Electronics project notes/Microcontroller and computer platforms
Contents
- 1 Microcontrollers and their common platforms (or otherwise comparatively slow)
- 1.1 On speed
- 1.2 On RAM
- 1.3 AVR and Arduino
- 1.4 ARM Cortex(-M)
- 1.5 ESP8266, ESP32, etc.
- 2 Haven't personally used" list
- 3 Computer-like
- 4 NSLU, NSLU2
- 5 Router hacking (mostly for Linksys WRT54 and similar)
- 6 See also
Microcontrollers and their common platforms (or otherwise comparatively slow)
Some pointers for choosing:
- programmability ease - if it means an expensive programmer, hobbyists won't be so interested. If you can do it via an USB/serial cable, yay.
- memory size
- (...and limits imposed by architecture)
- 8KB isn't much if you want one complex library
- External RAM/ROM is possible, but often bothersome
- physical packaging - if it has a tiny-pitch SMT, you'll probably rely on buying pre-built boards, while 0.1" DIP is more flexible, and can be cheaper than said boards.
On speed
Tends to depend on what you want, but of the buyable-as-a-DIY-board
- Teensy 4 are faster than most of the below, but also pricier
- due to low price, ESP32's are some of the best speed per price
- though its FPU isn't as good as some (e.g. STM32F4)
- STM32F4 (black pills) coming in second
- and STM32F1's (blue pills) and ESP8266 coming in third
Arduino Due, and Teensy 3, are presumably comparable to blue pills (verify)
On RAM
AVR and Arduino
The Arduino is mostly based on (8-bit) Atmel AVR[1] microcontrollers. (With recent models this is shifting)
Probably the main reason for its initial popularity is the fairly low price combined with the ease of prototyping (both for standalone and for slave-to-a-PC projects).
Arduinos/AVRs technically always were slowish for their price, in that even a decade ago there were better speed-for-price choices, but most also require more investment of time and peripheral hardware.
In short, Arduino was great for hobby stuff. (PIC too, actually, it was just a different community)
You get
- programmability without a costly programmer
- (for most boards you only need a USB cable, and in some minimal boards you need a USB-to-serial device)
- an IDE were you don't have to dig deep to get started
- a bunch of IO pins that you can leverage using just a few bits of code (bunch of GPIO pins, a 10 bit ADC multiplexed to some of them, PWM on some of them),
The arduino board is a very convenient wrapper around the heart of the board that is the AVR (which by itself costs only ~EUR 5 or less, and you can build stripped-down versions yourself.
When you do want more speed, video (color composite video generation is about the limit, and you need an AVR pretty much dedicated to it), audio intput/output, USB, Ethernet at faster-than-serial-port speeds, or such you probably want boards with things like ARM processors and chips dedicated to such input and ouput. beagleboard and sheevaplug come to mind.
See Electronics project notes/Arduino notes for some more detailed notes.
ARM Cortex(-M)
For context
ARM is a company[2].
It is best known for its ARM architecture, mainly designs a specific RISC-style CPU architecture that lends itself to a wide range of embedded processing, SoCs, and even some more serious calculation.
In the embedded/DIY realm we are often specifically interested in ARM Cortex (and then often ARM Cortex-M) family, itself split into three series:
- Cortex-M made for low cost and low power
- which makes it interesting for 'microcontroller but faster' uses
- Cortex-A
- which is fast enough for a basic OS (e.g. used in Raspberry Pi)
Teensy
While Teensy 2 are AVRs (at 16MHz so comparable to Arduino Mini/Nano), Teensy 3 and 4 are ARM Cortex-M:
Teensy 3
- Teensy LC is an ARM Cortex-M0+ at 48MHz, ~EUR13
- Teensy 3.0 is an ARM Cortex M4 48MHz, ~EUR20
- Teensy 3.1 is an ARM Cortex M4 72MHz, ~EUR20
- Teensy 3.2 is an ARM Cortex-M4 at 72MHz, ~EUR20
- Teensy 3.5 is an ARM Cortex-M4F at 120MHz, ~EUR30
- Teensy 3.6 is an ARM Cortex-M4F at 180MHz, ~EUR35
Teensy 4
- Teensy 4.0 and 4.1 are an ARM Cortex-M7 at 600MHz
- 4.0 is more bare-bones (2 Mbyte flash, 1 Mbyte RAM), for EUR20
- 4.1 adds an Ethernet IC, SD card socket, 5-pin USB header. ~EUR26
RAM:
- 64KB for 3.2
- 256KB for 3.5 and 3.6
- 1024KB for 4.0, 4.1
- note: 4.1 also has pads for PSRAM and/or more flash
Current:
- Teensy 3 up to ~40mA?(verify)
- Teensy 4 ~100mA at 600MHz
Teensy 3 and 4 are 3.3v devices and not 5V tolerant.
See
Note that the 3+ are 3.3V devices (only some 5V tolerant)
Teensy 4 memory
The 1024 KByte is split into
- RAM1
- 512KB
- more tightly coupled. Code, static variables, and stack will be put here
- RAM2
- 512KB
- runs slower
- used for buffers, larger arrays, and dynamic allocations
Atmel SAM (Arduino Zero, Due; Seeed XIAO)
ARM Cortex-M
https://en.wikipedia.org/wiki/Atmel_ARM-based_processors
Boards interesting to DIYers include:
- Arduino Zero uses ATSAMD21G18, which is Cortex-M0+
- Arduino Due uses AT91SAM3X8E, which is Cortex-M3
STM32
STM32 are a licensed[3] bunch of series of Cortex-M based devices.
Many individual models over various series, but (currently) broadly with speeds somewhere between 20 and 200MHz, and with SRAM and flash up to a few hundred KB.
A subset of pins are 5V tolerant (when you disable pullup/pulldown), others are not,
so you should probably consider this a 3.3V device (sometimes run down to 2V)
A bunch of pre-made boards may be interesting to DIYers, including
Voltage and current
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
Regularly run at 3.3V (down to 2V), generally considered a 3.3V device.
A subset of pins are 5V tolerant (when you disable pullup/pulldown), others are not.
As to power draw, maybe run STM32CubeMX - it's meant to enable/disable specific peripherals, and configure CPU idle rates, and estimate the resulting current.
Models and boards
Starting to understand model codes
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
1 letter: Type/market
- F - Foundation / general purpose (probably the most common?)
- L - Low-power
- G - Mainstream
- H - High performance
- W - Wireless
1 digit: Core
- 0 - Cortex M0
- 1 - Cortex M3
- 2 - Cortex M3
- 3 - Cortex M4
- 4 - Cortex M4
- 7 - Cortex M7
(These two combine as a series. Not all exist, see series list below)
2 digits: Product line within the series - so the meaning varies per series
- e.g. for F1
- 00 - 24MHz, motor control
- 01 - 36MHz
- 02 - 48MHz, USB
- 03 - 72MHz, USB, CAN, motor control
- 05, 07 - 72MHz, Ethernet, CAN, USB OTG
- e.g. for F4 (most have USB, many have crypto and rng) (verify) TODO: finish this list
- 01 - 84MHz
- 05/15 - 168MHz, 2 DACs,
- 07/17 - 168MHz, 2 DACs, Ethernet, camera interface
- 10 - 100MHz, DAC
- 11 - 100MHz, 5 SPI
- 12 - 100MHz,
- 13/23 - 100MHz, more serial ports than most
- 27/37 - 180MHz, memory controller
- 29/39 - 180MHz, memory controller
- 46 - 180MHz, memory controller
- 69/79 - 180MHz, LCD-TFT and MPI-DSI
1 letter: pin count (will roughly correlate with package type), e.g.
- C - 48 (or 49)
- R - 64 (or 66)
- V - 100
- O - 90
- Z - 144
- (the list is longer, omitted for brevity)
1 letter/number: Flash size (within a line this is strongly correlated to RAM(verify)), e.g.
- 4 - 16KiB Flash (RAM e.g. 6KiB for F1)
- 6 - 32KiB Flash (RAM e.g. 10KiB for F1)
- 8 - 64KiB Flash (RAM e.g. 20KiB for F1)
- B - 128KiB Flash (RAM e.g. 20KiB for F1, 64KiB for F4)
- C - 256KiB Flash (RAM e.g. 48KiB for F1, 64KiB for F4)
- D - 384KiB Flash (RAM e.g. 96KiB for F4)
- E - 512KiB Flash (RAM e.g. 96KiB for F4)
- F - 768KiB Flash
- G - 1024KiB Flash (RAM e.g. 96KiB for F4)
- H - 1536KiB Flash
- I - 2048KiB Flash
- (the list is longer, omitted for brevity)
1 letter: Package, e.g.
- T - LQFP
- (the list is longer, omitted for brevity)
1 number: Temperature
- 6 - -40C to 85C
- 7 - -40C to 105C
See also:
- https://www.digikey.com/en/maker/blogs/2020/understanding-stm32-naming-conventions
- https://www.st.com/en/microcontrollers-microprocessors/stm32-32-bit-arm-cortex-mcus.html
It seems the series that exist are currently:
- F1 series (launched 2007), Cortex-M3
- F2 series (launched 2010), Cortex-M3
- L1 series (launched 2010), Cortex-M3
- F4 series (launched 2011), Cortex-M4F
- F3 series (launched 2012), Cortex-M4F
- F0 series (launched 2012), Cortex-M0
- F7 series (launched 2014), Cortex-M7F (pin compatible with F4, faster)
- L0 series (launched 2014), Cortex-M0+
- L4 series (launched 2015), Cortex-M4F
- L4+ series (launched 2016)
- H7 series (launched 2017), Cortex-M7F
- L5 series (launched 2018), Cortex-M33F
- G0 series (launched 2018), lower-power variants of L0 (Cortex-M0+)
Also:
For example:
- STM32F103C8T6
- STM32F103RBT6
- STM32F103RCT6
- STM32F405RGT6
- STM32F407VGT6
- STM32F401CEU6
- STM32F411CEU6
The first three are F1 series and all F103 line.
The last four are F4 series, and four different lines (F405, F407, F401, F411).
IO featureset will vary between distinct lines,
but also note that fewer-pin versions within a line can omit things because they don't have enough pins to expose them, so consult the datasheet.
Datasheets will often be for a line, part of a line , or group a few similar-enough lines basically varying with how similar their features are.
Blue pill notes
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
Blue Pill boards are typically based on the STM32F103C8T6 (a Cortex-M3, STM32F1 series - 72MHz, 64KiB Flash, 20KiB SRAM.
If USB doesn't work:
- R10 problem: R10 on the board is the USB's D+ line pullup, which should be 1.5k -- but is higher on many older blue pill boards
- there's a hack in putting something in parallel on external pins (e.g. if the resistor is 10k, adding ~1.8k should work)
- Many boards do not come with a USB-capable firmware/bootloader(verify)
- you will need to flash one over serial
- Note that USB code takes ~20KB, so if you don't need it, you may want to skip that
- (that said, most people don't need a huge amount of code, so USB is just nice to have)
BOOT0 BOOT1 0 x on-board flash (the firmware you wrote) 1 0 system ROM (mostly for programming mode, see ST AN2606) 1 1 SRAM (certain debugging, sometimes being controlled by something else)
...so most of us only care to set BOOT0, to switch between low=flashing and high=operating (on many versions that't the top jumper left and right, respectively)
Black pill (Blue Pill 2) notes
Black Pill boards are typically based on the STM32F401CCU6 or STM32F411CEU6 (Cortex-M4F, STM32F4 series)
Compared to blue pill, these will have
- FPU
- higher clock speed (84 and 100MHz)
- 256 or 512KB flash
- 64 or 128KB SRAM
- USB-C port
- a few more IO options (but how much is exposed)
They cost maybe twice as much, which is still not much
Nucleo
https://www.st.com/en/evaluation-tools/stm32-nucleo-boards.html
Maple
https://www.leaflabs.com/maple/
Hardware
IO
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
Serial ports
Some series have up to 5 hardware serial ports, but most DIY boards have only three.
Note they share pins with other functions (like ADC, PWM, I2C)
The USB can be used to talk serial, but details vary a little with the firmware being used.
CDC
https://github.com/stm32duino/wiki/wiki/API#hardwareserial
https://www.stm32duino.com/viewtopic.php?t=291
https://www.stm32duino.com/viewtopic.php?t=269
In Arduino:
5V tolerance
A number of pins seem to have what amounts to level shifters, so can talk 5V (when powered by 5V?).
You may be best off looking at a pinout.
Though note:
- this doesn't apply when using pullup (/pulldown(verify)) because it's to a different voltage(verify)
- that circuit it doesn't work when powered off(verify)
For voltage levels, see 6.3.14, but basically, they are compliant to both CMOS and TTL levels (and the precise voltage behaviour differs slightly between regular and 5V tolerant pins).
http://www.emcu.eu/000/STM32_5VtolerantIO.pdf
ADC and DAC notes
Many have (12-bit(verify)) ADCs (some multiple)
Some have (12-bit) DACs (max speed in the megasample range, varying with series)
Sound output
Choose between the DAC and I2S
- internal DAC is cheaper, and arguably simpler, but is available in fewer STM32 models
- I2S
- is available in more (but not all) STM32 models than the DAC
- means using an external I2S DAC - a little more work, yet gives you a choice of DAC to use
In theory you can also use PWM, because there a whole bunch of timers, but one of the above options is usually just a few bucks more and gives better quality and gives you more CPU to spend on what you want to generate.
Setup and programming
STM32Cube
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
STM32Cube is a group of applications intended to combine to be a complete toolset.
It includes things like
- STM32CubeMX [6]
- win, lin, osx
- "initialization code generator"
- generates a code to initialize the parts you want, for any known board - basically a template with all the hardware init, and an empty main()
- (and does things like calculating power use)
- You can then move to STM32CubeIDE, or other IDE/toolchain
- STM32CubeIDE [7]
- win, lin, osx
- STM32CubeProgrammer [8]
- flashing
- STM32CubeMonitor [9]
- run-time monitoring
- groups some more specific things (verify)
https://www.youtube.com/watch?v=hyZS2p1tW-g
STM32 Arduino
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
There are a handful of cores you can use, but mostly it's the following two:
- Arduino STM32
- since 2011 or so,
- STM32F1(03?) only, later also added STM32F4(verify)
- based on maple code (see also maple mini), not STM's code (because that wasn't released until years later), meaning new features take more work to add
- https://github.com/rogerclarkmelbourne/Arduino_STM32
- STM Core boards
- from STM, but came years later (2016, 2017ish)
- https://github.com/stm32duino
It seems that since the release of the latter, the former isn't really maintained anymore(verify),
and since a number of things differ, it's probably a good idea to choose the latter unless a specific codebase is easier to make work on the former.
There are others, but most were more specific than Arduino STM32
See also:
PlatformIO
Firmware flashing
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
RP2040 and Raspberry Pi Pico
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
RP2040 is a dual-core Cortex M0+, part of the Raspberry Pi Pico board and designed by Raspberry itself
- and available on a lot bunch of other boards[10]
- generally with USB-C connectors because it's a newer board
Comparisons it elicits
- Small ARM-based board - like SAMD21 based Arduino or Teensy LC.
- Pi Pico W may be an interesting alternative to the ESP8266 / ESP32 (and arguable somewhere between them)
Others
ESP8266, ESP32, etc.
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
See Electronics project notes/ESP notes
Haven't personally used" list
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
PIC
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
Comparable with AVR in many ways, has a wider range of choices and features, sometimes the more capable choice for a given project.
The main difference for starter hobbyists is that it lacks and Arduin-style standard board.
Also, people stick to what they already know, though, so for a large part, PIC people use PIC, AVR people use AVR.
nRF51, nRF52
Max32
Wiring
There is a Wiring board, made for the Wiring software.
The basic Wiring board is comparable to an Arduino Mega, with a few differences.
(sold e.g. here)
(MIT) HandyBoard
Based on (Freescale) 6811 microcontrollers (at 2MHz?)
...and cricket?
Parallax
http://www.parallax.com/ProductInfo/Microcontrollers/tabid/121/Default.aspx
Basic Stamp
https://www.parallax.com/microcontrollers/basic-stamp
Propeller
https://www.parallax.com/microcontrollers/propeller
BUG
PICAXE
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
http://www.rev-ed.co.uk/picaxe/
(NetMedia) BasicX (BX)
Forebrain
(Leaflabs) Maple
Computer-like
Some thin clients, netbooks, palm/pocket sized stuff
Effectively a middle way (in capabilities and price) between things like the beagleboard and a regular computer.
Often not so hip on the sort of IO you want in projects, but if you want an interface, particularly if a palmtop has a touchscreen, it's a lot easier to use a ready-made thing with an IDE for it than try to drive a tiny LCD from a microcontroller.
You may find options in the EUR/USD100-250 range, which often isn't a whole lot more than some dedicated-purpose devices, and can be a lot more flexible since they give you common interfaces and may let you run something general-purpose like linux.
At some point netbooks may become interesting, as from this perspective they are battery-backed, small and nicely boxed devices with built-in screens and start in this price range.
Currently often based on one of:
- Intel Atom[11] (x64)
- AMD's newer low-power chips (Competitors to Atom, CULV, and such), including Huron (Neo) and Geneva (Yukon and Nile refer to portable platforms that include the Huron and Geneva, respectively)
- VIA Nano[12] (x64)
- ARM7[16] (ARM architecture[17] is often used for specific-purpose embedded applications, and can be very good for their price)
- ARM9[18]
- ARM11[19]
- (ARM) Cortex
ARM processors span a wide range of speeds (stopping short of being part of the competitive netbook market, making it fit for various embedded and mobile uses. Quite a few phones use ARMs (often ARM11, occasionally ARM9), as do various tablets, the Nintendo DS
NVidia Jetson
Raspberry Pi
Comparable to a plug computer, but more like a real PC in use.
Architecture is ARM rather than x86, though.
Could run anything you can compile for ARM.
Which basically means linux. Some distros have tooling to make this easier, and often ready-made pi-specific builds (e.g. Arch, Debian).
Various hardware (e.g. WiFi, sound in) could be added via USB dongles, assuming the driver is compiled for ARM.
This initially excluded windows completely, but there is now an a Windows 10 for ARM (related to products like the Surface Pro X), and there is a project that helps install it on raspberry. Initially this meant only ARM apps (so basically none of yours), but now there is x86 and x64 emulation letting you run them, and it's not even that slow.
Driver support seems to also not be too bad.
Initial boot is from SD card((verify) - I've seen people boot it from M.2).
See also:
Board variants
First-gen (A or B)
- BCM2835 package, contains
- CPU: a 700 MHz ARM11 (ARMv6 arch)
- GPU: a Videocore 4
- USB
- SDRAM
- memory has been specced higher in later variants. 128MB, 256MB, or 512MB RAM (not physically upgradable)
- Composite video out
- audio out
- 3.5mm jack, PWM based rather than a DAC
- audio via HDMI
- the 26-pin is for the Arduinory crowd (there's also the VideoCore's JTAG, the USB/Ethernet chip's JTAG, but few will be interested in those)
- 3.3V (50mA limit), 5V (direct from power source)
- GPIO pins
- some of which have specializations like SPI, I2C, UART, PWM, JTAG
- Most can hook to interrupt handlers(verify)
- note that the exact layout has changed between board revisions. Pay attention.
Model A - above, but...
- no Ethernet
- just the one internal USB port
Model B - as above, but in the comparison to A and B+ ...
- 10/100 wired Ethernet (via USB2, so gigabit wouldn't make sense)
- uses a LAN9514 to serve USB2+FE (see e.g. this diagram for a Pi3) (also why this 100Mbit ethernet had share bandwidth with USB)
- Two USB ports (via on-board hub device)
- MIPI (for 15-pin camera interface. Not very usable yet?(verify))
Model B+: Like B, but...
- 14 more GPIO pins
- Four USB ports, better hotplug and overcurrent behaviour (much less likely to reset at USB insert)
- micro-SD slots instead of SD (and click instead of friction-lock)
- a little more power efficient (swithing regulator instead of a linear one)
- audio circuit less noisy
- composite video out is now part of the 3.5" jack, not a separate RCA plug (nor broken out elsewhere)
- It's a TRRS plug, with the ordering (from sleeve to tip) Video, Ground, Left Right -- see notes below.
Raspberry Pi Zero
- BCM2835 (same as 1st gen Pi, though clocked 40% faster)
- 512MB RAM
- smaller board, and GPIO pins come unpopulated to stay slim.
- USB/power via USB
- USB host port is also micro style, so you need a USB OTG cable to get that into a more standard USB A
- TV out is on two (unpopulated) pins
- On sound:
- Omits the headphone-jack-and-RC-filter (and a opamp buffer on B+ and 2 models) that the basic Pis have
- if you want, you can reproduce that externally, see e.g.
- HDMI sound is still there
- USB sound can be done cheap, but not all are supported, and quality of most cheap dongles still isn't great
- if you care about good quality analog sound, you want a decent DAC anyway (is available HAT-style)
Raspberry Pi Zero W
- like Zero, adds WiFi (11n) and bluetooth (4)
- (side note: this allows using a bluetooth keyboard/mouse instead of USB-OTG fiddling)
Raspberry Pi 2
- BCM2836, ARM Cortex-A7 (ARMv7 arch), 900MHz 4-core
- VideoCore 4 @ 900MHz
- CPU up to ~2x as fast as Pi1 B+
- 1GB RAM
Raspberry Pi 3 - mainly faster and more memory:
- BCM2837, ARM Cortex-A53 (ARMv8 arch), 1200MHz 4-core
- 1GB RAM (DDR2)
- WiFi (11ac, 2.4+5ghz)
- Bluetooth 4
Raspberry Pi 3+
- Ethernet+USB: Changed chips to a LAN7515 technically gigabit though in practice tops out at maybe 300Mbit, and is sharing with USB (verify)
- wifi is dual band: (verify)
- https://www.rs-online.com/designspark/raspberry-pi-3-model-b-vs-3-model-b
Raspberry Pi 4
- BCM2711, Cortex-A72 (ARMv8 arch) 1500MHz 4-core
- VideoCore 6 @ 500MHz
- 1/2/4GB RAM (DDR2)
- bluetooth 5
- wifi (11ac, 2.4+5ghz)
- adds USB3 (though with initial hiccups)
- VL805 for 2xUSB2, 2xUSB3
- ethernet port is gBit capable (switched to a BCM54213PE)
- dual video output / 4K res now at 60p
- reported issues:
- at maximum use the CPU you will likely hot enough to throttle, so you want some more cooling
- Powering from a proper USB-C power source has issues that can lead to a proper USB-C charger (sensibly) refusing to charge i.e. power it
Raspberry Pi Pico
- basically a fast microcontroller
- cheap
- little fancy IO
- sorta halfway between an arduino and raspberry - so not unlike a Teensy
- CPU: RP2040, Cortex-M0+ 133 MHz 2-core (for reference, see e.g. other boards using the RP2040)
- fairly overclockable - seems stable up to 250MHz(verify) (CPU can be pushed up to around 400MHz but peripherals start misbehaving, not least of which the external flash)
- 264 KB SRAM (internal)
- Pico has 2 MB of external flash
Notes on GPIO
Notes on power
For an idea of idle and loaded draw, see graphs like https://raspi.tv/2019/how-much-power-does-the-pi4b-use-power-measurements
The low end is mostly interesting for battery life.
Both are interesting for requirements on your power - e.g. Pi4 is harder to power from power banks or smaller wallwarts.
Pi1
- Model A specced for ~300mA max(verify)
- Model B for ~700mA max(verify)
- Zero ~250mA max (verify)
- Zero W ~350mA max (verify)
Pi2
- ~700mA max (verify)
Pi3
- ~800mA max (verify)
Pi 4:
- people have reported ~2A supplies tend to be good even under high CPU use (and something between 1A~2A under simple use)
- on paper worst case may be up to 3A
...plus whatever you draw through USB - powered USB hubs help here.
The Pi 3+ and 4(verify) have a PMIC, that detects and reports low voltage (under ~4.7V on its input), making it easier to diagnose insufficient power supplies.
See also:
- https://raspi.tv/2019/how-much-power-does-the-pi4b-use-power-measurements
- https://raspberrypi.stackexchange.com/questions/26526/current-draw-for-2-0-models/40393#40393
Saving power
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
tl;dr:
- Raspberries do not have anything like ACPI, so there is no sleeping
- you can turn it off completely (and may still use on the order of ~70mA then(verify)), but restarting it later will need something external
- Most power use, idle or max, seems to come from the overall system speed
- so has increased as generations have grown more powerful.
- which over/underclocking can barely change
- still lower when fairly idle, so try to minimize workload
So for a low-computational-load purposes, an older Pi (and note that Zero / Zero W are basically scaled down earlier-gen) can easily be the more power-efficient choice, and 4 the fastest/hungriest, see e.g.
- https://raspi.tv/2019/how-much-power-does-the-pi4b-use-power-measurements
- https://magpi.raspberrypi.org/articles/raspberry-pi-4-specs-benchmarks
That said:
For example, you can save
- anywhere from nothing to practically maybe 100mA by minimizing CPU use
- (that 100mA is arbitrary, less than the max-min use. I'm assuming you can optimize only so much, and am being optimistic)
- a little by disabling some peripherals you don't use (note: ability to do so varies a little per model)
HDMI
LEDs
WiFi, BT
USB and ethernet
CPU
The CPU is one of the larger power users.
The CPUs always did frequency scaling and, by default, fairly aggressively. So if you can do your work more efficiently, it'll put it near its lowest speed (baseline power user) more often (which is why idling in that graph linked above differs less than peak use differs). (disabling a few pointless background processes can also help, except they tend to not use much)
It turns out the effects from underlocking are small, (if you're using it fully you'ld just slow down the task, and if you're mostly idle you're not changing most of what that basic current draw comes from) and the undervolting need for that to make more of a dent may affect stability (of e.g. PCIe(verify)).
So the most effective thing you can do is lowering your workload.
Regulation
It seems that before 3+/4, the 3.3V rail came from a linear regulator, so you could get a slight win from replacing that with a switch mode 3.3V[21].
The 3+/4 switched to a switching MxL7704 PMIC, which you're less likely to beat.
The Zeros (and pre-+ 3(verify)) also seem to have a switch-mode (PAM2306).
TODO: read:
http://www.earth.org.uk/note-on-Raspberry-Pi-setup.html
https://www.raspberrypi.org/documentation/configuration/config-txt/overclocking.md
https://mlagerberg.gitbooks.io/raspberry-pi/content/5.1-power-consumption.html
https://community.roonlabs.com/t/underclocked-pi-4-the-perfect-low-budget-77-usb-bridge/93743/8
https://www.raspberrypi.org/forums/viewtopic.php?t=257144
https://www.jeffgeerling.com/blogs/jeff-geerling/controlling-pwr-act-leds-raspberry-pi
https://www.researchgate.net/publication/309917878
Notes on video out
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
The B+ has a 4-pin plug (a.k.a. TRRS, Tip-Ring-Ring-Sleeve) on which you can immediately use audio using a regular 3.5mm plug, while using composite video out (at all or alongside audio) will require a 4-pin (TRRS) plug.
Note that if you have a TRRS-to-four-RCA adapter cable, it can have a variant wiring. Often it just has two functions swapped (e.g. video and audio-right) so only requires a little trial and error. Sometimes it requires rewiring.
The behaviour of forced / auto-detection between HDMI and composite depends on settings in /boot/config.txt (see pages like this for reference if your config.txt doesn't have a lot of elaboration).
Mainly: If you want to force use of HDMI, even if it won't always be attached at boot:
hdmi_force_hotplug=1
If you want to force use of composite, even if HDMI is attached at boot:
hdmi_ignore_hotplug=1
Both these settings are 0 by (stock-)default.
edidparser edid.dat > edid.txt
(For CEA modes from that list, use hdmi_group=1, for DMT modes use hdmi_group=2)
If you want a resolution that is not in that list, look atIf you have a HDMI TV that wakes up when rebooting the Pi, that's because it sends an Active-Signal message. You can disable that:
hdmi_ignore_cec_init=1
When tweaking for your specific monitor, you may want to:
Some software won't send audio over HDMI unless you force it:
hdmi_drive=2
(1 is no sound, 'DVI mode')
Composite variants:
sdtv_mode=2
Where:
0 Normal NTSC 1 Japanese version of NTSC – no pedestal 2 Normal PAL 3 Brazilian version of PAL – 525/60 rather than 625/50, different subcarrier
And its aspect ratio - 4:3 is default
sdtv_aspect=1
Where:
1 4:3 (default) 2 14:9 3 16:9
You may wish to play with overscan, e.g.
disable_overscan=1
and e.g.
# larger, TV that shows more black border than you want: overscan_left=-10 overscan_right=-10 overscan_top=-30 overscan_bottom=-30
or:
# smaller, e.g. for a TV that removes too much of the edge by default: overscan_left=10 overscan_right=10 overscan_top=30 overscan_bottom=30
See also:
- http://www.raspberrypi.org/forums/viewtopic.php?f=28&t=82063]
- http://www.raspberrypi-spy.co.uk/2014/07/raspberry-pi-model-b-3-5mm-audiovideo-jack/
OMX
Notes on the videocore
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
VideoCore has parts like:
- VPU
- media coprocessor (think JPEG and H264 accel) (verify), so a a SIMD type thing (also 2 cores of it?)
- runs firmware (partly closed because licensing) that drives video acceleration, and 3D
- In typical use the VPU uses the QPU for OpenGL. the QPU is a 12-way(verify) SIMD, running a fairly fixed pipeline for fragment, vertex, and coordinate shading.
https://www.youtube.com/watch?v=eZd0IYJ7J40
https://github.com/hermanhermitage/videocoreiv/wiki/VideoCore-IV-Programmers-Manual
On SD corruption
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
HATs
HAT (Hardware Attached on Top) are are 65x56mm boards with a 2x20-pin header, following a spec[23] designed to make it standard-n-easy to connect hardware.
It has an autoconfiguration system based on an EEPROM, connected on the ID_SD (GPIO0) and ID_SC (GPIO1) pins (more details in the specs).
There are also HATs that don't even do the EEPROM stuff. (are these compliant?)
HATs are made for 40-pin-GPIO Pi variants, as of this writing A+, B+, 2, 3, 4, Zero.
Compliant HATs can often be made to work on 26-pin Pi variants, but won't configure automatically, because the EEPROM pins that assist that are among the 14 added pins.
Physically, if you want to use a HAT and access to the pins for other reasons, you'll probably want a female header with long pins.
HATs can, in general, not be stacked.
It was considered in the definitions, and can work in some specific cases, but it cannot be guaranteed, because pins could clash.
If there's no clash, or the HAT was designed to stack (e.g. with more of itself[24]) it'll work.(verify)
pHAT
A pHAT (partial HAT) is an informal variant, basically anything that doesn't meet the HAT specs physically or electrically.
Adafruit call them bonnets.
Also often means a smaller variant, sized like a Zero. It seems they typically tend not to have the EEPROM either.
Manual configuration / use, and many pHATs, can often me made to work - if all the pins they use are in the set of 26.
See also:
pHAT DAC notes
Seems to just use the 5V, ground and I2S pins (no EEPROM/I2C)
i.e.:
- Pin 2 (5V)
- Pin 12 (GPIO 18, I2S)
- Pin 35 (GPIO 19, I2S)
- Pin 39 (Ground)
- Pin 40 (GPIO 21, I2S)
http://forums.pimoroni.com/t/phat-dac-which-gpio-are-in-use/1388/9
https://pinout.xyz/pinout/phat_dac
https://learn.pimoroni.com/tutorial/phat/raspberry-pi-phat-dac-install
uHAT
Follows HAT standard (unlike pHAT), but have a smaller board.
Unsorted
LEDs, meaning and config: https://www.jeffgeerling.com/blogs/jeff-geerling/controlling-pwr-act-leds-raspberry-pi#:~:text=All%20Raspberry%20Pi%20models%20have,ACT%20(a%20green%20LED).
On 5V tolerance
Basically, No. The GPIO is all 3.3V and none of it is 5V tolerant.
The only exception seems to be MISO (Master In Slave Out)(verify)
To connect 5V to Pi GPIO, the simplest solutions are probably voltage dividers, sometimes a regulator, sometimes an optocouple, or one of a few diode tricks - see Electronics_notes/Changing_voltage#DC_level_shifting (but I need to write a better summary).
If you're going to go the current limiting resistor way (which, note is not ideal for fast communication, but plenty for slowish actuating signals), note that this suggests you should stay under 0.5mA, so the resistor should be over 10kOhm
Beagle
BeagleBone
Beagleboard
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
Wants 5V, consumes less than 2W.
Basic resources:
- 600MHz ARM processor
- 256MB Flash
- 256MB RAM
- GPU
- DSP chip
IO:
- USB socket for communication with host, and <500mA of power from it
- SD reader (MMC+/SD/SDIO)
- Sound (3.5mm input and output)
- S-Video / Composite video
- DVI-D (0n HDMI connector)
- USB 2 host, two ports
- JTAG header
- RS232 header
- (The CPU can speak I2C, SPI) (verify)
Costs EUR/USD~150
See also:
Plug computers
| This hasn't been updated for a while, so could be outdated (particularly if it's about something that evolves constantly, such as software or research). |
Sheevaplug, GuruPlug, Plug Computer 3.0
(from Marvell)
Sheevaplug (basic version)
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
From the outside, this looks mostly like a networked USB port.
Has:
- Low power ARM(-compatible) CPU, ~1GHz, draws only a few watts of power
- Gigabit Ethernet
- 512MB SDRAM
- 512MB Flash
- USB2 host
- USB socket with USB-to-serial connected to RS232 terminal, and the JTAG bus
- SD interface
Can run a few *nixes (ARM builds; there are some pre-made).
Commercial derivatives seem to include network file sharing, network backup, VoIP, and such.
USD/EUR ~100, depending on variant
Sheevaplug+ (a.k.a. eSata Sheeva)
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
Like the basic Sheevaplug, but adds an eSATA port
Guru Plug (a.k.a. Sheevaplug2)
Guru Plug Standard
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
- One Gigabit Ethernet port
- Two USB ports
- Wifi
- Bluetooth
- U-SNAP (Utility Smart Network Access Port) [26]
Guru Plug Server Plus
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
Much the same setup, but with:
- Two Gigabit Ethernet ports instead of one
- Two USB ports
- Micro SD
- eSATA plug
- Wifi
- Bluetooth
- U-SNAP [27]
GuruPlug Display
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
Like Server Plus, but
- 3 USB2 ports
- either a HDMI Port OR a Touch Panel Display
Plug Computer 3.0
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
PogoPlug
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
PogoPlug is a Sheevaplug derivative.
Comes with OS / firmware and PC-side software to go along. This This setup is for cloud-style, remote access, social-site sharing, with files tied to people and accounts. It can take files from USB (automounting and understanding FAT32, NTFS, HFS+, ext2, ext3), and has a decent interface.
That default setup does NOT do NAS in the sense of sharing files or media on a LAN with something like SMB/CIFS (a.k.a. windows file sharing), NFS, FTP, HTTP, DAAP, or such. The PC-side client makes files appear as if on a (new) local drive, which in itself is pretty handy - but only allows sharing with people with the same client and pogoplug accounts.
This all isn't a huge limitation. For one, you can enable ssh and install Samba on the existing setup within five minutes.
Tinkerers will like that it's an open-enough platform. You can install PlugApps (previously OpenPogo), which turns it into a generic linux server (but beware that not all hardware is necessarily supported, and driver stuff can be a pain).
Hardware:
- PogoPlug V1
- PogoPlug V2
- the fancier design, specifically the pink one (verify)
- 1.2GHz ARM
- 4 USB ports
- 256MB RAM
- 128MB Flash
- gigE networking
- PogoPlug Biz (mostly) seems to be the V2 hardware (verify)
- PogoPlug Pro (a.k.a. V3?)
- the fancier design, specifically the black one (verify)
- Not Sheeva-based
- armv6tel CPU (dual core CPU clocked to 700MHz) (verify)
- 128MB of RAM, 128MB of flash
- PCIE slot has 801.11 b/g/n WiFi (Pogoplug Video has some video transcoder hardware instead?(verify)) (later versions don't have PCIE?(verify))
- http://plugapps.com/index.php5/Hardware:_Pogoplug_Pro
See also:
- http://www.pogoplug.com/home-en-whats-pogoplug-product-comparison.html
- http://plugapps.com/index.php5/Portal:Hardware
PlugApps notes
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
Chumby
G20
NSLU, NSLU2
Popular for its price/ability balance, but has been discontinued.
You probably want to look to the #Sheevaplug now.
See also:
Router hacking (mostly for Linksys WRT54 and similar)
(See also Wireless notes)
Alternative firmware, and interfaces for them
- Tomato
- for wireless routers (broadcom)
- Perhaps most user-friendly for common uses (though less wildly configurable than some others)
- http://www.polarcloud.com/tomato
- OpenWrt
- for wireless routers
- http://www.openwrt.org/
- X-Wrt
- Extensions for OpenWrt
- http://www.x-wrt.org/
- Gargoyle
- Interface on OpenWRT (similar to X-Wrt in a number of ways)
- http://www.gargoyle-router.com/
- WIFI-BOX
- for wireless routers
- http://sourceforge.net/projects/wifi-box/
- DD-WRT
- FreeWRT
- (professional-market variant on OpenWRT)
- http://www.freewrt.org/
Router OS setups
- The Linux Router Project (LRP)
- Abandoned (see e.g. http://web.archive.org/web/20030624030005/http://www.linuxrouter.org/)
- LEAF Project (Linux Embedded Appliance Framework) (began as fork of LRP)
- Ipcop
- Zeroshell
- Meant to use most any computer (regular PC) as a router
- http://www.zeroshell.net/
- pfSense
- m0n0wall
- Floppy OSes (can be used for a HDD-less computer for firewall/NAT/other such purposes):
- floppyfw
- Fdgw (BSD)
Unsorted:
- Vyatta
- FREESCO
- CoovaAP
Some OpenWRT / X-WRT notes
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
Notes on the ports, switch, VLAN, wireless, and such
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
Note that details also vary per product, so while much of the below may apply, chances are that not everything does:
On many WRT54G and variants, you have
- five physical external ethernet ports (which are on the same internal switch)
- an internal link from the CPU to that switch
- an internal link from the CPU to the wireless device
The five external ports are functionally split into one marked 'internet' (meant to go to your gateway/modem), and four internal/lan. The internet port may be physically spaced differently, but sits on the same internal switch, and seen that way by the CPU because it mainly sees the switch device, which it (usually) calls eth0.
This is split by using VLAN (802.1q) tagging, which means that eth0 does not have an IP address, and routing rules involve the two vlan devices:
- eth0.0 (VLAN 0, the four basic ports (and the internal one))
- eth0.1 (VLAN 1, the internet port (and the internal one))
Note that since this is software-configured, this is just the default configuration you usually see. You can reconfigure this the way you want, e.g. merge all ports to use the thing as a plain switch, use multiple ports in a WAN-like way to use multiple broadband connections (probably each on their own VLAN) for redundancy, or whatnot.
The wireless device can also potentially get complicated, partially because of the way the hardware lets you emulate multiple wireless devices on a single physical device.
As such, you have a sort of dummy parent device, and one that you use in routing, often wlan0, which is connected to what to the CPU is eth1 (or eth2, or sometimes ath0, depending on product).
Further interfaces you may see include:
- br-lan exists when you put a device in bridging mode.
- imq0, imq1: InterMediate Queueing devices, which assist traffic control [28]
- monitor interfaces
How you want to configure the device varies, and OpenWRT and X-WRT don't assume they know what you want, so don't assist you much either.
Networks can be defined in any way on the various interfaces -- but it seems fairly easy to cause OpenWRT/X-WRT to be confused in terms of the routing it should do (I've seen various confused routing tables, though that also had to do with what I was trying to make it do).
The default configuration seems to often be lan+wireless bridged as 192.168.1.1/24, wan as dhcp. (verify)
(wifi is often bridged to LAN)
Notes on configuration notes
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
boot_wait and flashing
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
boot_wait makes it harder to brick your hardware, by always allowing you to flash it.
Somewhat simplified, it refers to a setting that the bootloader listens to. When enabled, the bootloader will wait for three seconds before trying to load the kernel. Within those three seconds (or, if the kernel image doesn't pass CRC check, indefinitely), you can send a new firmware image in via tftp at 192.168.1.1 (what the bootloader listens to, regardless of later config(verify)).
The boot_wait period starts fairly quickly after the device powers up, so timing matters. I like atftp since you can give a single command, and it'll do a few attempts, meaning you can start it off, then plug in the router, and just wait and see whether this attempt worked or not. Example command:
atftp --trace --option "timeout 1" --option "mode octet" --put --local-file file.bin 192.168.1.1
Failsafe startup
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
In OpenWRT, if you misconfigure the device and can't reach it, you probably want to start it in failsafe mode. This will cause the device to use some default configuration, such as taking 192.168.1.1 to be easily reachable on the LAN ports.
(Note: If you have another device that uses 192.168.1.1, you should disconnect it or you may cause some OSes and switches to become very confused about where to switch, which can break your network temporarily)
To do a failsafe startup: Yank out the power cord, plug it back in, and wait for the DMZ light to come on (signals the start of boot (verify)) to press the reset button on the back a few times (methods mention that the SES buttons should work too, but it didn't seem to for me. The amount of presses also seems to matter - not too often. My Random Superstition Procedure is three times in two seconds
Wait for the power/dmz to start blinking, and keep blinking (if it doesn't keep blinking, it's not in failsafe mode).
If it does, you can now reach the device through passwordless telnet (instead of the usual SSH) via one of the LAN ports, on 192.168.1.1.
What you want to do depends on what you did wrong. If you forgot your password, you want passwd. If you messed too much with all the settings, you can do a sort of factory-defaults thing using /bin/firstboot.
See also / unsorted links
http://sarwiki.informatik.hu-berlin.de/Programming_the_Linksys_WRT54GS_Wireless_Broadband_Router
http://x-wrt.org/ http://wiki.x-wrt.org/index.php/User_Manual http://wiki.x-wrt.org/index.php/Main_Page http://martybugs.net/wireless/openwrt/flash.cgi
https://dev.openwrt.org/ http://oldwiki.openwrt.org/
http://cyberforat.squat.net/openwrt/OpenWrt-HOWTO/x402.html
http://wiki.x-wrt.org/index.php/Multi-Route
https://forum.openwrt.org/viewtopic.php?id=13414
Some Tomato notes
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me) |
The WOL tool wants the MAC delimited using colons (as ether-wake does, and the value is fed straight to it)
