Category Archives: documentation

oh udev. oh yes

Posted by KarlP on 25 May, 2016 None comments

I try and do the “right thing” when it comes to the future and how linux distros see their roles and the way things should be.  I think systemd has some generally good ideas, though I think upstart has far far better documentation.  Anyway, given that linux distros still “protect” users from plugging in usb devices, except for all those ones that they _don’t_ protect you from, if you’re working with embedded electronics, sooner or later you need to “fix” permissions for some device you have.  No matter, the canonical advice for a “long time” has been something like adding a file in /etc/udev/rules.d/doesnt_really_matter.rules with some content like…


ATTRS{idVendor}=="aaaa", ATTRS{idProduct}=="bbbb", GROUP="plugdev"

And you added yourself to the plugdev group, and everything was pretty much ok. Now, it’s the “future” and we can’t use anything so silly and outdated as groups to assign permissions. Heaven help us, what would become of us all if people just used groups?! Now we need to use “tags” and a magical “uaccess” incantation. Except for all those devices that we do use groups for, like usb modems, usb serial ports, usb printers, wireshark capture permissions, virtualization, colour correction devices, basically everything except “unknown” devices.

But ok, good and well, we’ll learn the new magic incantation for udev….

ATTRS{idVendor}=="aaaa", ATTRS{idProduct}=="bbbb", TAGS+="uaccess"

And…. it doesn’t work. Why? Good fucking luck finding out. If you’re lucky, someone might suggest that the name of your file isn’t right. Why should that matter? Welllll. because it does. See https://lists.freedesktop.org/archives/systemd-devel/2015-August/033946.html and https://bugzilla.redhat.com/show_bug.cgi?id=1074122#c0 for some hints and clues.

TL;DR: pretty much must be named 70-doesnt-matter.rules. At least until system decides that it should be a different number without documenting it anywhere.

SiLabs EFM32 Happy Gecko starter kit – first impressions

Posted by KarlP on 11 August, 2015 None comments

More unboxing. It includes a CR2032 coin cell in the box. Handy when the product line’s premise is ultra low power. It includes two usb cables, one mini, one micro. What the hell. why are you using mixed connectors?! (One for debug, one for user, similar to the original STM32F4 discovery)

Nice looking board, nice screen. Factory demo software is space invaders! Nice demo of touch buttons, physical buttons and the screen. Startup screen shows the debugger state as well. Expansion header seems to have a full silkscreen with correct positioning. Debug connector for connecting your own debug hardware is the full ARM Cortex with trace header, 2×10@1.27mm pitch. This is somewhat unusual, I’ve never had one that broke out the full ETM pins.

The kit user guide implies that there’s a USB flash drive in the box, containing simplicity studio. Thankfully that’s not the case. That would have been really wasteful. (Yes, yes, helpful for some people with shitty internet, but incredibly wasteful for everyone else)

The onboard JLink OB also presents a mass storage device, with a (broken) mbed link, a link to the starter kit’s home page, and a link to simplicity studio’s homepage. Rather shitty filenames, but I guess that helped someone’s day :) Bit lame about the mbed link not working though. It looks like something that mbed setup to be permanent, but someone overlooked somewhere: http://mbed.org/device/?code=200501120000B7A4D74B847B (Update: It might actually work, but mbed’s website was hacked at the time of writing….)

The rest of the kit user guide doc is rather sparse, (to be polite) simply containing some screenshots of how to run demos and get more information from within Simplicity studio. The kit home page does have a link to download the schematics though, that’s nice.

Doesn’t work with OpenOCD at the time of writing, but very basic preliminary support is proposed in http://openocd.zylin.com/#/c/2931/

Atmel SAMD10 Xplained mini board review

Posted by KarlP on 11 August, 2015 2 comments

Got a pile of dev boards for some testing. Some first impressions of the ATSAMD10-XMINI. First off, it’s nice and cheap, $9 or so. Comes in a really small cardboard box, with absolutely no documentation beyond some links on the box. Totally fine, no need for anything else these days. The board is a somewhat unusual shape, with the micro usb connector for the onboard DDBG (CMSIS-DAP) protruding out the back. Whatever. At first glace, the board appears well labelled. A closer glance….. well…

The user guide for this board refers to all the headers as JXXX. The J number is NOT in the silk on the board. The userguide has a picture of the board, and marks some of the J headers, but not all. The rest you have to just sort of figure out. This seems like a really amateur oversight. Fixing the silk would have been ideal, but at least the documentation could have a better overview of the board! (The userguide does manage to include screenshots of how to install atmel FLIP, which seems like a total waste of space for this document)

The user guide refers to the pins with J200-1, -2, -3, etc. The silk on the pad arrays is just numbered 1..5, and A..P. There’s silk on the back describing some pins, no idea why some and not others. There’s a big box of silk on the back that seems to be describing some pins, but no idea which, or what order.

There’s a specially boxed off section of pads in the top right, 2×10. It’s unlabeled. No idea what it’s for. (Update, turns out this is for Xplained Pro addons, the userguide covers this, and actually uses the grid array notation that matches the board.)

The user guide does (un)helpfully include arduino pin numbers, for the arduino compatible pin arrays, but there’s no mention of arduino software, or linked anywhere, so who cares about that. The column in the table that includes this is unlabeled as well.

The factory firmware is a morse application. Connecting to the CDC-ACM uart provided by the EDBG module lets you blink out letters, and tapping in keys on the user button prints them to the uart. It resets every few seconds idle and prints some help text. Neat enough.

The user guide does NOT include the schematic of the board. This is a serious omission. Particularly given the poor documentation/silk screen match up, but also as these boards are often used as examples for your own projects. A snippet of the power supply section is included, but again, the labels don’t match the board. I went back and forth through the user guide a few times to make sure I wasn’t missing anything. However, the software package download, which I skipped initially, actually includes no software. It includes all the schematics and proper board diagrams that should have been in the user guide. Pretty poor form Atmel :|

No comments on the tools or device itself yet, that’s for a much later date :)