本教程基于TQ2440开发板来介绍嵌入式Linux的相关内容。
1. 开发板总览图
1.1 TQ2440核心板参数
| 特性 | 说明 |
|---|---|
| CPU处理器 | Samsung S3C2440AL，主频400MHz（最高可达533MHz） |
| SDRAM内存 | 板载64MB SDRAM |
| Nand Flash | 板载256MB Nand Flash（标准配置），掉电非易失 |
| Nor Flash | 板载2MB Nor Flash |
| CorePower | 专业1.25V核心电压供电，完美解决CPU发热现象 |
| Power | 核心板采用3.3V供电 |
| Powerled | 1个核心板电源指示灯 |
| 核心板接口 | 接口型号为DC-2.0双列直插 |
| 尺寸 | 37mm x 74mm |
1.2 TQ2440底板硬件参数
| 硬件特性 | 说明 |
|---|---|
| 串口 | 板载五线异步串行口（UART0），可外接串口扩展板引出另两个串口（UART1和UART2） |
| 网络接口 | 板载100M DM9000网卡，带联接和传输指示灯 |
| USB接口 | USB HOST接口；USB Device接口 |
| 存储接口 | 一个SD卡接口，支持32G SD卡 |
| 音频接口 | 采用芯片UDA1341，立体声音频输出，可录音 |
| LCD接口 | 集成了4线电阻式触摸屏接口；支持800×600、640×480、240×320、320×240等不同分辨率的TFT LCD |
| 摄像头接口 | 130W像素摄像头（标配驱动），支持AV信号视频输入或更高像素的摄像头 |
| 时钟源 | 内部实时时钟（带有后备锂电池） |
| 调试JTAG | JTAG接口，支持ADS1.2，keil等软件的单步调试功能 |
| 复位电路 | 采用专业复位芯片811进行复位，稳定可靠 |
| 电源接口 | 高电流带载的5V电源供电，带电源开关指示灯 |
| AD功能 | 可调电阻接到ADC引脚上用来验证模数转换 |
| IIC功能 | 提供AT24C02的EEPROM验证IIC功能 |
| 蜂鸣器 | 测试PWM功能的蜂鸣器 |
| 用户按键 | 4个用户按键，使用外部中断 |
| 用户LED灯 | 4个用户LED灯，使用GPIO口控制 |
| 底板尺寸 | 105mm×128mm |
1.3 电阻式触摸屏硬件参数
| 参数 | 说明 |
|---|---|
| 尺寸 | 4.3寸 |
| 显示面积 | 95.04（H）mm×53.86（V）mm |
| 显示颜色 | 16.7兆色 |
| 分辨率 | 480RGB×272（横屏） |
| 对比度 | 300:1 |
| 亮度 | 320cd/m2（流明） |
| 使用温度 | -20℃到70℃ |
| 次数 | 触摸屏使用次数超过100,000次 |
| 响应时间 | ≤10ms |
| 接口 | 40pin的0.5间距的FPC接口和50pin的2.0间距的插针接口 |
| 供电 | 提供5V和3.3V两种电压供电，缺省状态是3.3V |
| LCD驱动板的尺寸 | 103mm×83mm |
笔者说：
针对其它不同厂家的ARM9开发板，只要是采用S3C2440主芯片，则学习方法或者操作经验都是大同小异的；因为主芯片接口功能都是芯片设计时预定义好的，而开发板之所以不同，无非是开发板生产厂家配备的外设或多或少而已。所以，在学习的过程中，多思考，多总结，然后触类旁通。
2. TQ2440启动信息
代码
*** Warning - bad CRC or NAND, using default environment # EmbedSky BIOS for SKY2440/TQ2440 ##### Press Space key to Download Mode ! Booting Linux ... Copy linux kernel from 0x00200000 to 0x30008000, size = 0x00300000 ... Copy Kernel to SDRAM done,NOW, Booting Linux... Uncompressing Linux..........................done, booting the kernel. Linux version 2.6.30.4-EmbedSky (root@arthur-virtual-machine) (gcc version 4.3.3 (Sourcery G++ Lite 2009q1-176) ) #1 Fri Dec 14 11:15:24 CST 2012 CPU: ARM920T [41129200] revision 0 (ARMv4T), cr=c0007177 CPU: VIVT data cache, VIVT instruction cache Machine: TQ2440 ATAG_INITRD is deprecated; please update your bootloader. Memory policy: ECC disabled, Data cache writeback CPU S3C2440A (id 0x32440001) S3C24XX Clocks, (c) 2004 Simtec Electronics S3C244X: core 400.000 MHz, memory 100.000 MHz, peripheral 50.000 MHz CLOCK: Slow mode (1.500 MHz), fast, MPLL on, UPLL on Built 1 zonelists in Zone order, mobility grouping on. Total pages: 16256 Kernel command line: noinitrd root=/dev/mtdblock2 init=/linuxrc console=ttySAC0 NR_IRQS:85 irq: clearing subpending status 00000002 PID hash table entries: 256 (order: 8, 1024 bytes) Console: colour dummy device 80x30 console [ttySAC0] enabled Dentry cache hash table entries: 8192 (order: 3, 32768 bytes) Inode-cache hash table entries: 4096 (order: 2, 16384 bytes) Memory: 64MB = 64MB total Memory: 59664KB available (4512K code, 454K data, 240K init, 0K highmem) SLUB: Genslabs=11, HWalign=32, Order=0-3, MinObjects=0, CPUs=1, Nodes=1 Calibrating delay loop... 199.47 BogoMIPS (lpj=498688) Mount-cache hash table entries: 512 CPU: Testing write buffer coherency: ok net_namespace: 296 bytes NET: Registered protocol family 16 S3C2440: Initialising architecture S3C2440: IRQ Support S3C24XX DMA Driver, (c) 2003-2004,2006 Simtec Electronics DMA channel 0 at c4808000, irq 33 DMA channel 1 at c4808040, irq 34 DMA channel 2 at c4808080, irq 35 DMA channel 3 at c48080c0, irq 36 S3C244X: Clock Support, DVS off bio: create slab <bio-0> at 0 SCSI subsystem initialized usbcore: registered new interface driver usbfs usbcore: registered new interface driver hub usbcore: registered new device driver usb s3c2440-i2c s3c2440-i2c: slave address 0x10 s3c2440-i2c s3c2440-i2c: bus frequency set to 97 KHz s3c2440-i2c s3c2440-i2c: i2c-0: S3C I2C adapter cfg80211: Calling CRDA to update world regulatory domain NET: Registered protocol family 2 IP route cache hash table entries: 1024 (order: 0, 4096 bytes) TCP established hash table entries: 2048 (order: 2, 16384 bytes) TCP bind hash table entries: 2048 (order: 1, 8192 bytes) TCP: Hash tables configured (established 2048 bind 2048) TCP reno registered NET: Registered protocol family 1 yaffs Dec 14 2012 11:14:33 Installing. msgmni has been set to 116 alg: No test for stdrng (krng) io scheduler noop registered (default) Console: switching to colour frame buffer device 60x17 fb0: s3c2410fb frame buffer device bkl initialized led initialized beep initialized adc initialized s3c2440-uart.0: ttySAC0 at MMIO 0x50000000 (irq = 70) is a S3C2440 s3c2440-uart.1: ttySAC1 at MMIO 0x50004000 (irq = 73) is a S3C2440 s3c2440-uart.2: ttySAC2 at MMIO 0x50008000 (irq = 76) is a S3C2440 loop: module loaded Driver 'sd' needs updating - please use bus_type methods PPP generic driver version 2.4.2 PPP Deflate Compression module registered PPP BSD Compression module registered PPP MPPE Compression module registered NET: Registered protocol family 24 PPPoL2TP kernel driver, V1.0 dm9000 Ethernet Driver, V1.31 dm9000_set_io byte_width 4 dm9000_set_io byte_width 2 dm9000 revision 0x01 io_mode 00 Now use the default MAC address: 10:23:45:67:89:ab eth0 (dm9000): not using net_device_ops yet eth0: dm9000e at c4818000,c481c004 IRQ 51 MAC: 10:23:45:67:89:ab (EmbedSky) S3C24XX NAND Driver, (c) 2004 Simtec Electronics s3c2440-nand s3c2440-nand: Tacls=2, 20ns Twrph0=3 30ns, Twrph1=2 20ns NAND device: Manufacturer ID: 0xec, Chip ID: 0xda (Samsung NAND 256MiB 3,3V 8-bit) NAND_ECC_NONE selected by board driver. This is not recommended !! Scanning device for bad blocks Creating 3 MTD partitions on "NAND 256MiB 3,3V 8-bit": 0x000000000000-0x000000040000 : "EmbedSky_Board_uboot" 0x000000200000-0x000000500000 : "EmbedSky_Board_kernel" 0x000000500000-0x000010000000 : "EmbedSky_Board_yaffs2" ohci_hcd: USB 1.1 'Open' Host Controller (OHCI) Driver s3c2410-ohci s3c2410-ohci: S3C24XX OHCI s3c2410-ohci s3c2410-ohci: new USB bus registered, assigned bus number 1 s3c2410-ohci s3c2410-ohci: irq 42, io mem 0x49000000 ...... yaffs_read_super: isCheckpointed 0 VFS: Mounted root (yaffs filesystem) on device 31:2. Freeing init memory: 240K Start Qtopia-2.2.0 usbcore: registered new interface driver zd1211rw usbcore: registered new interface driver rt73usb rtusb init rt2870 ---> usbcore: registered new interface driver rt2870 Try to bring net interface up ... ifconfig eth0 hw ether 10:23:45:67:89:ab eth0: link down ifconfig eth0 192.168.1.6 netmask 255.255.255.0 up add default gw 192.168.1.2 Done [15/Mar/2001:01:21:27 +0000] Please press Enter to activate this console. boa: server version Boa/0.94.13 [15/Mar/2001:01:21:27 +0000] boa: server built Jul 29 2009 at 14:27:34. [15/Mar/2001:01:21:27 +0000] boa: starting server pid=641, port 80
3. 输出信息分析
从软件的角度可将嵌入式Linux分为四个层次，四个层次由低到高分为：引导加载程序、内核、文件系统、用户应用程序（可选）。
系统存储结构图：
3.1 引导加载程序
固化在固件中（firmware）的boot代码（可选）和Bootloader两部分。如下：
代码
# EmbedSky BIOS for SKY2440/TQ2440 ##### Press Space key to Download Mode ! Booting Linux ... Copy linux kernel from 0x00200000 to 0x30008000, size = 0x00300000 ... Copy Kernel to SDRAM done,NOW, Booting Linux... Uncompressing Linux..........................done, booting the kernel.
3.2 内核加载
定制的内核及控制内核引导系统的参数。如下：
代码
Linux version 2.6.30.4-EmbedSky (root@arthur-virtual-machine) (gcc version 4.3.3 (Sourcery G++ Lite 2009q1- 176) ) #1 Fri Dec 14 11:15:24 CST 2012 CPU: ARM920T [41129200] revision 0 (ARMv4T), cr=c0007177 CPU: VIVT data cache, VIVT instruction cache Machine: TQ2440 ATAG_INITRD is deprecated; please update your bootloader. Memory policy: ECC disabled, Data cache writeback CPU S3C2440A (id 0x32440001) S3C24XX Clocks, (c) 2004 Simtec Electronics S3C244X: core 400.000 MHz, memory 100.000 MHz, peripheral 50.000 MHz CLOCK: Slow mode (1.500 MHz), fast, MPLL on, UPLL on Built 1 zonelists in Zone order, mobility grouping on. Total pages: 16256 Kernel command line: noinitrd root=/dev/mtdblock2 init=/linuxrc console=ttySAC0 ...... yaffs_read_super: isCheckpointed 0 VFS: Mounted root (yaffs filesystem) on device 31:2. Freeing init memory: 240K
3.3 文件系统
实现文件存取、管理等功能的模块，提供一系列文件输入输出等文件管理功能，为嵌入式系统和设备提供文件系统支持。
代码
Start Qtopia-2.2.0 usbcore: registered new interface driver zd1211rw usbcore: registered new interface driver rt73usb rtusb init rt2870 ---> usbcore: registered new interface driver rt2870 Try to bring net interface up ... ifconfig eth0 hw ether 10:23:45:67:89:ab eth0: link down ifconfig eth0 192.168.1.6 netmask 255.255.255.0 up add default gw 192.168.1.2 Done [01/Jan/1970:00:00:07 +0000] boa: server version Boa/0.94.13 [01/Jan/1970:00:00:07 +0000] boa: server built Jul 29 2009 at 14:27:34. [01/Jan/1970:00:00:07 +0000] boa: starting server pid=643, port 80 Please press Enter to activate this console. eth0: link up, 100Mbps, full-duplex, lpa 0x4DE1
3.4 应用程序
启动开发板后，可以看到4.3寸LCD上显示的界面，有很多基于qt开发的测试应用，如下：****
至此，启动信息结构简略介绍完成，后续会在深入linux文章中将各个再部分详细介绍。
笔者说：
对于嵌入式linux，建议循环渐进式学习，先从整体上去把控系统结构，当对整体有了“框架”式认识后，再细细学习并多实践，去充实整个框架内的内容。这样，才会不至于在学习的过程中，因为有太多的困惑而丧气甚至放弃。