Annotation of wikisrc/ports/evbarm/raspberry_pi.mdwn, revision 1.124

1.1       jakllsch    1: [[!meta title="NetBSD/evbarm on Raspberry Pi"]]
                      2: 
1.120     gdt         3: This page describes the NetBSD/evbarm port on [Raspberry Pi](http://www.raspberrypi.org) hardware.  All [board variants](https://en.wikipedia.org/wiki/Raspberry_Pi#Specifications) earlier than the RPI4 are believed supported, and specific boards known to work are listed.  We use e.g. "RPI2" to refer to "Raspberry Pi 2" to save precious bytes on this page.  This web page is 32-bit (aarch32) centric, as that has been until mid-2018 the only approach.
1.39      wiki        4: 
1.104     gdt         5: Initial, limited, Raspberry Pi support was introduced in NetBSD 6.0.  NetBSD 7.0 adds complete support for the board, along with introducing support for the quad-core Raspberry Pi 2 board.  Raspberry Pi 3 support was added for NetBSD 8, and backported to NetBSD 7 in July of 2017.  (This page assumes those using NetBSD 7 are using 7.2 or later, but note that everyone uses 8 or -current.)
1.39      wiki        6: 
1.120     gdt         7: In mid-2018, -current gained support for 64-bit ARM (aarch64) support.  This will be in NetBSD 9.
1.114     gdt         8: 
1.3       wiki        9: [[images/raspberrypi.jpg]]
                     10: 
1.26      wiki       11: [[!toc levels=2]]
                     12: 
1.14      wiki       13: <small>([Raspberry Pi image](http://www.flickr.com/photos/42325803@N07/8118758647/) by Christopher Lee used under CC-By-2.0 license)</small>
1.3       wiki       14: 
1.54      gdt        15: # What works (and what doesn't yet)
1.53      gdt        16: 
1.123     gdt        17: "Works" is primarily relative to the earmv6hf-el and earmv7hf-el CPU targets (32-bit).
                     18: 
1.70      gdt        19: ## NetBSD 7 and NetBSD 8
1.53      gdt        20: 
1.102     gdt        21:  - RPI1, RPI2, RPI2-1.2, RPI3, RPI3+ (except RPI3 builtin WiFi and bluetooth)
                     22:  - RPI0 and RPI0W are expected to work (without WiFi, and one needs fdt files \todo where from?)
1.101     gdt        23:  - multiple processors on RPI2/RPI3
1.74      gdt        24:  - boots normally to multiuser, with FAT32 boot partition on uSD
                     25:  - root filesystem can be uSD or USB-attached mass storage
1.53      gdt        26:  - serial or graphics console (with EDID query / parsing)
1.74      gdt        27:  - X11 via HDMI
                     28:  - GPU (VCHIQ) - 3D and video decode. man page missing.
                     29:  - USB host controller - dwctwo(4) and most devices work
                     30:  - USB Ethernet - usmsc(4)
1.53      gdt        31:  - DMA controller driver and sdhc(4) support
1.74      gdt        32:  - RNG
1.53      gdt        33:  - Audio: works. man page missing.
1.74      gdt        34:  - GPIO
1.53      gdt        35:  - I²C: works, could use enhancements, man page
                     36:  - SPI: could use enhancements, man page
                     37: 
1.123     gdt        38: ## NetBSD 9
                     39: 
                     40:  - aarch64 support (RPI3, and should work on all supported systems with 64-bit CPUs)
                     41: 
1.122     gdt        42: ## NetBSD current (and probably 9)
1.53      gdt        43: 
1.101     gdt        44:  - RPI3 builtin bluetooth
                     45:  - RPI3 new SD host controller driver
1.53      gdt        46: 
1.102     gdt        47: ## What needs documenting if it works
                     48: 
                     49:  - CM1
                     50:  - CM3
                     51:  - CM3lite
                     52: 
1.54      gdt        53: ## What needs work
1.53      gdt        54: 
1.122     gdt        55:  - RPI4 (as of 2020-01, still does not work in current)
1.53      gdt        56:  - USB (host); isochronous transfers.
1.105     gdt        57:  - RPI3, RPI0W builtin WiFi
                     58:  - RPI0W Bluetooth Low Energy (probably)
1.53      gdt        59: 
1.57      gdt        60: # CPU types
                     61: 
1.101     gdt        62:  - RPI1 uses "earmv6hf".
1.109     gdt        63:  - RPI0 uses "earmv6hf".
                     64:  - RPI0W uses "earmv6hf".
1.101     gdt        65:  - RPI2 uses "earmv7hf".
1.113     gdt        66:  - RPI2-1.2 uses "earmv7hf" or "aarch64" (armv8 CPU hardware)
                     67:  - RPI3 uses "earmv7hf" or "aarch64" (armv8 CPU hardware)
1.57      gdt        68: 
1.101     gdt        69: Note that one can run a build of earmv6hf on the 2 and 3.  There will still be a kernel7, built to use the 2/3 hardware, but with the armv6 instruction set.
1.96      gdt        70: 
1.101     gdt        71: In theory the code compiled for earmv7hf will be faster, but anecdotal experience is that it doesn't matter that much.
1.97      gdt        72: 
1.101     gdt        73: While the evbarm port has "eb" variants (for big-endian mode), the RPI systems do not support eb and these variants will not work.  Systems built with older CPU architectures (earm, earmv4, earmv5) are not expected to work on RPI.
1.96      gdt        74: 
1.113     gdt        75: The RPI2-1.2 and RPI3 have an armv8 CPU that supports aarch64 (64-bit
                     76: mode) in addition to aarch32 (regular 32-bit ARM).  This is supported,
1.123     gdt        77: from -9 onwards, by the "aarch64" MACHINE_ARCH of evbarm, also
                     78: available in build.sh via the alias evbarm64.  This is also
1.113     gdt        79: referred to as [[NetBSD/aarch64|aarch64]].
1.70      gdt        80: 
1.7       wiki       81: # Installation
1.53      gdt        82: 
1.62      gdt        83: ## SD card structure
                     84: 
1.86      gdt        85: The Raspberry Pi looks for firmware and kernel.img on the first FAT32 MBR partition of the uSD card.  A separate kernel (kernel7.img) is used on RPI2 and RPI3.
                     86: The NetBSD kernel will then find NetBSD MBR partition and within that the root disklabel partition, and use that FFS partition as the root filesystem.
1.62      gdt        87: 
1.86      gdt        88: A 2 GB card is the smallest workable size, and the installation image will fit.  After the first boot, the system resizes the NetBSD root partition to fill the card.  Note that swap is after /boot and before /, and not contained in the NetBSD fdisk partition.  However, if you don't try to change the partition structure, this should not cause you any trouble.
1.63      gdt        89: 
1.91      gdt        90: Note that SD cards generally have limited write tolerance, so you may wish to disable atime updates via the noatime option, as is done by the default installation.
                     91: 
1.62      gdt        92: ## Choosing a version
                     93: 
1.95      gdt        94: First, decide if you want to install a formal release (7.2 or 8.0), a stable branch build (netbsd-7, netbsd-8), or NetBSD-current.  For people who don't know how to choose among those, a recent build of netbsd-8 is probably best, with 8.0 the choice for those who value being at exactly a formal release.
1.65      gdt        95: 
                     96: See also "ebijun's image", below, which is NetBSD-current and includes packages.
1.58      gdt        97: 
                     98: ## Getting bits to install
                     99: 
1.96      gdt       100: You can either build a release yourself with build.sh, or get a release from the NetBSD HTTPS/FTP servers.  The bits from both sources should match, except for things like  timestamps, or because the sources are from slightly different points along branches.
1.58      gdt       101: 
                    102: ### Building yourself
                    103: 
1.95      gdt       104: Getting sources and building a release with build.sh is not special for evbarm.  However, the evbarm port has a very large number of CPU types, compared to i386 and amd64 which have one each.  The standard approach is to use -m to define MACHINE and -a to define MACHINE_ARCH.  build.sh supports aliases that can be passed as a MACHINE value, but denote both MACHINE and a MACHINE_ARCH.   The third line uses an alias and is equal to the second, for RPI2/3.  Note that the aliases start with "evb" while the MACHINE_ARCH values do not, and that aliases have "-el" or "-eb", while the MACHINE_ARCH values have no suffix or "eb".
1.66      gdt       105: 
1.59      gdt       106:  - ./build.sh -m evbarm -a earmv6hf -u release
                    107:  - ./build.sh -m evbarm -a earmv7hf -u release
1.95      gdt       108:  - ./build.sh -m evbearmv7hf-el -u release
1.81      gdt       109: 
1.94      gdt       110: Consider setting RELEASEMACHINEDIR if you wish to build multiple MACHINE_ARCH values for a MACHINE; see build.sh.  Use something like "evbarm-earmv7hf", so that 1) earvm6 and earmv7 don't collide and 2) anita will recognize it as a type of evbarm.
1.58      gdt       111: 
1.85      gdt       112: ### NetBSD autobuild HTTPS/FTP servers
1.58      gdt       113: 
1.115     sevan     114: NetBSD provides nightly builds on [nycdn.netbsd.org](https://nycdn.netbsd.org/pub/NetBSD-daily/).  The next directory level is the branch being built (netbsd-7, netbsd-8, HEAD, and more), plus optionally things like compiler type.  It is followed by date/time, e.g. "HEAD/201811051650Z"; once a build is complete the symlink "latest" is adjusted to point to it.  The next level is "${MACHINE}-${MACHINE_ARCH}", e.g. "evbarm-earmv7hf", and multiple combinations are provided.
1.58      gdt       115: 
1.115     sevan     116: An example URL, arguably the standard approach for first-time NetBSD/RPI users, is https://nycdn.netbsd.org/pub/NetBSD-daily/netbsd-8/latest/evbarm-earmv7hf/binary/gzimg/
1.95      gdt       117: 
                    118: ### release layout
                    119: 
1.96      gdt       120: Once you get to the releasedir, self-built and autobuild releases have the same structure.
                    121: 
1.85      gdt       122:  - The 'evbarm-earmv6hf/binary/gzimg/' directory contains an rpi.img file that will run on any of the RPI boards.
1.103     gdt       123:  - The 'evbarm-earmv7hf/binary/gzimg/' directory contains an armv7.img file that uses the armv7 instruction set, and thus can run only on the RPI2 and RPI3 (and perhaps the CM3).  It also supports systems other than the RPI family.
1.85      gdt       124: 
1.95      gdt       125: \todo Explain why there is no armv7_inst.gz.
1.58      gdt       126: 
1.65      gdt       127: ## Preparing a uSD card
1.10      wiki      128: 
1.107     gdt       129: Once you have rpi.img.gz (or rpi_inst for earmv6 boards), put it on a uSD card using gunzip and dd, for example:
1.14      wiki      130: 
1.60      gdt       131:  - gunzip rpi.img.gz
1.67      ryoon     132:  - dd if=rpi.img of=/dev/disk1
1.14      wiki      133: 
1.89      gdt       134: ## Console approaches
                    135: 
                    136: The standard approach is to use a USB keyboard and an HDMI monitor for installation.
                    137: 
1.58      gdt       138: ### Serial Console
                    139: 
1.89      gdt       140: By default the rpi.img is set to use the HDMI output.  If you wish to use a serial console, mount the FAT32 partition on another system and edit cmdline.txt and remove '"console=fb"'.
1.14      wiki      141: 
1.109     gdt       142:  - Most (all?) USB-to-TTL serial adapters have wires for TX, RX and ground, and not RTS/CTS or other flow control lines.   Thus, your terminal program (or terminal) must be configured to not require flow control; a symptom of misconfiguration is that you see console output, but cannot type anything.  If so, adjust your serial console application's flow control settings to "none".
1.41      wiki      143: 
1.89      gdt       144:    - In Kermit, the command is "set flow none".
                    145:    - In minicom, run "minicom -s" and set hardware flow control to "no".
1.41      wiki      146: 
1.89      gdt       147: ### Enabling ssh for installation without any console
1.41      wiki      148: 
1.89      gdt       149: If you want to enable ssh with the standard image, so that you can log in over the net without either a serial or HDMI console, you can edit the configuration of a uSD card before booting.   On another computer, mount the ffs partition, place /root/.ssh/authorized_keys, uncomment PermitRootLogin in /etc/ssh/sshd_config, and comment out the rc_configure=NO in /etc/rc.conf.  Besides having to find the IP address (e.g. from DHCP server logs), you will have to wait for the partition resizing and reboot.
1.65      gdt       150: 
1.89      gdt       151: ### Installation with sshramdisk image
1.65      gdt       152: 
1.89      gdt       153: build.sh (and hence the FTP site) also creates an image 'rpi_inst.img.gz' specifically for installation without HDMI or a serial console, when built for earmv6hf.  Note that this image is much smaller and that you will need to fetch the sets over the network.  To use this method, write that image to a uSD card as above, and then:
1.58      gdt       154: 
1.89      gdt       155:  - Connect an Ethernet cable from the RPI to a LAN with a DHCP server, and another host you can use for ssh.
                    156:  - Power on the RPI, and wait.  Watch the logs on the DHCP server, and find the IP address assigned to the RPI.
                    157:  - Use ssh to login to the address you found with user "sysinst", and password "netbsd".
                    158:  - When installing, ensure that you enable DHCP and ssh, so that you can log in again after the system is installed.
1.53      gdt       159: 
1.107     gdt       160: The rpi_inst.img.gz image will only work for systems that use earmv6hf kernels (so not RPI2/3).  See [this port-arm message](https://mail-index.netbsd.org/port-arm/2017/08/18/msg004374.html) for details.
                    161: 
1.55      gdt       162: ## Installation via ebijun's image
                    163: 
1.58      gdt       164: As an alternative to the standard installation images, Jun Ebihara
                    165: provides an install image for Raspberry Pi that includes packages.  It
                    166: is based on NetBSD-current and is built for earmv6hf, and thus will
                    167: work on Raspberry Pi 1, 2 and 3.  This image is typically updated
                    168: every few weeks.
1.55      gdt       169: 
1.121     cnst      170:  - <https://github.com/ebijun/NetBSD/blob/master/RPI/RPIimage/Image/README>
1.55      gdt       171: 
1.98      gdt       172: ## Configuring 802.11
                    173: 
                    174: After installation, the Ethernet will function as on any other NetBSD system; simply enable dhcpcd or configure a static address.  USB WiFi devices will also function as on any other NetBSD system; in addition to dhcpcd or static, configure and enable wpa_supplicant.
                    175: 
                    176: Note that the built-in WiFi in the RPI3 is not yet supported.   USB WiFi interfaces (that work on NetBSD in general) should all work.  In particular, the following are known to work:
                    177: 
                    178:  - urtwn0: Realtek (0xbda) 802.11n WLAN Adapter (0x8176), rev 2.00/2.00, addr 5, MAC/BB RTL8188CUS, RF 6052 1T1R
                    179: 
1.90      gdt       180: ## Links
                    181: 
                    182: The following pages have been published by NetBSD community members.  (Note that some of them are old.)
                    183: 
                    184:  - https://www.cambus.net/netbsd-on-the-raspberry-pi/
                    185: 
1.74      gdt       186: # Maintaining a system
                    187: 
1.78      gdt       188: ## vcgencmd
                    189: 
1.80      gdt       190: The program vcgencmd, referenced in the boot section,  can be found in pkgsrc/misc/raspberrypi-userland.
1.78      gdt       191: 
1.53      gdt       192: ## Updating the kernel
1.46      schmonz   193: 
1.42      wiki      194:  - Build a new kernel, e.g. using build.sh. It will tell you where the ELF version of the kernel is, e.g.
                    195: 
                    196:          ...
                    197:          Kernels built from RPI2:
                    198:           /Users/feyrer/work/NetBSD/cvs/src-current/obj.evbarm-Darwin-XXX/sys/arch/evbarm/compile/RPI2/netbsd
                    199:          ...
                    200: 
1.69      rin       201:  - Besides the "netbsd" kernel in ELF format, there is also a "netbsd.img" (for current) or "netbsd.bin" (for 7 and 8) kernel that is in a format that the Raspberry can boot.
1.48      sevan     202:  - Depending on your hardware version, copy this either to /boot/kernel.img (First generation Pi, Pi Zero hardware) or to /boot/kernel7.img (Pi 2, Pi 3 hardware)
1.42      wiki      203:  - reboot
                    204: 
1.73      gdt       205: ## Updating the firmware
                    206: 
                    207: A section below describes the process of updating NetBSD's copy of the firmware from upstream, with testing, by NetBSD developers.  This section is about updating a system's firmware from the firmware in a version of NetBSD.
                    208: 
1.88      gdt       209: \todo Explain where the firmware is in the source tree, and if it is in the installed system image (such as /usr/mdec).  Explain how to update a system (presumably /boot) from either an installed system's new firmware files, or the source tree.  Explain any particular cautions.
1.73      gdt       210: 
1.105     gdt       211: Probably, for the RPI3+, one needs to use -current, or use -8 with firmware from -current.  \todo Defuzz.
1.101     gdt       212: 
1.99      gdt       213: \todo Explain if using updated firmware from one branch (e.g. netbsd-current) on a system using a different branch (e.g. netbsd-8) is safe.  Explain if pullups are done to release branches with new firmware.
                    214: 
1.75      gdt       215: ## Booting
                    216: 
1.79      gdt       217: The device boots by finding a file "bootcode.bin".   The primary location is a FAT32 partition on the uSD card, and an additional location is on a USB drive.  See the [upstream documentation on booting](https://www.raspberrypi.org/documentation/hardware/raspberrypi/bootmodes/) and read all the subpages.
1.75      gdt       218: 
1.112     gdt       219: The standard approach is to use a uSD card, with a fdisk partition table containing a FAT32 partition marked active, and a NetBSD partition.  The NetBSD partition will then contain a disklabel, pointing to an FFS partition (a), a swap partition (b) and the FAT32 boot partition mounted as /boot (e).  The file /boot/cmdline.txt has a line to set the root partition.
1.75      gdt       220: 
1.112     gdt       221: One wrinkle in the standard approach is that the disk layout is "boot swap /", but the NetBSD fdisk partition starts at the location of /, so the swap partition is not within the NetBSD fdisk partition.  The / partition can hold a disklabel, while swap cannot.   It is normal to have swap after / (and thus within the fdisk partition), but the arrangement used permits growing / on first boot, for the typical case where a larger uSD is used, compared to the minimum image size.
1.75      gdt       222: 
1.77      gdt       223: An alternate approach is to have the boot FAT32 partition as above, but to have the entire system including root on an external disk.  This is configured by changing root=ld0a to root=sd0a or root=dk0 (depending on disklabel/GPT).  Besides greater space, part of the point is to avoid writing to the uSD card.
1.75      gdt       224: 
1.80      gdt       225: A third approach, workable on the Pi 3 only, is to configure USB host booting (already enableed on the 3+; see the upstream documentation) and have the boot partition also on the external device.  In this case the external device must have an MBR because the hardware's first-stage boot does not have GPT support. In theory the [procedure to program USB host boot mode](https://www.raspberrypi.org/documentation/hardware/raspberrypi/bootmodes/msd.md) will function on a NetBSD system because the programming is done by bootcode.bin.
                    226: \todo Confirm that putting program_usb_boot_mode=1 in config.txt and booting works to program the OTP bit.  Confirm that one can then boot NetBSD from external USB.
1.75      gdt       227: 
1.101     gdt       228: There is no well-defined USB enumeration order, so the preferred approach if one has multiple USB mass storage devices is to use named wedges in both fstab and cmdline.txt.
1.75      gdt       229: 
1.113     gdt       230: ## Split-mode aarch32/aarch64
                    231: 
                    232: \todo Verify this, and add any necessary cautions about boot code.
                    233: 
                    234: The aarch64 kernel can run aarch32 binaries, so one can boot a aarch64 kernel on a system with aarch32 userland.
                    235: 
1.93      gdt       236: # X11 and GPU
                    237: 
1.27      wiki      238: ## Video playback
1.29      wiki      239: Accelerated video playback is supported in NetBSD 7 with the [OMXPlayer](http://pkgsrc.se/multimedia/omxplayer) application and through GStreamer with the [omx](http://pkgsrc.se/multimedia/gst-plugins1-omx) plugin.
1.27      wiki      240: 
                    241: ## OpenGL ES
                    242: Accelerated OpenGL ES is supported in NetBSD 7. The GL ES client libraries are included with the [misc/raspberrypi-userland](http://pkgsrc.se/misc/raspberrypi-userland) package.
                    243: 
1.28      wiki      244: ## Quake 3
1.27      wiki      245: A Raspberry Pi optimized build of *ioquake3* is available in the [games/ioquake3-raspberrypi](http://pkgsrc.se/games/ioquake3-raspberrypi) package. To use it, the following additional resources are required:
                    246: 
                    247:  - pak0.pk3 from Quake 3 CD
1.31      snj       248:  - additional pak files from the [games/ioquake3-pk3](http://pkgsrc.se/games/ioquake3-pk3) package
1.27      wiki      249:  - read/write permissions on /dev/vchiq and /dev/wsmouse
                    250: 
1.31      snj       251: Place the pak0.pk3 file in the /usr/pkg/lib/ioquake3/baseq3 directory.
1.27      wiki      252: 
1.32      wiki      253: ## RetroArch / Libretro
                    254: Using [emulators/retroarch](http://pkgsrc.se/emulators/retroarch) it is possible to run many emulators at full speed the Raspberry Pi. Emulator cores for various gaming consoles are available in the [emulators/libretro-*](http://pkgsrc.se/search.php?so=libretro-) packages. To begin using retroarch:
                    255: 
                    256:  - Install [emulators/retroarch](http://pkgsrc.se/emulators/retroarch)
                    257:  - Install the libretro core for the system you would like to emulate (lets take [emulators/libretro-gambatte](http://pkgsrc.se/emulators/libretro-gambatte), a GameBoy Color emulator, as an example).
1.118     nia       258:  - Make sure your user has read and write permissions on `/dev/vchiq`.
                    259:  - Plug in a USB HID compatible Gamepad, such as the Logitech F710 in "DirectInput" mode (set "D/X" switch to "D"). Note that since the framebuffer GL driver will not allow for keyboard input in RetroArch, you will have to copy your joypad configuration from another system.
                    260:  - Configure retroarch by editing $HOME/.config/retroarch/retroarch.cfg:
                    261:        video_driver = "gl"
                    262:        input_driver = "null"
                    263:        joypad_driver = "sdl2"
1.116     nia       264:        menu_driver = "rgui"
1.32      wiki      265: 
1.53      gdt       266: # Developer notes
1.50      gdt       267: 
1.53      gdt       268: These notes are for people working on improvements to RPI support in NetBSD.
1.50      gdt       269: 
1.72      gdt       270: ## Updating the firmware version in the NetBSD sources
1.50      gdt       271: 
1.72      gdt       272: (Note that trying new firmware may result in a non-bootable system, so
                    273: be prepared to recover the bootable media with another system.)
1.50      gdt       274: 
1.72      gdt       275: Upstream firmware releases are
                    276: [on GitHub](https://github.com/raspberrypi/firmware/releases).
                    277: Copy all files except `kernel*.img` into `/boot` and reboot.
                    278: 
                    279: New firmware should pass all of the following tests before being committed to NetBSD.
1.50      gdt       280: 
1.53      gdt       281: - Audio
                    282: - OMXPlayer (and [[!template id=man name="vchiq"]])
                    283: - Serial/framebuffer console
                    284: - CPU frequency scaling
1.50      gdt       285: 
1.92      gdt       286: Tests should be run on all of `rpi[0123]`.
1.94      gdt       287: 
                    288: ## Testing with anita and qemu
                    289: 
1.111     gdt       290: See the anita section in the evbarm page.
1.94      gdt       291: 
1.110     gdt       292: It is not currently known how to emulate a RPI in qemu, and therefore anita does not yet have support for this.  \todo Add a command-line example to run qemu emulating some RPI model.
1.119     leot      293: 
                    294: 
                    295: # Misc notes
                    296: Miscellaneous notes about Raspberry PI.
                    297: 
                    298: ## Power supply needed (or: why there is a little rainbow square in the top-right corner?)
                    299: Raspberry Pi devices are powered by 5V micro USB and a 2.5A (2500mA)
1.124   ! gdt       300: power supply is recommended.  For more information please read:
1.119     leot      301: 
                    302:  <https://www.raspberrypi.org/documentation/faqs/#pi-power>
                    303: 
                    304: Power glitches can also manifest in other ways, e.g. with an USB
                    305: disk plugged:
                    306: 
                    307: [[!template id=programlisting text="""
                    308: sd0(umass0:0:0:0): generic HBA error
                    309: sd0: cache synchronization failed
                    310: """]]
                    311: 
1.124   ! gdt       312: Using a recommended power supply avoid such issues.
1.119     leot      313: 
                    314: ## Xenon death flash (Raspberry Pi 2 is camera-shy)
                    315: When using laser pointers or xenon flashes in cameras (or other
                    316: flashes of high-intensity long-wave light) against a Raspberry Pi
                    317: 2 the Pi can power itself off.
                    318: For more information please read:
                    319: 
                    320:  <https://www.raspberrypi.org/blog/xenon-death-flash-a-free-physics-lesson/>

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