Annotation of wikisrc/ports/evbarm/raspberry_pi.mdwn, revision 1.128

1.1       jakllsch    1: [[!meta title="NetBSD/evbarm on Raspberry Pi"]]
                      2: 
1.127     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 still 32-bit (aarch32) centric, even though as of mid 2020 aarch64 is also a normal approach.
1.39      wiki        4: 
1.127     gdt         5: Initial, limited, Raspberry Pi support was introduced in NetBSD 6.0.  NetBSD 7.0 added 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.  NetBSD 9 supports aarch64, meaning using the newer processors in 64-bit mode (via -current in mid 2018).
1.39      wiki        6: 
1.127     gdt         7: Overall, this page takes the view that NetBSD 7 and earlier are obsolete; aside from history, it is written as if those versions don't exist.
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)
1.126     gdt        41:  - RPI3 new SD host controller driver
1.123     gdt        42: 
1.125     gdt        43: ## NetBSD current
1.53      gdt        44: 
1.101     gdt        45:  - RPI3 builtin bluetooth
1.53      gdt        46: 
1.125     gdt        47: ## (maybe) NetBSD current, with manual steps
                     48: 
                     49:    These items do not work in the sense that they simply function after a standard install.  Being listed here implies only that there has been list traffic that implies that after taking a bunch of steps (e.g. new firmware, new dtbs, enabling drivers, applying patches), one can end up with the feature working.  The HOWTO explicitly refrains from describing these steps because they are ephemeral.  However, the fact that list traffic indicates success is possible is a clue that proper support is on the horizon, and that is notable.
                     50: 
1.127     gdt        51:  - RPI3 and RPI0W builtin WiFi
1.125     gdt        52: 
1.102     gdt        53: ## What needs documenting if it works
                     54: 
                     55:  - CM1
                     56:  - CM3
                     57:  - CM3lite
                     58: 
1.54      gdt        59: ## What needs work
1.53      gdt        60: 
1.122     gdt        61:  - RPI4 (as of 2020-01, still does not work in current)
1.53      gdt        62:  - USB (host); isochronous transfers.
1.105     gdt        63:  - RPI0W Bluetooth Low Energy (probably)
1.53      gdt        64: 
1.57      gdt        65: # CPU types
                     66: 
1.101     gdt        67:  - RPI1 uses "earmv6hf".
1.109     gdt        68:  - RPI0 uses "earmv6hf".
                     69:  - RPI0W uses "earmv6hf".
1.101     gdt        70:  - RPI2 uses "earmv7hf".
1.113     gdt        71:  - RPI2-1.2 uses "earmv7hf" or "aarch64" (armv8 CPU hardware)
                     72:  - RPI3 uses "earmv7hf" or "aarch64" (armv8 CPU hardware)
1.127     gdt        73:  - RPI4 \todo
1.57      gdt        74: 
1.101     gdt        75: 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        76: 
1.127     gdt        77: In theory the code compiled for earmv7hf will be faster, but anecdotal experience is that it doesn't matter that much.  \todo Post a link to a quality benchmark.
1.97      gdt        78: 
1.101     gdt        79: 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        80: 
1.113     gdt        81: The RPI2-1.2 and RPI3 have an armv8 CPU that supports aarch64 (64-bit
                     82: mode) in addition to aarch32 (regular 32-bit ARM).  This is supported,
1.127     gdt        83: from 9 onwards, by the "aarch64" MACHINE_ARCH of evbarm, also
1.123     gdt        84: available in build.sh via the alias evbarm64.  This is also
1.113     gdt        85: referred to as [[NetBSD/aarch64|aarch64]].
1.70      gdt        86: 
1.7       wiki       87: # Installation
1.53      gdt        88: 
1.62      gdt        89: ## SD card structure
                     90: 
1.86      gdt        91: 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.
                     92: 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        93: 
1.86      gdt        94: 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        95: 
1.91      gdt        96: 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.
                     97: 
1.62      gdt        98: ## Choosing a version
                     99: 
1.127     gdt       100: First, decide if you want to install a formal release (8.0 or 9.0), a stable branch build (netbsd-8, netbsd-9), or NetBSD-current.  For people who don't know how to choose among those, a recent build of netbsd-9 is probably best, with 9.0 the choice for those who value being at exactly a formal release.
1.65      gdt       101: 
                    102: See also "ebijun's image", below, which is NetBSD-current and includes packages.
1.58      gdt       103: 
                    104: ## Getting bits to install
                    105: 
1.96      gdt       106: 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       107: 
                    108: ### Building yourself
                    109: 
1.95      gdt       110: 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       111: 
1.59      gdt       112:  - ./build.sh -m evbarm -a earmv6hf -u release
                    113:  - ./build.sh -m evbarm -a earmv7hf -u release
1.95      gdt       114:  - ./build.sh -m evbearmv7hf-el -u release
1.81      gdt       115: 
1.94      gdt       116: 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       117: 
1.85      gdt       118: ### NetBSD autobuild HTTPS/FTP servers
1.58      gdt       119: 
1.115     sevan     120: 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       121: 
1.115     sevan     122: 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       123: 
                    124: ### release layout
                    125: 
1.96      gdt       126: Once you get to the releasedir, self-built and autobuild releases have the same structure.
                    127: 
1.85      gdt       128:  - The 'evbarm-earmv6hf/binary/gzimg/' directory contains an rpi.img file that will run on any of the RPI boards.
1.103     gdt       129:  - 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       130: 
1.95      gdt       131: \todo Explain why there is no armv7_inst.gz.
1.58      gdt       132: 
1.65      gdt       133: ## Preparing a uSD card
1.10      wiki      134: 
1.107     gdt       135: 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      136: 
1.60      gdt       137:  - gunzip rpi.img.gz
1.67      ryoon     138:  - dd if=rpi.img of=/dev/disk1
1.14      wiki      139: 
1.89      gdt       140: ## Console approaches
                    141: 
                    142: The standard approach is to use a USB keyboard and an HDMI monitor for installation.
                    143: 
1.58      gdt       144: ### Serial Console
                    145: 
1.89      gdt       146: 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      147: 
1.127     gdt       148:  - 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".   The serial port is at 115200 baud.
1.41      wiki      149: 
1.127     gdt       150:    - In Kermit, the commands are "set flow none", "set carrier-watch off", "set baud 115200", and, often on NetBSD, "set line /dev/dtyU0".
1.89      gdt       151:    - In minicom, run "minicom -s" and set hardware flow control to "no".
1.41      wiki      152: 
1.89      gdt       153: ### Enabling ssh for installation without any console
1.41      wiki      154: 
1.89      gdt       155: 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       156: 
1.89      gdt       157: ### Installation with sshramdisk image
1.65      gdt       158: 
1.89      gdt       159: 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       160: 
1.89      gdt       161:  - Connect an Ethernet cable from the RPI to a LAN with a DHCP server, and another host you can use for ssh.
                    162:  - Power on the RPI, and wait.  Watch the logs on the DHCP server, and find the IP address assigned to the RPI.
                    163:  - Use ssh to login to the address you found with user "sysinst", and password "netbsd".
                    164:  - When installing, ensure that you enable DHCP and ssh, so that you can log in again after the system is installed.
1.53      gdt       165: 
1.107     gdt       166: 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.
                    167: 
1.55      gdt       168: ## Installation via ebijun's image
                    169: 
1.58      gdt       170: As an alternative to the standard installation images, Jun Ebihara
                    171: provides an install image for Raspberry Pi that includes packages.  It
                    172: is based on NetBSD-current and is built for earmv6hf, and thus will
                    173: work on Raspberry Pi 1, 2 and 3.  This image is typically updated
                    174: every few weeks.
1.55      gdt       175: 
1.121     cnst      176:  - <https://github.com/ebijun/NetBSD/blob/master/RPI/RPIimage/Image/README>
1.55      gdt       177: 
1.98      gdt       178: ## Configuring 802.11
                    179: 
                    180: 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.
                    181: 
                    182: 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:
                    183: 
                    184:  - urtwn0: Realtek (0xbda) 802.11n WLAN Adapter (0x8176), rev 2.00/2.00, addr 5, MAC/BB RTL8188CUS, RF 6052 1T1R
                    185: 
1.90      gdt       186: ## Links
                    187: 
                    188: The following pages have been published by NetBSD community members.  (Note that some of them are old.)
                    189: 
                    190:  - https://www.cambus.net/netbsd-on-the-raspberry-pi/
                    191: 
1.74      gdt       192: # Maintaining a system
                    193: 
1.127     gdt       194: ## Booting single user
                    195: 
                    196: \todo Describe how to boot single user via the serial console and via the fb console.
                    197: 
1.78      gdt       198: ## vcgencmd
                    199: 
1.80      gdt       200: The program vcgencmd, referenced in the boot section,  can be found in pkgsrc/misc/raspberrypi-userland.
1.78      gdt       201: 
1.53      gdt       202: ## Updating the kernel
1.46      schmonz   203: 
1.42      wiki      204:  - Build a new kernel, e.g. using build.sh. It will tell you where the ELF version of the kernel is, e.g.
                    205: 
                    206:          ...
                    207:          Kernels built from RPI2:
                    208:           /Users/feyrer/work/NetBSD/cvs/src-current/obj.evbarm-Darwin-XXX/sys/arch/evbarm/compile/RPI2/netbsd
                    209:          ...
                    210: 
1.69      rin       211:  - 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     212:  - 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      213:  - reboot
                    214: 
1.127     gdt       215: \todo Explain if updating firmware is necessary when e.g. moving from 8 to 9, or 9 to current.
                    216: 
1.73      gdt       217: ## Updating the firmware
                    218: 
                    219: 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.
                    220: 
1.127     gdt       221: \todo Explain where the firmware is in the source tree, and note that it is not 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.
1.101     gdt       222: 
1.99      gdt       223: \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.
                    224: 
1.75      gdt       225: ## Booting
                    226: 
1.79      gdt       227: 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       228: 
1.112     gdt       229: 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       230: 
1.112     gdt       231: 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       232: 
1.77      gdt       233: 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       234: 
1.80      gdt       235: 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.
                    236: \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       237: 
1.101     gdt       238: 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       239: 
1.113     gdt       240: ## Split-mode aarch32/aarch64
                    241: 
                    242: \todo Verify this, and add any necessary cautions about boot code.
                    243: 
                    244: The aarch64 kernel can run aarch32 binaries, so one can boot a aarch64 kernel on a system with aarch32 userland.
                    245: 
1.93      gdt       246: # X11 and GPU
                    247: 
1.27      wiki      248: ## Video playback
1.128   ! gdt       249: 
1.29      wiki      250: 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      251: 
                    252: ## OpenGL ES
1.128   ! gdt       253: 
1.27      wiki      254: 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.
                    255: 
1.28      wiki      256: ## Quake 3
1.128   ! gdt       257: 
1.27      wiki      258: 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:
                    259: 
                    260:  - pak0.pk3 from Quake 3 CD
1.31      snj       261:  - additional pak files from the [games/ioquake3-pk3](http://pkgsrc.se/games/ioquake3-pk3) package
1.27      wiki      262:  - read/write permissions on /dev/vchiq and /dev/wsmouse
                    263: 
1.31      snj       264: Place the pak0.pk3 file in the /usr/pkg/lib/ioquake3/baseq3 directory.
1.27      wiki      265: 
1.32      wiki      266: ## RetroArch / Libretro
1.128   ! gdt       267: 
1.32      wiki      268: 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:
                    269: 
                    270:  - Install [emulators/retroarch](http://pkgsrc.se/emulators/retroarch)
                    271:  - 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       272:  - Make sure your user has read and write permissions on `/dev/vchiq`.
                    273:  - 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.
                    274:  - Configure retroarch by editing $HOME/.config/retroarch/retroarch.cfg:
                    275:        video_driver = "gl"
                    276:        input_driver = "null"
                    277:        joypad_driver = "sdl2"
1.116     nia       278:        menu_driver = "rgui"
1.32      wiki      279: 
1.53      gdt       280: # Developer notes
1.50      gdt       281: 
1.53      gdt       282: These notes are for people working on improvements to RPI support in NetBSD.
1.50      gdt       283: 
1.72      gdt       284: ## Updating the firmware version in the NetBSD sources
1.50      gdt       285: 
1.72      gdt       286: (Note that trying new firmware may result in a non-bootable system, so
                    287: be prepared to recover the bootable media with another system.)
1.50      gdt       288: 
1.72      gdt       289: Upstream firmware releases are
                    290: [on GitHub](https://github.com/raspberrypi/firmware/releases).
                    291: Copy all files except `kernel*.img` into `/boot` and reboot.
                    292: 
                    293: New firmware should pass all of the following tests before being committed to NetBSD.
1.50      gdt       294: 
1.53      gdt       295: - Audio
                    296: - OMXPlayer (and [[!template id=man name="vchiq"]])
                    297: - Serial/framebuffer console
                    298: - CPU frequency scaling
1.50      gdt       299: 
1.92      gdt       300: Tests should be run on all of `rpi[0123]`.
1.94      gdt       301: 
                    302: ## Testing with anita and qemu
                    303: 
1.111     gdt       304: See the anita section in the evbarm page.
1.94      gdt       305: 
1.110     gdt       306: 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      307: 
1.128   ! gdt       308: # Misc notes
1.119     leot      309: 
                    310: Miscellaneous notes about Raspberry PI.
                    311: 
                    312: ## Power supply needed (or: why there is a little rainbow square in the top-right corner?)
1.128   ! gdt       313: 
1.119     leot      314: Raspberry Pi devices are powered by 5V micro USB and a 2.5A (2500mA)
1.124     gdt       315: power supply is recommended.  For more information please read:
1.119     leot      316: 
                    317:  <https://www.raspberrypi.org/documentation/faqs/#pi-power>
                    318: 
                    319: Power glitches can also manifest in other ways, e.g. with an USB
                    320: disk plugged:
                    321: 
                    322: [[!template id=programlisting text="""
                    323: sd0(umass0:0:0:0): generic HBA error
                    324: sd0: cache synchronization failed
                    325: """]]
                    326: 
1.124     gdt       327: Using a recommended power supply avoid such issues.
1.119     leot      328: 
                    329: ## Xenon death flash (Raspberry Pi 2 is camera-shy)
1.128   ! gdt       330: 
1.119     leot      331: When using laser pointers or xenon flashes in cameras (or other
                    332: flashes of high-intensity long-wave light) against a Raspberry Pi
                    333: 2 the Pi can power itself off.
                    334: For more information please read:
                    335: 
                    336:  <https://www.raspberrypi.org/blog/xenon-death-flash-a-free-physics-lesson/>

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