2440_devices[] __initdata = {

17: ......

18:     &s3c_device_spi0_gpio

19: };

20:

21: static void __init tq2440_machine_init(void)

22: {

23: ......

24:     platform_add_devices(tq2440_devices, ARRAY_SIZE(tq2440_devices));

25: ......

26: }

27:

28: MACHINE_START(TQ2440, "TQ2440")

29: ......

30:     .init_machine    = tq2440_machine_init,

31: ......

32: MACHINE_END

第3/4/5行，表示需要spi软件控制器需要使用的gpio引脚，至少需要MISO、SCK、MOSI；

第10行，表示模拟出的spi软件控制器的编号，也就是spi总线编号；

第9行，将来会跟驱动中的name进行匹配；

2、platform_driver

文件：drivers/spi/spi-gpio.c

1: #define DRIVER_NAME    "spi_gpio"

2: ......

3:

4: static struct platform_driver spi_gpio_driver = {

5:     .driver = {

6:         .name    = DRIVER_NAME,

7:         .owner    = THIS_MODULE,

8:         .of_match_table = of_match_ptr(spi_gpio_dt_ids),

9:     },

10:     .probe        = spi_gpio_probe,

11:     .remove        = spi_gpio_remove,

12: };

13: module_platform_driver(spi_gpio_driver);

 

OLED驱动

下面只列出需要注意的地方。

1、OLED板级信息

1: /* SPI OLED */

2: static struct spi_board_info tq2440_spi_board_info[] __initdata = {

3:     {

4:         .modalias    = "oled",

5:         .max_speed_hz    = 10000000,

6:         .bus_num    = 0,

7:         .mode        = SPI_MODE_0,

8:         .chip_select    = S3C2410_GPG(1),

9:         .platform_data    = (const void *)S3C2410_GPF(3),

10: #ifdef CONFIG_TQ2440_USE_SPI_GPIO

11:         .controller_data= (void *)S3C2410_GPG(1),

12: #endif

13:     },

14: };

第11行，这个表示片选信号，具体参见drivers/spi/spi-gpio.c的实现；

内核配置

System Type  --->

    SAMSUNG S3C24XX SoCs Support  --->

        [*]   TQ2440 use spi gpio to communicate with peripherals

Device Drivers  --->

    [*] SPI support  --->

        <*>   GPIO-based bitbanging SPI Master

        <*>   Support TQ2440 OLED (from 100ask.com) 

测试

编译app

arm-linux-gcc -Wall oled_test.c -o oled_test

操作

1: [root@TQ2440 sky]# ./oled_test init

2: [root@TQ2440 sky]# ./oled_test clear

3: [root@TQ2440 sky]# ./oled_test 0 0 "pengdonglin137"

4: [root@TQ2440 sky]#

结果(使用SPI驱动的两种实现方式的实验现象是一样的，只是驱动的内部实现机理不同)

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用Saleae16分析SPI时序

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上面我们在设置oled板级信息的时候将spi通信的速率设置为了10MHz，我在抓取spi波形的时候，遇到了问题。

现象如下：

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上面的图中，CLOCK时钟有些异常，可以看到只抓到7个波形，并且波形不是很均匀，出现很多类似的波形。刚开始我还以为spi控制器出问题了，后来发现，原来我把采样频率从16M提高到50M以后，全都正常了。

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我想就是采用率太低的可能，记得有一个香农采样定理，采样信号的频率至少应该是被采信号的两倍。为了印证这个看法，我又做了下面几个测试。

1、将采样频率设置为25M，通信速率为10M

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整个波形都没有问题。

2、将采样频率设置为16M，将通讯速率设置为7M

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可以看到，至少抓到的还是8个波形，还算正常。

因此，基本验证了我的看法。

 

完。