Xen ARM with Virtualization Extensions/Vexpress

== Preparing the board ==
* We recommend disabling the A7 cpus by editing the board.txt file under the SITE directory corresponding to your Cortex A15 daughterboard:
 SCC: 0x018 0x00001FFF ;Reset control - (CA7s reset, CA15s running) - uncomment this to hold A7 cluster in 
* With recent firmware (newer than boot monitor V5.1.9), the Versatile Express can use multiple ways to bring up secondary cpus. Xen only supports sys_flags bring up. To select this mode, you need to set the bit[12] of SCC: 0x700 to 0. For instance:
 ** Before:
 SCC: 0x700 0x0032F003
 ** After:
 SCC: 0x700 0x0032E003
== Booting Xen and dom0 ==
=== Booting with U-Boot ===
The current approach requires tftp but it can be easily modify to load the different images from the mmc.
==== Build and flash U-Boot ====
Theses steps will programme U-Boot into NOR flash.
1) Clone U-Boot from the official repository (tested with v2013.10-rc2 tag)
 git clone git://git.denx.de/u-boot.git u-boot
 cd u-boot
 git checkout v2013.10
2) Build U-Boot for the versatile express
 make ARCH=arm CROSS_COMPILE=arm-unknown-linux-gnueabi- vexpress_ca15_tc2
3) Copy u-boot.bin from the root of the repository to the SOFTWARE directory of the firmware disk, giving it the name uboot.bin
 cp u-boot.bin /media/VEMSD/SOFTWARE/uboot.bin
The arm-unknown-linux-gnueabi compiler can be retrieved from kernel.org.
4) Add U-Boot image at the end of /media/VEMSD/SITE1/HBI0249A/images.txt
 NOR4UPDATE: AUTO ;IMAGE UPDATE:NONE/AUTO/FORCE
 NOR4ADDRESS: 00000000 ;Image Flash Address
 NOR4FILE: \SOFTWARE\uboot.bin ;Image File Name - master initrd
 NOR4LOAD: 80800000 ;Image Load Address
 NOR4ENTRY: 80800000 ;Image Entry Point
The TOTALIMAGES: line in the file will also need updating to account for this extra image and the 'NOR4' lines added may need to have a different number to '4' if that is not the next in sequence. 
5) If you want to let the board to automatically boot into U-Boot (and by extension Xen), then:
* Look for the name of the BOOTSCRIPT image in the file you edited in the previous step; this should be \SOFTWARE\booscr.txt.
* Edit this bootscript file to have the line:
 flash run uboot
==== Set up U-Boot to boot via PXE ====
The following script allow U-boot to download everything via tftp and boot xen.
* Copy xen, linux and the device tree in your tftp directory on your server (we assume /tftpboot until the end).
* Copy the script in /tftpboot
 wget http://xenbits.xen.org/people/julieng/load-xen-tftp.scr.txt
 mkimage -T script -C none -d load-xen-tftp.scr.txt /tftpboot/load-xen-tftp.img
* At U-Boot prompt, on your board, you need to set the following variable:
 setenv ipaddr 10.y.y.y
 setenv serverip 10.x.x.x
 setenv usbethaddr 00:zz:zz:zz:zz:zz
 setenv ethaddr 00:zz:zz:zz:zz:zz
 setenv xen_addr_r 0x80400000
 setenv kernel_addr_r 0xa0008000
 setenv dtb_addr_r 0x81f00000
 setenv script_addr_r 0x81000000
 setenv xen_bootargs 'sync_console console=dtuart dtuart=serial0'
 setenv dom0_bootargs 'console=hvc0,38400 debug ignore_loglevel root=/dev/mmcblk0p2'
 setenv bootcmd 'tftpboot $script_addr_r $serverip:/load-xen-tftp.img; source $script_addr_r'
 setenv kernel_path /linux-zImage
 setenv xen_path /xen-uImage
 setenv dtb_path /vexpress-v2p-ca15_a7.dtb
with:
* 10.y.y.y the ip addr of the board
* 10.x.x.x the ip of a tftp server (or PXE server).
* 00:zz:zz:zz:zz:zz the MAC address of the board.
* /linux-zImage the path to the Linux kernel. It should be placed to /tftpboot/linux-zImage on your server
* /xen-uImage the path to Xen uImage. It should be placed to /tftpboot/xen-uImage on your server. You can create the uImage with
 mkimage -A arm -T kernel -a 0x80200000 -e 0x80200000 -C none -d $xen_root/xen/xen /tftpboot/xen-uImage
* /vexpress-v2p-ca15_a7.dtb the path to the device tree. It should be placed /tftpboot/vexpress-v2p-ca15_a7.dtb
=== Booting without U-Boot ===
This solution requires to modify the firmware configuration. The support will be removed soon because Xen will require all CPU to boot in hypervisor mode. We advice to the use the U-Boot solution (see above).
If you are trying to run Xen on a Versatile Express Cortex A15 machine, you might want to copy xen (the Xen binary output, xen.git/xen/xen) and the Linux Dom0 zImage to the SOFTWARE directory and add the two following stanzas to your images.txt file:
 NOR3UPDATE: AUTO ;IMAGE UPDATE:NONE/AUTO/FORCE
 NOR3ADDRESS: 0c000000 ;Image Flash Address
 NOR3FILE: \SOFTWARE\Xen\xen ;Image File Name
 NOR3LOAD: 80200000 ;Image Load Address
 NOR3ENTRY: 80200000 ;Image Entry Point
 
 NOR4UPDATE: AUTO ;IMAGE UPDATE:NONE/AUTO/FORCE
 NOR4ADDRESS: 000c0000 ;Image Flash Address
 NOR4FILE: \SOFTWARE\Xen\zImage ;Image File Name
 NOR4LOAD: 80008000 ;Image Load Address
 NOR4ENTRY: 80008000 ;Image Entry Point
* Note that before commit 47d1a51 (xen: arm: make zImage the default target which we install) it was necessary to use xen.git/xen/xen.bin for NOR3FILE instead of xen.git/xen/xen.
* The address of the Dom0 kernel in Flash at the moment is not configurable, it is defined as KERNEL_FLASH_ADDRESS in Xen. On a Versatile Express machine this address can be determined by executing flash list images from the boot manager. You'll have to manually change it.
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