The Pine64 folks have given us so many tasty pieces of hardware over the last few years, but it’s fair to say that their products are for experimenters rather than consumers and can thus be a little rough around the edges at times. Their Clusterboard for example is a Mini-ITX PCB which takes up to seven of their SOPINE A64 compute modules, and networks them for use as a cluster by means of an onboard Gigabit Ethernet switch. It’s a veritable powerhouse, but it has an annoying bug in that it appears reluctant to restart when told. [Eric Draken] embarked upon a quest to fix this problem, and while he got there in the end his progress makes for a long and engrossing read.

We journey through the guts of the board and along the way discover a lot about how reset signals are generated. The eventual culprit is a back-EMF generated through the reset distribution logic itself causing the low-pulled line to never quite descend into logic 0 territory once it has been pulled high, and the solution an extremely simple application of a diode. For anyone who wishes to learn about logic level detective work it’s well worth a look. Meanwhile the board itself with its 28 ARM cores appears to have plenty of potential. It’s even a board we’ve mentioned before, in a personal supercomputer project.

4 thoughts on “An Epic Tale Of Reset Line Detective Work”

1. Allan-H says:
   August 1, 2021 at 12:28 am

   Pro tip: do not use 1A Schottky diodes for isolating primary cells. The reverse current through the diodes can be quite large, typically exceeding the maximum charging current for the cell (which may be significantly less than 1uA (depending on the cell)). One of the example schematics on that page used a CR2032, which isn’t a large cell and won’t handle reverse current.

   To pass any reasonable safety test (e.g. UL), you’ll need something to limit maximum discharge current (a resistor) and at least two things (e.g. diodes) to prevent reverse (charging) current. The whole idea is that there will not be a fire even if some components on the board mysteriously develop shorts.

   Reply
2. rtyhrtyrt says:
   August 1, 2021 at 1:29 am

   poor equipment cooling. They should build it vertically like a chimney

   as for the reset, I wonder if it is possible to reset just one module or a random one?
   shutdown -how_many 3 or 20% ;)

   Reply
3. jawnhenry says:
   August 1, 2021 at 10:19 am

   It is really good to see an article–any article– on the Pine organization; thank you very much. The Pine organization has taken quite a bit of unwarranted flack for not being a “production house”, whatever that means, nowadays. There are quite a few “production houses” which should be as professional as the Pine organization.

   From Ms. List:

   ”…but it’s fair to say that their [Pine 64] products are for experimenters rather than consumers and can thus be a little rough around the edges at times…

   Pine is VERY up-front about this, unlike a LOT of other “vendors”. From Pine’s very own web-site, in their very own words…

   “…This is the Beta Edition of the PinePhone. The pre-installed Manjaro with Plasma Mobile OS, that ships with this edition of the PinePhone, is a beta software build. This effectively means that while core functionality of the PinePhone still an ongoing effort. Thus, the device cannot considered a consumer-ready product.”

   ….and…

   “Beta Edition PinePhones are aimed solely at early adopters. More specifically, only intend for these units to find their way into the hands of users with extensive Linux experience.”

   …and…

   “DISCLAIMER
   A small numbers of stuck or dead pixels (1-3) can be a characteristic of LCD screens. While rare, this should not be considered a defect. If you think that a minor dissatisfaction, such as a dead pixel will prompt you to file a PayPal dispute, DO NOT purchase the PinePhone. When fulfilling your purchase, please bear in mind that we are offering the PinePhone at this price as a community service to PINE64 community. Thank you.”

   I, personally, read all their blogs so that I’m aware of all “warts”. I also intend to purchase the Pinephone–one of THE most secure, privacy-capable, AND Linux-OS-running phones available from anywhere or anyone–just as soon as the hardware keyboard option is released to production–and it is very close. Oh, and it’s one of THE most hackable and repairable of phones (the keyboard option is “do-able” because of six “pogo pins” built onto and into to motherboard; battery?–replaceable with a very standard Samsung 3000 mAH unit.

   [From Jenny List–“Their Clusterboard for example is a Mini-ITX PCB which takes up to seven of their SOPINE A64 compute modules, and networks them for use as a cluster by means of an onboard Gigabit Ethernet switch. It’s a veritable powerhouse…”.

   It is my understanding that Pine is so confident in their product that they “eat their own dog-food”, insofar as that they have built their own server–based on this hardware–on which their entire website operates. Could be wrong. Won’t be the first, or last, time…]

   Thank you, Jenny.

   Reply
4. Greg A says:
   August 1, 2021 at 6:01 pm

   i read the whole thing because i wanted to understand the failure itself but i find i still do not. the assumption appears to be that a 74LVT04 (quad not) which is simply used as a dual buffer somehow experiences “back EMF” and draws more than 60 mA, sending the PMIC into a bad state? i don’t understand where this current draw would come from. i thought back EMF was a property of inductors. it doesn’t seem realistic to me that the transient draw of a 74LVT04 switching its own input gate would draw current for long enough to matter, and i don’t understand why its downstream consumer would draw more than 60mA. i don’t understand.

   can someone explain it to me? i’m tempted to think that the author doesn’t know any more than i do and has just found a superstitious unknown that allowed him to make a blind hack that happens to work….but my own ignorance is pretty deep.

   Reply

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