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在以前的文章《使用Buildroot与Qemu学习ARM linux IIC驱动》中，写到过使用qemu来模拟使用ARM Linux，那个时候借助的是buildroot，这次我们使用Yocto来做同样的事情。
使用Qemu的好处在于，当我们在开发Userspace的程序时，可以在没有硬件的情况下完成测试。
同时不像以前一样我们需要自己去编译qemu，这次我们使用Yocto编译出来的native qemu来模拟。省去了我们手动编译可能出现的问题。
这里的选择指的是，我们在local.conf中指定MACHINE变量的值。我将其分成两种：
以前我一直使用这个，但是这个模拟的是一个ARM9的处理器，各种外设功能不足，我们希望可以模拟一个更高ARM架构的SoC。
在Qemu的模拟中，据个人有限经验对不同的板子的模拟情况的了解，zynq在Qemu中有较好的支持。同时xilinx对此也有不少的文档，同时xilinx的一些板子的支持属于Qemu默认的测试与支持Machine，因此选择Xilinx的板子来模拟比较合适。
同时，我们关注的是ARM相关，因此使用Cortex-A9比较好，对此，我们选择xilinx-zynq-a9。
在我们的Host PC中如果安装了qemu-system-arm，那么我们可以看到其支持的板子里面是有这个板子的：
qemu-system-arm -M ? Supported machines are: versatileab ARM Versatile/AB (ARM926EJ-S) versatilepb ARM Versatile/PB (ARM926EJ-S) lm3s811evb Stellaris LM3S811EVB z2 Zipit Z2 (PXA27x) connex Gumstix Connex (PXA255) sx1 Siemens SX1 (OMAP310) V2 realview-eb ARM RealView Emulation Baseboard (ARM926EJ-S) cubieboard cubietech cubieboard vexpress-a9 ARM Versatile Express for Cortex-A9 lm3s6965evb Stellaris LM3S6965EVB realview-pbx-a9 ARM RealView Platform Baseboard Explore for Cortex-A9 musicpal Marvell 88w8618 / MusicPal (ARM926EJ-S) mainstone Mainstone II (PXA27x) terrier Terrier PDA (PXA270) n810 Nokia N810 tablet aka. RX-44 (OMAP2420) <span style="color:#ff6666;">xilinx-zynq-a9 Xilinx Zynq Platform Baseboard for Cortex-A9</span> nuri Samsung NURI board (Exynos4210) realview-eb-mpcore ARM RealView Emulation Baseboard (ARM11MPCore) verdex Gumstix Verdex (PXA270) spitz Spitz PDA (PXA270) canon-a1100 Canon PowerShot A1100 IS akita Akita PDA (PXA270) smdkc210 Samsung SMDKC210 board (Exynos4210) integratorcp ARM Integrator/CP (ARM926EJ-S) sx1-v1 Siemens SX1 (OMAP310) V1 kzm ARM KZM Emulation Baseboard (ARM1136) highbank Calxeda Highbank (ECX-1000) n800 Nokia N800 tablet aka. RX-34 (OMAP2420) collie Collie PDA (SA-1110) realview-pb-a8 ARM RealView Platform Baseboard for Cortex-A8 vexpress-a15 ARM Versatile Express for Cortex-A15 none empty machine cheetah Palm Tungsten|E aka. Cheetah PDA (OMAP310) tosa Tosa PDA (PXA255) midway Calxeda Midway (ECX-2000) virt ARM Virtual Machine borzoi Borzoi PDA (PXA270)
先根据官方的step1到step6来编译出需要的image。需要注意的是我们这里使用单核的A9，因此machine应该为qemuzynq，即在local.conf中应该为：
# This sets the default machine to be qemux86 if no other machine is selected: MACHINE ??= "qemuzynq"
这个machine的定义位于其layer中的config中：
$ ls ../meta-xilinx/conf/machine/ -l total 52 drwxrwxr-x 11 hexiongjun hexiongjun 4096 May 16 10:38 boards -rw-rw-r-- 1 hexiongjun hexiongjun 593 May 16 10:38 ep108-zynqmp.conf drwxrwxr-x 3 hexiongjun hexiongjun 4096 May 16 10:38 include -rw-rw-r-- 1 hexiongjun hexiongjun 1049 May 16 10:38 kc705-trd-microblazeel.conf -rw-rw-r-- 1 hexiongjun hexiongjun 623 May 16 10:38 microzed-zynq7.conf -rw-rw-r-- 1 hexiongjun hexiongjun 804 May 16 10:38 picozed-zynq7.conf -rw-rw-r-- 1 hexiongjun hexiongjun 564 May 16 10:16 qemumicroblaze.conf -rw-rw-r-- 1 hexiongjun hexiongjun 512 May 16 10:16 qemumicroblaze-s3adsp1800.conf -rw-rw-r-- 1 hexiongjun hexiongjun 496 May 16 10:38 qemuzynq.conf -rw-rw-r-- 1 hexiongjun hexiongjun 1059 May 16 10:38 zc702-zynq7.conf -rw-rw-r-- 1 hexiongjun hexiongjun 1008 May 16 10:38 zc706-zynq7.conf -rw-rw-r-- 1 hexiongjun hexiongjun 847 May 16 10:38 zedboard-zynq7.conf -rw-rw-r-- 1 hexiongjun hexiongjun 627 May 16 10:38 zybo-zynq7.conf
IMAGE_FSTYPES = "jffs2 tar.bz2 cpio"
否则我们在后面的qemu中指定initrd的时候无法指定。
至此，我们就准备好了所有的材料。
直接使用runqemu即可：
$ runqemu qemuzynq Continuing with the following parameters: KERNEL: [/home/hexiongjun/EmbProj/am335X_Yocto/qemuzynq/tmp/deploy/images/qemuzynq/uImage] ROOTFS: [/home/hexiongjun/EmbProj/am335X_Yocto/qemuzynq/tmp/deploy/images/qemuzynq/core-image-minimal-qemuzynq-20160516035635.rootfs.cpio] FSTYPE: [cpio] Setting up tap interface under sudo Acquiring lockfile for tap0... Running qemu-system-arm... /home/hexiongjun/EmbProj/am335X_Yocto/qemuzynq/tmp/sysroots/x86_64-linux/usr/bin/qemu-system-arm -kernel /home/hexiongjun/EmbProj/am335X_Yocto/qemuzynq/tmp/deploy/images/qemuzynq/uImage -net nic,model=virtio -net tap,vlan=0,ifname=tap0,script=no,downscript=no -M xilinx-zynq-a9 -serial null -serial mon:stdio -dtb /home/hexiongjun/EmbProj/am335X_Yocto/qemuzynq/tmp/deploy/images/qemuzynq/uImage-qemuzynq.dtb -initrd /home/hexiongjun/EmbProj/am335X_Yocto/qemuzynq/tmp/deploy/images/qemuzynq/core-image-minimal-qemuzynq-20160516035635.rootfs.cpio -no-reboot -m 1024 --append "earlyprintk root=/dev/ram rw ip=192.168.7.2::192.168.7.1:255.255.255.0 mem=1024M " qemu-system-arm: Unsupported NIC model: virtio Set 'tap0' nonpersistent Releasing lockfile of preconfigured tap device 'tap0'
对此，有多种处理方法，最为简单的是我们直接使用qemu至此的 NIC model即可，因此先查询一下：
$ /home/hexiongjun/EmbProj/am335X_Yocto/qemuzynq/tmp/sysroots/x86_64-linux/usr/bin/qemu-system-arm -M xilinx-zynq-a9 -net nic,model=? qemu: Supported NIC models: cadence_gem
runqemu的脚本位于：
poky/scripts/runqemu-internal中，在里面我们可以看到其指定了NIC model，因此我们将其改成cadence_gem即可：
KERNEL_NETWORK_CMD="ip=192.168.7.$n2::192.168.7.$n1:255.255.255.0"
QEMU_TAP_CMD="-net tap,vlan=0,ifname=$TAP,script=no,downscript=no"
if [ "$VHOST_ACTIVE" = "yes" ]; then
QEMU_NETWORK_CMD="-net nic,model=<span style="color:#ff6666;">virtio</span> $QEMU_TAP_CMD,vhost=on"
else
QEMU_NETWORK_CMD="-net nic,model=<span style="color:#ff6666;">virtio</span> $QEMU_TAP_CMD"
fi
$ runqemu qemuzynq Continuing with the following parameters: KERNEL: [/home/hexiongjun/EmbProj/am335X_Yocto/qemuzynq/tmp/deploy/images/qemuzynq/uImage] ROOTFS: [/home/hexiongjun/EmbProj/am335X_Yocto/qemuzynq/tmp/deploy/images/qemuzynq/core-image-minimal-qemuzynq-20160516035635.rootfs.cpio] FSTYPE: [cpio] Setting up tap interface under sudo Acquiring lockfile for tap0... Running qemu-system-arm... /home/hexiongjun/EmbProj/am335X_Yocto/qemuzynq/tmp/sysroots/x86_64-linux/usr/bin/qemu-system-arm -kernel /home/hexiongjun/EmbProj/am335X_Yocto/qemuzynq/tmp/deploy/images/qemuzynq/uImage -net nic,model=cadence_gem -net tap,vlan=0,ifname=tap0,script=no,downscript=no -M xilinx-zynq-a9 -serial null -serial mon:stdio -dtb /home/hexiongjun/EmbProj/am335X_Yocto/qemuzynq/tmp/deploy/images/qemuzynq/uImage-qemuzynq.dtb -initrd /home/hexiongjun/EmbProj/am335X_Yocto/qemuzynq/tmp/deploy/images/qemuzynq/core-image-minimal-qemuzynq-20160516035635.rootfs.cpio -no-reboot -m 1024 --append "earlyprintk root=/dev/ram rw ip=192.168.7.2::192.168.7.1:255.255.255.0 mem=1024M " Warning: nic cadence_gem.1 has no peer [ 0.000000] Booting Linux on physical CPU 0x0 [ 0.000000] Linux version 3.19.0-xilinx (hexiongjun@hexiongjun-9020) (gcc version 5.2.0 (GCC) ) #1 SMP PREEMPT Mon May 16 11:54:40 CST 2016 [ 0.000000] CPU: ARMv7 Processor [413fc090] revision 0 (ARMv7), cr=10c5387d [ 0.000000] CPU: PIPT / VIPT nonaliasing data cache, VIPT nonaliasing instruction cache [ 0.000000] Machine model: xilinx-zynq-a9 [ 0.000000] Memory policy: Data cache writeback [ 0.000000] CPU: All CPU(s) started in SVC mode. [ 0.000000] PERCPU: Embedded 9 pages/cpu @eefd8000 s8128 r8192 d20544 u36864 [ 0.000000] Built 1 zonelists in Zone order, mobility grouping on. Total pages: 260624 [ 0.000000] Kernel command line: earlyprintk root=/dev/ram rw ip=192.168.7.2::192.168.7.1:255.255.255.0 mem=1024M [ 0.000000] PID hash table entries: 4096 (order: 2, 16384 bytes) [ 0.000000] Dentry cache hash table entries: 131072 (order: 7, 524288 bytes) [ 0.000000] Inode-cache hash table entries: 65536 (order: 6, 262144 bytes) [ 0.000000] Memory: 1028324K/1048576K available (4457K kernel code, 234K rwdata, 1408K rodata, 220K init, 198K bss, 20252K reserved, 0K cma-reserved, 270336K highmem) [ 0.000000] Virtual kernel memory layout: [ 0.000000] vector : 0xffff0000 - 0xffff1000 ( 4 kB) [ 0.000000] fixmap : 0xffc00000 - 0xfff00000 (3072 kB) [ 0.000000] vmalloc : 0xf0000000 - 0xff000000 ( 240 MB) [ 0.000000] lowmem : 0xc0000000 - 0xef800000 ( 760 MB) [ 0.000000] pkmap : 0xbfe00000 - 0xc0000000 ( 2 MB) [ 0.000000] modules : 0xbf000000 - 0xbfe00000 ( 14 MB) [ 0.000000] .text : 0xc0008000 - 0xc05c28f4 (5867 kB) [ 0.000000] .init : 0xc05c3000 - 0xc05fa000 ( 220 kB) [ 0.000000] .data : 0xc05fa000 - 0xc06349e0 ( 235 kB) [ 0.000000] .bss : 0xc06349e0 - 0xc0666470 ( 199 kB) [ 0.000000] Preemptible hierarchical RCU implementation. [ 0.000000] RCU restricting CPUs from NR_CPUS=4 to nr_cpu_ids=2.
输入Ctrl + A C，并输入q回车即可，Ctrl+C是无法退出的。
所有的工具有：
$ runqemu runqemu runqemu-addptable2image runqemu-export-rootfs runqemu-extract-sdk
runqemu-gen-tapdevs runqemu-ifdown runqemu-ifup runqemu-internal
参考
http://www.wiki.xilinx.com/QEMU
http://zedboard.org/content/qemu-deep-dive-0
https://lists.gnu.org/archive/html/qemu-devel/2015-10/msg00755.html
Yocto tips (20): Yocto中qemu模拟器的使用,以zynq Cortex-A9为例
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原文地址：http://blog.csdn.net/sy373466062/article/details/51424855
