Move this out of the main file since for simple users it is easier to rely on standard boot.
Signed-off-by: Simon Glass sjg@chromium.org ---
(no changes since v2)
Changes in v2: - Add new patch
doc/arch/x86/index.rst | 1 + doc/arch/x86/manual_boot.rst | 276 +++++++++++++++++++++++++++++++++++ doc/arch/x86/x86.rst | 272 +--------------------------------- 3 files changed, 280 insertions(+), 269 deletions(-) create mode 100644 doc/arch/x86/manual_boot.rst
diff --git a/doc/arch/x86/index.rst b/doc/arch/x86/index.rst index 3dc19d603d4c..69db0a5d6489 100644 --- a/doc/arch/x86/index.rst +++ b/doc/arch/x86/index.rst @@ -9,3 +9,4 @@ x86 :maxdepth: 2
x86 + manual_boot diff --git a/doc/arch/x86/manual_boot.rst b/doc/arch/x86/manual_boot.rst new file mode 100644 index 000000000000..ec069f2c3972 --- /dev/null +++ b/doc/arch/x86/manual_boot.rst @@ -0,0 +1,276 @@ +Booting Ubuntu Manually +----------------------- + +This shows a manual approach to booting Ubuntu without standard boot or the EFI +interface. + +As an example of how to set up your boot flow with U-Boot, here are +instructions for starting Ubuntu from U-Boot. These instructions have been +tested on Minnowboard MAX with a SATA drive but are equally applicable on +other platforms and other media. There are really only four steps and it's a +very simple script, but a more detailed explanation is provided here for +completeness. + +Note: It is possible to set up U-Boot to boot automatically using syslinux. +It could also use the grub.cfg file (/efi/ubuntu/grub.cfg) to obtain the +GUID. If you figure these out, please post patches to this README. + +Firstly, you will need Ubuntu installed on an available disk. It should be +possible to make U-Boot start a USB start-up disk but for now let's assume +that you used another boot loader to install Ubuntu. + +Use the U-Boot command line to find the UUID of the partition you want to +boot. For example our disk is SCSI device 0:: + + => part list scsi 0 + + Partition Map for SCSI device 0 -- Partition Type: EFI + + Part Start LBA End LBA Name + Attributes + Type GUID + Partition GUID + 1 0x00000800 0x001007ff "" + attrs: 0x0000000000000000 + type: c12a7328-f81f-11d2-ba4b-00a0c93ec93b + guid: 9d02e8e4-4d59-408f-a9b0-fd497bc9291c + 2 0x00100800 0x037d8fff "" + attrs: 0x0000000000000000 + type: 0fc63daf-8483-4772-8e79-3d69d8477de4 + guid: 965c59ee-1822-4326-90d2-b02446050059 + 3 0x037d9000 0x03ba27ff "" + attrs: 0x0000000000000000 + type: 0657fd6d-a4ab-43c4-84e5-0933c84b4f4f + guid: 2c4282bd-1e82-4bcf-a5ff-51dedbf39f17 + => + +This shows that your SCSI disk has three partitions. The really long hex +strings are called Globally Unique Identifiers (GUIDs). You can look up the +'type' ones `here`_. On this disk the first partition is for EFI and is in +VFAT format (DOS/Windows):: + + => fatls scsi 0:1 + efi/ + + 0 file(s), 1 dir(s) + + +Partition 2 is 'Linux filesystem data' so that will be our root disk. It is +in ext2 format:: + + => ext2ls scsi 0:2 + <DIR> 4096 . + <DIR> 4096 .. + <DIR> 16384 lost+found + <DIR> 4096 boot + <DIR> 12288 etc + <DIR> 4096 media + <DIR> 4096 bin + <DIR> 4096 dev + <DIR> 4096 home + <DIR> 4096 lib + <DIR> 4096 lib64 + <DIR> 4096 mnt + <DIR> 4096 opt + <DIR> 4096 proc + <DIR> 4096 root + <DIR> 4096 run + <DIR> 12288 sbin + <DIR> 4096 srv + <DIR> 4096 sys + <DIR> 4096 tmp + <DIR> 4096 usr + <DIR> 4096 var + <SYM> 33 initrd.img + <SYM> 30 vmlinuz + <DIR> 4096 cdrom + <SYM> 33 initrd.img.old + => + +and if you look in the /boot directory you will see the kernel:: + + => ext2ls scsi 0:2 /boot + <DIR> 4096 . + <DIR> 4096 .. + <DIR> 4096 efi + <DIR> 4096 grub + 3381262 System.map-3.13.0-32-generic + 1162712 abi-3.13.0-32-generic + 165611 config-3.13.0-32-generic + 176500 memtest86+.bin + 178176 memtest86+.elf + 178680 memtest86+_multiboot.bin + 5798112 vmlinuz-3.13.0-32-generic + 165762 config-3.13.0-58-generic + 1165129 abi-3.13.0-58-generic + 5823136 vmlinuz-3.13.0-58-generic + 19215259 initrd.img-3.13.0-58-generic + 3391763 System.map-3.13.0-58-generic + 5825048 vmlinuz-3.13.0-58-generic.efi.signed + 28304443 initrd.img-3.13.0-32-generic + => + +The 'vmlinuz' files contain a packaged Linux kernel. The format is a kind of +self-extracting compressed file mixed with some 'setup' configuration data. +Despite its size (uncompressed it is >10MB) this only includes a basic set of +device drivers, enough to boot on most hardware types. + +The 'initrd' files contain a RAM disk. This is something that can be loaded +into RAM and will appear to Linux like a disk. Ubuntu uses this to hold lots +of drivers for whatever hardware you might have. It is loaded before the +real root disk is accessed. + +The numbers after the end of each file are the version. Here it is Linux +version 3.13. You can find the source code for this in the Linux tree with +the tag v3.13. The '.0' allows for additional Linux releases to fix problems, +but normally this is not needed. The '-58' is used by Ubuntu. Each time they +release a new kernel they increment this number. New Ubuntu versions might +include kernel patches to fix reported bugs. Stable kernels can exist for +some years so this number can get quite high. + +The '.efi.signed' kernel is signed for EFI's secure boot. U-Boot has its own +secure boot mechanism - see `this`_ & `that`_. It cannot read .efi files +at present. + +To boot Ubuntu from U-Boot the steps are as follows: + +1. Set up the boot arguments. Use the GUID for the partition you want to boot:: + + => setenv bootargs root=/dev/disk/by-partuuid/965c59ee-1822-4326-90d2-b02446050059 ro + +Here root= tells Linux the location of its root disk. The disk is specified +by its GUID, using '/dev/disk/by-partuuid/', a Linux path to a 'directory' +containing all the GUIDs Linux has found. When it starts up, there will be a +file in that directory with this name in it. It is also possible to use a +device name here, see later. + +2. Load the kernel. Since it is an ext2/4 filesystem we can do:: + + => ext2load scsi 0:2 03000000 /boot/vmlinuz-3.13.0-58-generic + +The address 30000000 is arbitrary, but there seem to be problems with using +small addresses (sometimes Linux cannot find the ramdisk). This is 48MB into +the start of RAM (which is at 0 on x86). + +3. Load the ramdisk (to 64MB):: + + => ext2load scsi 0:2 04000000 /boot/initrd.img-3.13.0-58-generic + +4. Start up the kernel. We need to know the size of the ramdisk, but can use + a variable for that. U-Boot sets 'filesize' to the size of the last file it + loaded:: + + => zboot 03000000 0 04000000 ${filesize} + +Type 'help zboot' if you want to see what the arguments are. U-Boot on x86 is +quite verbose when it boots a kernel. You should see these messages from +U-Boot:: + + Valid Boot Flag + Setup Size = 0x00004400 + Magic signature found + Using boot protocol version 2.0c + Linux kernel version 3.13.0-58-generic (buildd@allspice) #97-Ubuntu SMP Wed Jul 8 02:56:15 UTC 2015 + Building boot_params at 0x00090000 + Loading bzImage at address 100000 (5805728 bytes) + Magic signature found + Initial RAM disk at linear address 0x04000000, size 19215259 bytes + Kernel command line: "root=/dev/disk/by-partuuid/965c59ee-1822-4326-90d2-b02446050059 ro" + + Starting kernel ... + +U-Boot prints out some bootstage timing. This is more useful if you put the +above commands into a script since then it will be faster:: + + Timer summary in microseconds: + Mark Elapsed Stage + 0 0 reset + 241,535 241,535 board_init_r + 2,421,611 2,180,076 id=64 + 2,421,790 179 id=65 + 2,428,215 6,425 main_loop + 48,860,584 46,432,369 start_kernel + + Accumulated time: + 240,329 ahci + 1,422,704 vesa display + +Now the kernel actually starts (if you want to examine kernel boot up message on +the serial console, append "console=ttyS0,115200" to the kernel command line):: + + [ 0.000000] Initializing cgroup subsys cpuset + [ 0.000000] Initializing cgroup subsys cpu + [ 0.000000] Initializing cgroup subsys cpuacct + [ 0.000000] Linux version 3.13.0-58-generic (buildd@allspice) (gcc version 4.8.2 (Ubuntu 4.8.2-19ubuntu1) ) #97-Ubuntu SMP Wed Jul 8 02:56:15 UTC 2015 (Ubuntu 3.13.0-58.97-generic 3.13.11-ckt22) + [ 0.000000] Command line: root=/dev/disk/by-partuuid/965c59ee-1822-4326-90d2-b02446050059 ro console=ttyS0,115200 + +It continues for a long time. Along the way you will see it pick up your +ramdisk:: + + [ 0.000000] RAMDISK: [mem 0x04000000-0x05253fff] + ... + [ 0.788540] Trying to unpack rootfs image as initramfs... + [ 1.540111] Freeing initrd memory: 18768K (ffff880004000000 - ffff880005254000) + ... + +Later it actually starts using it:: + + Begin: Running /scripts/local-premount ... done. + +You should also see your boot disk turn up:: + + [ 4.357243] scsi 1:0:0:0: Direct-Access ATA ADATA SP310 5.2 PQ: 0 ANSI: 5 + [ 4.366860] sd 1:0:0:0: [sda] 62533296 512-byte logical blocks: (32.0 GB/29.8 GiB) + [ 4.375677] sd 1:0:0:0: Attached scsi generic sg0 type 0 + [ 4.381859] sd 1:0:0:0: [sda] Write Protect is off + [ 4.387452] sd 1:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA + [ 4.399535] sda: sda1 sda2 sda3 + +Linux has found the three partitions (sda1-3). Mercifully it doesn't print out +the GUIDs. In step 1 above we could have used:: + + setenv bootargs root=/dev/sda2 ro + +instead of the GUID. However if you add another drive to your board the +numbering may change whereas the GUIDs will not. So if your boot partition +becomes sdb2, it will still boot. For embedded systems where you just want to +boot the first disk, you have that option. + +The last thing you will see on the console is mention of plymouth (which +displays the Ubuntu start-up screen) and a lot of 'Starting' messages:: + + * Starting Mount filesystems on boot [ OK ] + +After a pause you should see a login screen on your display and you are done. + +If you want to put this in a script you can use something like this:: + + setenv bootargs root=UUID=b2aaf743-0418-4d90-94cc-3e6108d7d968 ro + setenv boot zboot 03000000 0 04000000 ${filesize} + setenv bootcmd "ext2load scsi 0:2 03000000 /boot/vmlinuz-3.13.0-58-generic; ext2load scsi 0:2 04000000 /boot/initrd.img-3.13.0-58-generic; run boot" + saveenv + +The \ is to tell the shell not to evaluate ${filesize} as part of the setenv +command. + +You can also bake this behaviour into your build by hard-coding the +environment variables if you add this to minnowmax.h: + +.. code-block:: c + + #undef CONFIG_BOOTCOMMAND + #define CONFIG_BOOTCOMMAND \ + "ext2load scsi 0:2 03000000 /boot/vmlinuz-3.13.0-58-generic; " \ + "ext2load scsi 0:2 04000000 /boot/initrd.img-3.13.0-58-generic; " \ + "run boot" + + #undef CFG_EXTRA_ENV_SETTINGS + #define CFG_EXTRA_ENV_SETTINGS "boot=zboot 03000000 0 04000000 ${filesize}" + +and change CONFIG_BOOTARGS value in configs/minnowmax_defconfig to:: + + CONFIG_BOOTARGS="root=/dev/sda2 ro" + +.. _here: https://en.wikipedia.org/wiki/GUID_Partition_Table +.. _this: http://events.linuxfoundation.org/sites/events/files/slides/chromeos_and_diy... +.. _that: http://events.linuxfoundation.org/sites/events/files/slides/elce-2014.pdf diff --git a/doc/arch/x86/x86.rst b/doc/arch/x86/x86.rst index e75b5a73ffc0..c435225da4eb 100644 --- a/doc/arch/x86/x86.rst +++ b/doc/arch/x86/x86.rst @@ -97,272 +97,9 @@ mtrr
Booting Ubuntu -------------- -As an example of how to set up your boot flow with U-Boot, here are -instructions for starting Ubuntu from U-Boot. These instructions have been -tested on Minnowboard MAX with a SATA drive but are equally applicable on -other platforms and other media. There are really only four steps and it's a -very simple script, but a more detailed explanation is provided here for -completeness. - -Note: It is possible to set up U-Boot to boot automatically using syslinux. -It could also use the grub.cfg file (/efi/ubuntu/grub.cfg) to obtain the -GUID. If you figure these out, please post patches to this README. - -Firstly, you will need Ubuntu installed on an available disk. It should be -possible to make U-Boot start a USB start-up disk but for now let's assume -that you used another boot loader to install Ubuntu. - -Use the U-Boot command line to find the UUID of the partition you want to -boot. For example our disk is SCSI device 0:: - - => part list scsi 0 - - Partition Map for SCSI device 0 -- Partition Type: EFI - - Part Start LBA End LBA Name - Attributes - Type GUID - Partition GUID - 1 0x00000800 0x001007ff "" - attrs: 0x0000000000000000 - type: c12a7328-f81f-11d2-ba4b-00a0c93ec93b - guid: 9d02e8e4-4d59-408f-a9b0-fd497bc9291c - 2 0x00100800 0x037d8fff "" - attrs: 0x0000000000000000 - type: 0fc63daf-8483-4772-8e79-3d69d8477de4 - guid: 965c59ee-1822-4326-90d2-b02446050059 - 3 0x037d9000 0x03ba27ff "" - attrs: 0x0000000000000000 - type: 0657fd6d-a4ab-43c4-84e5-0933c84b4f4f - guid: 2c4282bd-1e82-4bcf-a5ff-51dedbf39f17 - => - -This shows that your SCSI disk has three partitions. The really long hex -strings are called Globally Unique Identifiers (GUIDs). You can look up the -'type' ones `here`_. On this disk the first partition is for EFI and is in -VFAT format (DOS/Windows):: - - => fatls scsi 0:1 - efi/ - - 0 file(s), 1 dir(s) - - -Partition 2 is 'Linux filesystem data' so that will be our root disk. It is -in ext2 format:: - - => ext2ls scsi 0:2 - <DIR> 4096 . - <DIR> 4096 .. - <DIR> 16384 lost+found - <DIR> 4096 boot - <DIR> 12288 etc - <DIR> 4096 media - <DIR> 4096 bin - <DIR> 4096 dev - <DIR> 4096 home - <DIR> 4096 lib - <DIR> 4096 lib64 - <DIR> 4096 mnt - <DIR> 4096 opt - <DIR> 4096 proc - <DIR> 4096 root - <DIR> 4096 run - <DIR> 12288 sbin - <DIR> 4096 srv - <DIR> 4096 sys - <DIR> 4096 tmp - <DIR> 4096 usr - <DIR> 4096 var - <SYM> 33 initrd.img - <SYM> 30 vmlinuz - <DIR> 4096 cdrom - <SYM> 33 initrd.img.old - => - -and if you look in the /boot directory you will see the kernel:: - - => ext2ls scsi 0:2 /boot - <DIR> 4096 . - <DIR> 4096 .. - <DIR> 4096 efi - <DIR> 4096 grub - 3381262 System.map-3.13.0-32-generic - 1162712 abi-3.13.0-32-generic - 165611 config-3.13.0-32-generic - 176500 memtest86+.bin - 178176 memtest86+.elf - 178680 memtest86+_multiboot.bin - 5798112 vmlinuz-3.13.0-32-generic - 165762 config-3.13.0-58-generic - 1165129 abi-3.13.0-58-generic - 5823136 vmlinuz-3.13.0-58-generic - 19215259 initrd.img-3.13.0-58-generic - 3391763 System.map-3.13.0-58-generic - 5825048 vmlinuz-3.13.0-58-generic.efi.signed - 28304443 initrd.img-3.13.0-32-generic - => - -The 'vmlinuz' files contain a packaged Linux kernel. The format is a kind of -self-extracting compressed file mixed with some 'setup' configuration data. -Despite its size (uncompressed it is >10MB) this only includes a basic set of -device drivers, enough to boot on most hardware types. - -The 'initrd' files contain a RAM disk. This is something that can be loaded -into RAM and will appear to Linux like a disk. Ubuntu uses this to hold lots -of drivers for whatever hardware you might have. It is loaded before the -real root disk is accessed. - -The numbers after the end of each file are the version. Here it is Linux -version 3.13. You can find the source code for this in the Linux tree with -the tag v3.13. The '.0' allows for additional Linux releases to fix problems, -but normally this is not needed. The '-58' is used by Ubuntu. Each time they -release a new kernel they increment this number. New Ubuntu versions might -include kernel patches to fix reported bugs. Stable kernels can exist for -some years so this number can get quite high. - -The '.efi.signed' kernel is signed for EFI's secure boot. U-Boot has its own -secure boot mechanism - see `this`_ & `that`_. It cannot read .efi files -at present. - -To boot Ubuntu from U-Boot the steps are as follows: - -1. Set up the boot arguments. Use the GUID for the partition you want to boot:: - - => setenv bootargs root=/dev/disk/by-partuuid/965c59ee-1822-4326-90d2-b02446050059 ro - -Here root= tells Linux the location of its root disk. The disk is specified -by its GUID, using '/dev/disk/by-partuuid/', a Linux path to a 'directory' -containing all the GUIDs Linux has found. When it starts up, there will be a -file in that directory with this name in it. It is also possible to use a -device name here, see later. - -2. Load the kernel. Since it is an ext2/4 filesystem we can do:: - - => ext2load scsi 0:2 03000000 /boot/vmlinuz-3.13.0-58-generic - -The address 30000000 is arbitrary, but there seem to be problems with using -small addresses (sometimes Linux cannot find the ramdisk). This is 48MB into -the start of RAM (which is at 0 on x86). - -3. Load the ramdisk (to 64MB):: - - => ext2load scsi 0:2 04000000 /boot/initrd.img-3.13.0-58-generic - -4. Start up the kernel. We need to know the size of the ramdisk, but can use - a variable for that. U-Boot sets 'filesize' to the size of the last file it - loaded:: - - => zboot 03000000 0 04000000 ${filesize} - -Type 'help zboot' if you want to see what the arguments are. U-Boot on x86 is -quite verbose when it boots a kernel. You should see these messages from -U-Boot:: - - Valid Boot Flag - Setup Size = 0x00004400 - Magic signature found - Using boot protocol version 2.0c - Linux kernel version 3.13.0-58-generic (buildd@allspice) #97-Ubuntu SMP Wed Jul 8 02:56:15 UTC 2015 - Building boot_params at 0x00090000 - Loading bzImage at address 100000 (5805728 bytes) - Magic signature found - Initial RAM disk at linear address 0x04000000, size 19215259 bytes - Kernel command line: "root=/dev/disk/by-partuuid/965c59ee-1822-4326-90d2-b02446050059 ro" - - Starting kernel ... - -U-Boot prints out some bootstage timing. This is more useful if you put the -above commands into a script since then it will be faster:: - - Timer summary in microseconds: - Mark Elapsed Stage - 0 0 reset - 241,535 241,535 board_init_r - 2,421,611 2,180,076 id=64 - 2,421,790 179 id=65 - 2,428,215 6,425 main_loop - 48,860,584 46,432,369 start_kernel - - Accumulated time: - 240,329 ahci - 1,422,704 vesa display - -Now the kernel actually starts (if you want to examine kernel boot up message on -the serial console, append "console=ttyS0,115200" to the kernel command line):: - - [ 0.000000] Initializing cgroup subsys cpuset - [ 0.000000] Initializing cgroup subsys cpu - [ 0.000000] Initializing cgroup subsys cpuacct - [ 0.000000] Linux version 3.13.0-58-generic (buildd@allspice) (gcc version 4.8.2 (Ubuntu 4.8.2-19ubuntu1) ) #97-Ubuntu SMP Wed Jul 8 02:56:15 UTC 2015 (Ubuntu 3.13.0-58.97-generic 3.13.11-ckt22) - [ 0.000000] Command line: root=/dev/disk/by-partuuid/965c59ee-1822-4326-90d2-b02446050059 ro console=ttyS0,115200 - -It continues for a long time. Along the way you will see it pick up your -ramdisk:: - - [ 0.000000] RAMDISK: [mem 0x04000000-0x05253fff] - ... - [ 0.788540] Trying to unpack rootfs image as initramfs... - [ 1.540111] Freeing initrd memory: 18768K (ffff880004000000 - ffff880005254000) - ... - -Later it actually starts using it:: - - Begin: Running /scripts/local-premount ... done. - -You should also see your boot disk turn up:: - - [ 4.357243] scsi 1:0:0:0: Direct-Access ATA ADATA SP310 5.2 PQ: 0 ANSI: 5 - [ 4.366860] sd 1:0:0:0: [sda] 62533296 512-byte logical blocks: (32.0 GB/29.8 GiB) - [ 4.375677] sd 1:0:0:0: Attached scsi generic sg0 type 0 - [ 4.381859] sd 1:0:0:0: [sda] Write Protect is off - [ 4.387452] sd 1:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA - [ 4.399535] sda: sda1 sda2 sda3 - -Linux has found the three partitions (sda1-3). Mercifully it doesn't print out -the GUIDs. In step 1 above we could have used:: - - setenv bootargs root=/dev/sda2 ro - -instead of the GUID. However if you add another drive to your board the -numbering may change whereas the GUIDs will not. So if your boot partition -becomes sdb2, it will still boot. For embedded systems where you just want to -boot the first disk, you have that option. - -The last thing you will see on the console is mention of plymouth (which -displays the Ubuntu start-up screen) and a lot of 'Starting' messages:: - - * Starting Mount filesystems on boot [ OK ] - -After a pause you should see a login screen on your display and you are done. - -If you want to put this in a script you can use something like this:: - - setenv bootargs root=UUID=b2aaf743-0418-4d90-94cc-3e6108d7d968 ro - setenv boot zboot 03000000 0 04000000 ${filesize} - setenv bootcmd "ext2load scsi 0:2 03000000 /boot/vmlinuz-3.13.0-58-generic; ext2load scsi 0:2 04000000 /boot/initrd.img-3.13.0-58-generic; run boot" - saveenv - -The \ is to tell the shell not to evaluate ${filesize} as part of the setenv -command. - -You can also bake this behaviour into your build by hard-coding the -environment variables if you add this to minnowmax.h: - -.. code-block:: c - - #undef CONFIG_BOOTCOMMAND - #define CONFIG_BOOTCOMMAND \ - "ext2load scsi 0:2 03000000 /boot/vmlinuz-3.13.0-58-generic; " \ - "ext2load scsi 0:2 04000000 /boot/initrd.img-3.13.0-58-generic; " \ - "run boot" - - #undef CFG_EXTRA_ENV_SETTINGS - #define CFG_EXTRA_ENV_SETTINGS "boot=zboot 03000000 0 04000000 ${filesize}" - -and change CONFIG_BOOTARGS value in configs/minnowmax_defconfig to:: - - CONFIG_BOOTARGS="root=/dev/sda2 ro" +Typically U-Boot boots distributions automatically so long an `CONFIG_BOOTSTD`, +`CONFIG_BOOTSTD_DEFAULTS` and `CONFIG_EFI_LOADER` are enabled. See +:doc:`manual_boot` for how to do this manually.
Test with SeaBIOS ----------------- @@ -747,8 +484,5 @@ TODO List .. _microcode: http://en.wikipedia.org/wiki/Microcode .. _SFI: http://simplefirmware.org .. _MP: http://www.intel.com/design/archives/processors/pro/docs/242016.htm -.. _here: https://en.wikipedia.org/wiki/GUID_Partition_Table -.. _this: http://events.linuxfoundation.org/sites/events/files/slides/chromeos_and_diy... -.. _that: http://events.linuxfoundation.org/sites/events/files/slides/elce-2014.pdf .. _SeaBIOS: http://www.seabios.org/SeaBIOS .. _ACPI: http://www.acpi.info