[HN Gopher] Linux on an 8-Bit Micro? (2012)
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Linux on an 8-Bit Micro? (2012)
Author : craigjb
Score : 42 points
Date : 2020-12-21 18:23 UTC (1 days ago)
(HTM) web link (dmitry.gr)
(TXT) w3m dump (dmitry.gr)
| kube-system wrote:
| > This is definitely not the fastest, but I think it may be the
| cheapest, slowest, simplest to hand assemble, lowest part count,
| and lowest-end Linux PC.
|
| Amazing to think that 8 years later these ATMegas are _more_
| expensive than some of the SoCs currently on the market in
| production linux devices.
|
| https://hackaday.com/2018/09/17/a-1-linux-capable-hand-solde...
| dragontamer wrote:
| Yeah, but those Linux SoCs don't have a ADC or accurate PWM
| timers.
|
| You cam probably beat an ATMega with a STM32 of some kind. But
| the embedded world is more about simplicity of connecting to
| ADC / PWM / I2C and other such functionality. But even vs STM,
| ATMega supports 5V and full static (0Hz clock) operation.
|
| You're not looking at MHz or RAM when you buy a
| microcontroller. You're looking at connectivity (which STM
| delivers... but there's still an ATMega / Arduino legacy
| advantage from a code perspective).
|
| ----------
|
| 20 years ago, plenty of people were making fun of 8051 boards
| that cost $100 but provided only 12MHz of clock and 256-bytes
| of RAM (not kB, literally bytes). The PC-market / high-level
| programmers always underestimate the importance of connectivity
| and overemphasize specs.
|
| Embedded is mostly fine with 20MHz clocks: and arguably prefers
| less power usage (so things like "static 0Hz operation" are big
| features). Having an ATMega run at 100kHz clock rates for
| maximum power-savings but still providing the functionality you
| need (ie: Timers / ADC / etc. etc.) is pretty useful.
|
| Or ATMegas can accept unregulated 5V, and just running off of
| USB-power (which can be between 4.5V to 5.5V in practice,
| exceeding the specs of STM32 chips). That simplifies the design
| of your board, since you don't need a buck-converter to go from
| 5V unregulated USB to 3.3V on the STM32.
| duskwuff wrote:
| > You cam probably beat an ATMega with a STM32 of some kind.
|
| You can run Linux _directly_ on some STM32 MCUs. No emulation
| required!
|
| https://github.com/torvalds/linux/tree/master/arch/arm/mach-.
| ..
|
| That being said, static operation is really less of an issue
| than you're implying. Modern MCUs can _idle_ (not sleep!) at
| under a milliamp; it 's not difficult to get them to draw
| less average current than the leakage current of their
| battery. The lack of 5V operation is a little annoying in
| some scenarios, but is easily worked around with a 3.3V LDO
| -- which is frequently required anyway for interoperability
| with other components. (A switching converter is hardly
| necessary for a USB device drawing a couple milliamps.)
| dragontamer wrote:
| > it's not difficult to get them to draw less average
| current than the leakage current of their battery.
|
| Well... depends on the battery. A bog-standard AA Alkaline
| battery has 2500 mA-hr (from 1.5V to 1V, @100mA draw:
| https://data.energizer.com/pdfs/e91.pdf), and have a
| ~3%/year self discharge rate. That's a leakage current of
| 75mA-hrs / year, or ~10 uA if I did my math correctly.
| Lithium, and watch button batteries (Silver) leak even
| less!
|
| ATTiny 1607 is specified at 6uA at 1.8V @ 32kHz active mode
| (though 5V barely is any more current). It looks like
| STM32G031J4 is ~20 uA at "low-power mode" @ 1.8V 32kHz (a
| special mode below 2MHz). Which is a lot better than I was
| expecting. (Note to others who may not know this: this is
| likely a Cortex-M0+ design only. Typical ARMs will not be
| able to reach this low level of power. Heck, larger STM32
| Cortex-M4 processors probably have a much higher minimum
| clockrate)
|
| Both chips are ~200 uA at 2MHz, Which gets you to ~500 days
| of continuous operation from 2500 mA-hr AA.
|
| ------
|
| Yeah, there's a bunch of batteries that self-discharge in
| just 3-months. But... alkaline AA exist for a reason! Low-
| self discharge, and they're actually really good at these
| milliamp/microamp levels of current. And again, its all
| about those silver-watch batteries or lithium-watch
| batteries if you really want the lowest self-discharge in
| the market. (~5 years per silver-watch battery, but you
| need to draw stupidly low amounts of current).
|
| It seems like the ATTiny 1607 still has a superior sleep
| mode compared to STM32G031J4, so if you're sleeping most of
| the time on a watch battery, maybe ATTiny wins.
|
| I do agree with you though: it does seem like STM32 has
| really dropped their power down a lot. I don't know if
| STM32 always supported 32kHz clock rates however, I seem to
| remember them having a higher minimum clock rate last time
| I checked this out. Lowering those clock speeds really
| helps at minimizing power. And I expect AA-batteries to be
| the typical size of most people's hobby projects.
|
| I dunno if "full static" is really needed, since 32kHz is
| still really, really low power. It seems nice that ATTiny /
| ATMegas hve 0Hz as an option (maybe if an external
| temporary clock turns on only occasionally in a power-
| constrained environment).
| magicalhippo wrote:
| > The lack of 5V operation is a little annoying
|
| It should be noted many STM32's (if not all, huge family)
| have 5V tolerant I/O pins, so it's not nearly as annoying
| as it could be.
| kube-system wrote:
| For sure. I still prefer tinkering with my Arduino to my
| Raspberry Pi, because the electronics side of things is way
| easier.
| SomeoneFromCA wrote:
| You should never run microcontroller from an unregulated
| supply - it will brown out. USB is not unregulated, it just
| has bad precision, but regulation I am sure is pretty fine.
| corgihamlet wrote:
| https://www.wired.com/2004/10/os-x-on-a-68k-c/
| simonblack wrote:
| Seems two hours or thereabouts is the sort of 'standard time' for
| 8-bit micros to reach a bash prompt. That's been the case for
| about 10 years.
|
| Nevertheless, that's still a fantastic achievement. And the ARM
| emulator makes it even more so.
| ajfjrbfbf wrote:
| What does he mean by ARM emulator? Does it mean translating
| from ARM instruction set to AVR's? If so what is the 6.5 kHz
| about? An ATmega can probably run at a few MHz, surely
| emulating 32-bit instructions from 8-bit doesn't take a
| thousand cycles on average.
| dmitrygr wrote:
| > surely emulating 32-bit > instructions from 8-bit
| > doesn't take a thousand > cycles on average.
|
| It does if you do it in C, and also need to emulate the mmu
| and permission checks. Plus arm's instructions do a lot. A
| free arbitrary 32-bit shift in every instruction is hard on
| an 8-bit device which can only shift 8 bits by one bit per
| instruction. You end up with a lot of loops, and loop control
| instrs kill perf there.
|
| The fact that I had to _bit-bang_ the memory interface also
| does not help as the avr device has no dram controller
|
| I had, at some point, rewritten the core in avr assembly for
| a large-ish speedup, but i never got around to publishing it.
|
| Currently i am working on a TTL-built 1-bit computer, unto
| which i want to port this emulator, so boot linux on a 1-bit
| computer :)
| avmich wrote:
| > 1-bit computer
|
| I've really enjoyed RISC V serial (SERV) presentation -
| 1-bit computer essentially. Wonder how low one can get in
| terms of transistor count, without going the path of
| LGP-30.
| retrac wrote:
| At that point, you probably do just want to go the path
| of the LGP-30. The registers are the most expensive part.
| While you could move them into RAM, that has the same
| performance cost as an accumulator machine, with more
| control complexity. If you were considering RISC (without
| compression, anyway) then you're likely not heavily
| pressed for code density to begin with. It probably could
| be done in under 100 gates, excluding the shift
| registers.
| moring wrote:
| Since you are already using TTL parts -- would peripherals
| build from them (or similar discrete gates with whatever
| voltage levels you'd need) help to speed up the ARM
| emulator? I'm asking this because I'm actually not sure if
| such a thing would be faster than even bit-banging on the
| AVR. But I could imagine that things like the memory
| interface would benefit from a "hardware" implementation.
| dmitrygr wrote:
| Current plan is no special interfaces. Just 8 input and 8
| output pins controllable via special instrs.
| dragontamer wrote:
| Don't underestimate the 1-bit computer!!
|
| One of the most popular SIMD computers in the late 80s was
| the CM-2: a 4096x wide 1-bit computer. All SIMD-
| instructions.
|
| So it can definitely be used "seriously".
| contingencies wrote:
| So today in theory according to https://elinux.org/STM32 you can
| buy an STM32F4 board which costs about 100RMB (USD$15) including
| external ethernet PHY and SD card and run Linux on it. It looks
| like STMicro is seeking a very competitive price point for
| STM32F407 class chips right now and you get USB OTG, camera, etc.
| as well as "more RAM than anyone will ever need". I would like to
| see that.
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