AM335x(TQ335x)学习笔记——挂载Ramdisk

上篇文章中我们已经能够通过u-boot启动内核了，但是没有能够启动成功，从内核的log中可以看出，内核启动失败的原因是没有挂载到root文件系统，本文将使用busybox制作根文件系统并打包成ramdisk供u-boot启动内核使用。

（1）制作根文件系统

使用busybox构建根文件系统的步骤可以参考本博客的另外一篇文章，该文章链接如下：

S5PV210(TQ210)学习笔记——内核移植与文件系统构建

需要补充的是，文章"S5PV210(TQ210)学习笔记——内核移植与文件系统构建"中记录rootfs文件系统构建时漏掉了一步，没有在etc/sysconfig/目录下创建HOSTNAME文件，可以手动添加HOSTNAME文件，其内容为主机名称，本文使用了tq335x。在rootfs目录可以通过如下指令创建：

echo tq335x > etc/sysconfig/HOSTNAME

本文在已制作好的rootfs基础上，制作ramdisk。

（2）制作ramdisk

制作ramdisk的方式很多，最方便的是使用指令genext2fs。ubuntu操作系统上可以通过apt-get工具直接安装genext2fs工具：

sudo apt-get install genext2fs

其它操作系统也有类似的管理工具，这里就不一一列举了，下面使用genext2fs打包rootfs目录。命令如下：

genext2fs -b 4096 -d rootfs/ ramdisk

然后使用gzip命令压缩ramdisk：

gzip -9 -f ramdisk

执行完成该命令后可以得到文件ramdisk.gz。

由于u-boot启动内核使用的ramdisk需要有u-boot的image头，故需要使用编译u-boot时生成的工具mkimage将ramdisk.gz制作为ramdisk.img。其中，工具mkimage位于u-boot的tools目录下，制作ramdisk.img的指令如下：

u-boot-2014.10/tools/mkimage -A arm -O linux -T ramdisk -C none -a 0x88080000 -n "ramdisk" -d ramdisk.gz ramdisk.img

命令中mkimage前的路径根据自己实际执行的路径指定即可。

这样，就完成了u-boot可以使用的ramdisk制作，然后将ramdisk.img拷贝到SD卡的boot目录下即可。

（3）挂载ramdisk

老式的ATAGS方式启动内核时使用ATAG传递bootargs给内核，由于本文使用的dtb方式启动内核，故采取dtb的chosen方式传递bootargs给内核。

Step1: 修改内核配置

make ARCH=arm menuconfig

进入配置项：

Boot options  --->

按N键取消配置项：

[ ] Use appended device tree blob to zImage (EXPERIMENTAL)

官方内核默认启用了该项配置。启用该项配置后内核兼容老式的ATAGS方式内核启动，关闭后则使用新式的dtb方式启动，故此处禁用了此项配置。

按ESC保存配置后退出menuconfig画面，重新编译内核：

make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- -j8

Step2:添加bootargs到dtb

切换到内核目录arch/arm/boot/dts/，拷贝am335x-evm.dts为tq335x.dts：

cp am335x-evm.dts tq335x.dts

打开tq335x.dts，在memory项后通过chosen方式添加bootargs，添加内容如下：

memory {
	device_type = "memory";
	reg = <0x80000000 0x10000000>; /* 256 MB */
};

chosen {
	bootargs = "console=ttyO0,115200n8 root=/dev/ram0";
};

...

其中chosen节点是新添加的，memory节点是原有的。

接下来重新编译dtb：

make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- tq335x.dtb

将新编译得到的tq335x.dtb拷贝到SD的boot目录下。至此，准备工作就完成了，下面我们使用新制作的ramdisk.img和tq335x.dtb启动内核。

Step3:使用新制作的ramdisk.img和tq335x.dtb启动内核

将SD插到开发板上，给开发板上电（开发板切换到SD卡启动模式），可以通过按任意键打断内核启动进入u-boot命令模式（由于之前没有配置u-boot的bootcmd环境变量，而默认的u-boot环境无法启动内核，故，开发板上电后不按键的话也会进入u-boot的命令行模式）。

首先是加载内核到DRAM：

load mmc 0 ${loadaddr} /boot/zImage

其中，${loadaddr}在u-boot的环境变量中默认指定为0x82000000，这里可以直接打数字。

然后是加载dtb到DRAM：

load mmc 0 ${fdtaddr} /boot/tq335x.dtb

${fdtaddr}的默认值是0x88000000。

接下来加载ramdisk到DRAM：

load mmc 0 ${rdaddr} /boot/ramdisk.img

${rdaddr}的默认值是0x88080000
最后就是将ramdisk和dtb的加载地址作为参数启动内核：

bootz ${loadaddr} ${rdaddr} ${fdtaddr}

至此，Linux内核已经能够正常启动并进入终端模式了。

启动Log如下：

Hit any key to stop autoboot:  0 
U-Boot# load mmc 0 ${fdtaddr} /boot/tq335x.dtb
34781 bytes read in 9 ms (3.7 MiB/s)
U-Boot# load mmc 0 ${loadaddr} /boot/zImage
4377824 bytes read in 242 ms (17.3 MiB/s)
U-Boot# load mmc 0 ${rdaddr} /boot/ramdisk.img
1120934 bytes read in 68 ms (15.7 MiB/s)
U-Boot# bootz ${loadaddr} ${rdaddr} ${fdtaddr}
Kernel image @ 0x82000000 [ 0x000000 - 0x42cce0 ]
## Loading init Ramdisk from Legacy Image at 88080000 ...
   Image Name:   ramdisk
   Created:      2014-11-18  15:47:41 UTC
   Image Type:   ARM Linux RAMDisk Image (uncompressed)
   Data Size:    1120870 Bytes = 1.1 MiB
   Load Address: 88080000
   Entry Point:  88080000
   Verifying Checksum ... OK
## Flattened Device Tree blob at 88000000
   Booting using the fdt blob at 0x88000000
   Loading Ramdisk to 8feee000, end 8ffffa66 ... OK
   Loading Device Tree to 8fee2000, end 8feed7dc ... OK


Starting kernel ...


[    0.000000] Booting Linux on physical CPU 0x0
[    0.000000] Linux version 3.17.2 (lilianrong@AY140721164813287e77Z) (gcc version 4.7.3 (Ubuntu/Linaro 4.7.3-12ubuntu1) ) #1 SMP Tue Nov 18 22:49:31 CST 2014
[    0.000000] CPU: ARMv7 Processor [413fc082] revision 2 (ARMv7), cr=10c5387d
[    0.000000] CPU: PIPT / VIPT nonaliasing data cache, VIPT aliasing instruction cache
[    0.000000] Machine model: TI AM335x EVM
[    0.000000] cma: Reserved 16 MiB at 9e800000
[    0.000000] Memory policy: Data cache writeback
[    0.000000]   HighMem zone: 1048574 pages exceeds freesize 0
[    0.000000] CPU: All CPU(s) started in SVC mode.
[    0.000000] AM335X ES2.1 (sgx neon )
[    0.000000] PERCPU: Embedded 9 pages/cpu @dfa9a000 s14336 r8192 d14336 u36864
[    0.000000] Built 1 zonelists in Zone order, mobility grouping on.  Total pages: 129792
[    0.000000] Kernel command line: console=ttyO0,115200n8 root=/dev/ram0
[    0.000000] PID hash table entries: 2048 (order: 1, 8192 bytes)
[    0.000000] Dentry cache hash table entries: 65536 (order: 6, 262144 bytes)
[    0.000000] Inode-cache hash table entries: 32768 (order: 5, 131072 bytes)
[    0.000000] Memory: 483692K/523264K available (5668K kernel code, 647K rwdata, 2208K rodata, 406K init, 8210K bss, 39572K reserved, 0K highmem)
[    0.000000] Virtual kernel memory layout:
[    0.000000]     vector  : 0xffff0000 - 0xffff1000   (   4 kB)
[    0.000000]     fixmap  : 0xffc00000 - 0xffe00000   (2048 kB)
[    0.000000]     vmalloc : 0xe0800000 - 0xff000000   ( 488 MB)
[    0.000000]     lowmem  : 0xc0000000 - 0xe0000000   ( 512 MB)
[    0.000000]     pkmap   : 0xbfe00000 - 0xc0000000   (   2 MB)
[    0.000000]     modules : 0xbf000000 - 0xbfe00000   (  14 MB)
[    0.000000]       .text : 0xc0008000 - 0xc07b9478   (7878 kB)
[    0.000000]       .init : 0xc07ba000 - 0xc081f800   ( 406 kB)
[    0.000000]       .data : 0xc0820000 - 0xc08c1d08   ( 648 kB)
[    0.000000]        .bss : 0xc08c1d08 - 0xc10c68e0   (8211 kB)
[    0.000000] Hierarchical RCU implementation.
[    0.000000]  RCU restricting CPUs from NR_CPUS=2 to nr_cpu_ids=1.
[    0.000000] RCU: Adjusting geometry for rcu_fanout_leaf=16, nr_cpu_ids=1
[    0.000000] NR_IRQS:16 nr_irqs:16 16
[    0.000000] IRQ: Found an INTC at 0xfa200000 (revision 5.0) with 128 interrupts
[    0.000000] Total of 128 interrupts on 1 active controller
[    0.000000] OMAP clockevent source: timer2 at 24000000 Hz
[    0.000013] sched_clock: 32 bits at 24MHz, resolution 41ns, wraps every 178956969942ns
[    0.000061] OMAP clocksource: timer1 at 24000000 Hz
[    0.000795] Console: colour dummy device 80x30
[    0.000847] Lock dependency validator: Copyright (c) 2006 Red Hat, Inc., Ingo Molnar
[    0.000856] ... MAX_LOCKDEP_SUBCLASSES:  8
[    0.000863] ... MAX_LOCK_DEPTH:          48
[    0.000870] ... MAX_LOCKDEP_KEYS:        8191
[    0.000878] ... CLASSHASH_SIZE:          4096
[    0.000885] ... MAX_LOCKDEP_ENTRIES:     32768
[    0.000892] ... MAX_LOCKDEP_CHAINS:      65536
[    0.000900] ... CHAINHASH_SIZE:          32768
[    0.000907]  memory used by lock dependency info: 5167 kB
[    0.000915]  per task-struct memory footprint: 1152 bytes
[    0.000956] Calibrating delay loop... 996.14 BogoMIPS (lpj=4980736)
[    0.079037] pid_max: default: 32768 minimum: 301
[    0.079438] Security Framework initialized
[    0.079564] Mount-cache hash table entries: 1024 (order: 0, 4096 bytes)
[    0.079576] Mountpoint-cache hash table entries: 1024 (order: 0, 4096 bytes)
[    0.081769] CPU: Testing write buffer coherency: ok
[    0.082962] CPU0: thread -1, cpu 0, socket -1, mpidr 0
[    0.083084] Setting up static identity map for 0x8055f030 - 0x8055f0a0
[    0.086327] Brought up 1 CPUs
[    0.086347] SMP: Total of 1 processors activated.
[    0.086357] CPU: All CPU(s) started in SVC mode.
[    0.088983] devtmpfs: initialized
[    0.097743] VFP support v0.3: implementor 41 architecture 3 part 30 variant c rev 3
[    0.132789] omap_hwmod: tptc0 using broken dt data from edma
[    0.133139] omap_hwmod: tptc1 using broken dt data from edma
[    0.133467] omap_hwmod: tptc2 using broken dt data from edma
[    0.141252] omap_hwmod: debugss: _wait_target_disable failed
[    0.198964] pinctrl core: initialized pinctrl subsystem
[    0.201633] regulator-dummy: no parameters
[    0.231057] NET: Registered protocol family 16
[    0.239540] DMA: preallocated 256 KiB pool for atomic coherent allocations
[    0.241725] cpuidle: using governor ladder
[    0.241754] cpuidle: using governor menu
[    0.253658] OMAP GPIO hardware version 0.1
[    0.268591] omap-gpmc 50000000.gpmc: could not find pctldev for node /pinmux@44e10800/nandflash_pins_s0, deferring probe
[    0.268635] platform 50000000.gpmc: Driver omap-gpmc requests probe deferral
[    0.273243] No ATAGs?
[    0.273274] hw-breakpoint: debug architecture 0x4 unsupported.
[    0.316650] edma-dma-engine edma-dma-engine.0: TI EDMA DMA engine driver
[    0.318001] vbat: 5000 mV 
[    0.318774] lis3_reg: no parameters
[    0.322209] SCSI subsystem initialized
[    0.323028] usbcore: registered new interface driver usbfs
[    0.323207] usbcore: registered new interface driver hub
[    0.327009] usbcore: registered new device driver usb
[    0.327877] omap_i2c 44e0b000.i2c: could not find pctldev for node /pinmux@44e10800/pinmux_i2c0_pins, deferring probe
[    0.327917] platform 44e0b000.i2c: Driver omap_i2c requests probe deferral
[    0.327972] omap_i2c 4802a000.i2c: could not find pctldev for node /pinmux@44e10800/pinmux_i2c1_pins, deferring probe
[    0.327995] platform 4802a000.i2c: Driver omap_i2c requests probe deferral
[    0.332363] Switched to clocksource timer1
[    0.477595] NET: Registered protocol family 2
[    0.479415] TCP established hash table entries: 4096 (order: 2, 16384 bytes)
[    0.479601] TCP bind hash table entries: 4096 (order: 5, 147456 bytes)
[    0.480965] TCP: Hash tables configured (established 4096 bind 4096)
[    0.481157] TCP: reno registered
[    0.481186] UDP hash table entries: 256 (order: 2, 20480 bytes)
[    0.481375] UDP-Lite hash table entries: 256 (order: 2, 20480 bytes)
[    0.482657] NET: Registered protocol family 1
[    0.484656] RPC: Registered named UNIX socket transport module.
[    0.484680] RPC: Registered udp transport module.
[    0.484690] RPC: Registered tcp transport module.
[    0.484699] RPC: Registered tcp NFSv4.1 backchannel transport module.
[    0.485566] Trying to unpack rootfs image as initramfs...
[    0.487045] rootfs image is not initramfs (no cpio magic); looks like an initrd
[    0.497016] Freeing initrd memory: 1092K (cfeee000 - cffff000)
[    0.497514] hw perfevents: enabled with armv7_cortex_a8 PMU driver, 5 counters available
[    0.501968] futex hash table entries: 256 (order: 2, 16384 bytes)
[    0.507634] VFS: Disk quotas dquot_6.5.2
[    0.507781] Dquot-cache hash table entries: 1024 (order 0, 4096 bytes)
[    0.510254] NFS: Registering the id_resolver key type
[    0.510637] Key type id_resolver registered
[    0.510653] Key type id_legacy registered
[    0.510794] jffs2: version 2.2. (NAND) (SUMMARY)  漏 2001-2006 Red Hat, Inc.
[    0.511229] msgmni has been set to 978
[    0.516624] io scheduler noop registered
[    0.516656] io scheduler deadline registered
[    0.516726] io scheduler cfq registered (default)
[    0.519057] pinctrl-single 44e10800.pinmux: 142 pins at pa f9e10800 size 568
[    0.522800] Serial: 8250/16550 driver, 4 ports, IRQ sharing enabled
[    0.528945] omap_uart 44e09000.serial: no wakeirq for uart0
[    0.529540] 44e09000.serial: ttyO0 at MMIO 0x44e09000 (irq = 88, base_baud = 3000000) is a OMAP UART0
[    1.236732] console [ttyO0] enabled
[    1.245368] omap_rng 48310000.rng: OMAP Random Number Generator ver. 20
[    1.277842] brd: module loaded
[    1.297230] loop: module loaded
[    1.303764] mtdoops: mtd device (mtddev=name/number) must be supplied
[    1.313662] usbcore: registered new interface driver asix
[    1.319456] usbcore: registered new interface driver ax88179_178a
[    1.326006] usbcore: registered new interface driver cdc_ether
[    1.332305] usbcore: registered new interface driver smsc95xx
[    1.338427] usbcore: registered new interface driver net1080
[    1.344489] usbcore: registered new interface driver cdc_subset
[    1.350791] usbcore: registered new interface driver zaurus
[    1.356854] usbcore: registered new interface driver cdc_ncm
[    1.364965] usbcore: registered new interface driver cdc_wdm
[    1.371056] usbcore: registered new interface driver usb-storage
[    1.377647] usbcore: registered new interface driver usbtest
[    1.388450] mousedev: PS/2 mouse device common for all mice
[    1.399599] omap_rtc 44e3e000.rtc: rtc core: registered 44e3e000.rtc as rtc0
[    1.407152] 44e3e000.rtc: already running
[    1.411995] i2c /dev entries driver
[    1.415787] Driver for 1-wire Dallas network protocol.
[    1.428670] omap_wdt: OMAP Watchdog Timer Rev 0x01: initial timeout 60 sec
[    1.438626] omap_hsmmc 48060000.mmc: unable to get vmmc regulator -517
[    1.446110] platform 48060000.mmc: Driver omap_hsmmc requests probe deferral
[    1.454198] ledtrig-cpu: registered to indicate activity on CPUs
[    1.461042] usbcore: registered new interface driver usbhid
[    1.466922] usbhid: USB HID core driver
[    1.472270] oprofile: using arm/armv7
[    1.476763] TCP: cubic registered
[    1.480243] Initializing XFRM netlink socket
[    1.484880] NET: Registered protocol family 17
[    1.489611] NET: Registered protocol family 15
[    1.494616] Key type dns_resolver registered
[    1.499266] omap_voltage_late_init: Voltage driver support not added
[    1.505960] sr_dev_init: No voltage domain specified for smartreflex0. Cannot initialize
[    1.514433] sr_dev_init: No voltage domain specified for smartreflex1. Cannot initialize
[    1.523926] ThumbEE CPU extension supported.
[    1.528444] Registering SWP/SWPB emulation handler
[    1.533522] SmartReflex Class3 initialized
[    1.547402] omap-gpmc 50000000.gpmc: GPMC revision 6.0
[    1.554563] nand: device found, Manufacturer ID: 0xec, Chip ID: 0xd3
[    1.561211] nand: Samsung NAND 1GiB 3,3V 8-bit
[    1.565966] nand: 1024MiB, SLC, page size: 2048, OOB size: 64
[    1.571968] nand: error: CONFIG_MTD_NAND_OMAP_BCH not enabled
[    1.578104] omap2-nand: probe of omap2-nand.0 failed with error -22
[    1.691744] tps65910 0-002d: No interrupt support, no core IRQ
[    1.709178] vrtc: 1800 mV 
[    1.712892] vrtc: supplied by vbat
[    1.719981] vio: at 1500 mV 
[    1.723353] vio: supplied by vbat
[    1.730169] vdd_mpu: 912 <--> 1312 mV at 1325 mV 
[    1.735377] vdd_mpu: supplied by vbat
[    1.742659] vdd_core: 912 <--> 1150 mV at 1137 mV 
[    1.747889] vdd_core: supplied by vbat
[    1.754583] vdd3: 5000 mV 
[    1.760090] vdig1: at 1800 mV 
[    1.763611] vdig1: supplied by vbat
[    1.769998] vdig2: at 1800 mV 
[    1.773480] vdig2: supplied by vbat
[    1.779839] vpll: at 1800 mV 
[    1.783256] vpll: supplied by vbat
[    1.789576] vdac: at 1800 mV 
[    1.792977] vdac: supplied by vbat
[    1.799236] vaux1: at 1800 mV 
[    1.802749] vaux1: supplied by vbat
[    1.809109] vaux2: at 3300 mV 
[    1.812606] vaux2: supplied by vbat
[    1.818973] vaux33: at 3300 mV 
[    1.822579] vaux33: supplied by vbat
[    1.829010] vmmc: 1800 <--> 3300 mV at 3300 mV 
[    1.834051] vmmc: supplied by vbat
[    1.840026] vbb: at 3000 mV 
[    1.843609] vbb: supplied by vbat
[    1.848858] omap_i2c 44e0b000.i2c: bus 0 rev0.11 at 400 kHz
[    1.862630] omap_i2c 4802a000.i2c: bus 1 rev0.11 at 100 kHz
[    1.972271] davinci_mdio 4a101000.mdio: davinci mdio revision 1.6
[    1.978680] davinci_mdio 4a101000.mdio: detected phy mask ffffffde
[    1.988850] libphy: 4a101000.mdio: probed
[    1.993152] davinci_mdio 4a101000.mdio: phy[0]: device 4a101000.mdio:00, driver unknown
[    2.001513] davinci_mdio 4a101000.mdio: phy[5]: device 4a101000.mdio:05, driver unknown
[    2.011094] cpsw 4a100000.ethernet: Detected MACID = c4:ed:ba:88:b5:e4
[    2.022260] input: volume_keys@0 as /devices/volume_keys@0/input/input0
[    2.032966] omap_rtc 44e3e000.rtc: setting system clock to 2000-01-01 00:00:00 UTC (946684800)
[    2.041988] sr_init: No PMIC hook to init smartreflex
[    2.047636] sr_init: platform driver register failed for SR
[    2.071187] lis3_reg: disabling
[    2.078305] RAMDISK: gzip image found at block 0
[    2.088654] mmc0: host does not support reading read-only switch. assuming write-enable.
[    2.114634] mmc0: new high speed SDHC card at address aaaa
[    2.124023] mmcblk0: mmc0:aaaa SL16G 14.8 GiB 
[    2.145511]  mmcblk0:
[    2.264995] VFS: Mounted root (ext2 filesystem) readonly on device 1:0.
[    2.273502] devtmpfs: mounted
[    2.277355] Freeing unused kernel memory: 404K (c07ba000 - c081f000)
----------mount all..........
----------Starting mdev......


Please press Enter to activate this console. 
@tq335x #ls
HOSTNAME    dev         lib         mnt         sbin        usr
bin         etc         linuxrc     proc        sys         var
boot        home        lost+found  root        tmp

（4）小结

到目前为止，已经能够成功启动内核了，接下来我们会在新内核的基础上添加tq335x板载驱动。

本文作者：girlkoo

本文链接：http://blog.csdn.net/girlkoo/article/details/41258583

本文在该文章制作好的rootfs基础上，制作ramdisk。