基于TQ2440的SPI驱动学习（OLED）

平台简介

开发板：TQ2440 （NandFlash：256M  内存：64M）

u-boot版本：u-boot-2015.04

内核版本：Linux-3.14

作者：彭东林

邮箱：pengdonglin137@163.com

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：git@code.csdn.net: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

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("weidongshan@qq.com,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)

用Saleae16分析SPI时序

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：

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。

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

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

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。