Monday, November 23, 2015

Using ser2net for serial access.

Is your table a mess of wires? Do you have multiple devices connected via serial and can't remember which is /dev/ttyUSBX is connected to what board? Unless you are a embedded developer, you are unlikely to deal with serial much anymore - In that case you can just jump to the next post in your news feed.

Introducting ser2net

Usually people start with minicom for serial access. There are better tools - picocom, screen, etc. But to easily map multiple serial ports, use ser2net. Ser2net makes serial ports available over telnet.

Persistent usb device names and ser2net

To remember which usb-serial adapter is connected to what, we use the /dev/serial tree created by udev, in /etc/ser2net.conf:
# arndale
7004:telnet:0:'/dev/serial/by-path/pci-0000:00:1d.0-usb-0:1.8.1:1.0-port0':115200 8DATABITS NONE 1STOPBIT
# cubox
7005:telnet:0:/dev/serial/by-id/usb-Prolific_Technology_Inc._USB-Serial_Controller_D-if00-port0:115200 8DATABITS NONE 1STOPBIT
# sonic-screwdriver
7006:telnet:0:/dev/serial/by-id/usb-FTDI_FT230X_96Boards_Console_DAZ0KA02-if00-port0:115200 8DATABITS NONE 1STOPBIT
The by-path syntax is needed, if you have many identical usb-to-serial adapters. In that case a Patch from BTS is needed to support quoting in serial path. Ser2net doesn't seems very actively maintained upstream - a sure sign that project is stagnant is a homepage still at This patch among other interesting features can be also be found in various ser2net forks in github.

Setting easy to remember names

Finally, unless you want to memorize the port numbers, set TCP port to name mappings in /etc/services:
# Local services
arndale            7004/tcp
cubox              7005/tcp
sonic-screwdriver  7006/tcp
Now finally:
telnet localhost sonic-screwdriver
^Mandatory picture of serial port connection in action

Friday, September 4, 2015

Migration to Scaleway ARM server

The C1 Server

Scaleway started selling ARM based hosted server in April. I've intended to blog about this for a while, since it was time to upgrade from wheezy to jessie was timely, why not switch provider from an X86 based to ARM one at the same time?

In many ways scaleway node is opposite to what "Enterprise ARM" people are working on. Each server is based on an oldish ARMv7 Quad-Core Marvell Armada XP, instead of a brand new 64-bit ARMv8 cpu. There is no UEFI, ACPI or any other "industry standards" involved, just a smooth web interface and a command line tool to manage your node(s). And the node is yours, it's not shared with others with virtualization. The picture above is a single node, which is stacked with 911 other nodes into a single rack.

This week, the C1 price was dropped to a very reasonable €2.99 per month, or €0.006 per hour.

Software runs on hardware, news at 11

The performance is more than enough for my needs - shell, email and light web serving. dovecot, postfix, irssi and apache2 are just an apt-get away. Anyone who says you need x86 for Linux servers is forgetting that Linux software is open source, and if not already available, can be compiled to any architecture with little effort. Thus the migration pains were only because I chose to modernize configuration of dovecot and friends. Details of the new setup shall be left for another post.

Friday, June 12, 2015

Dystopia of Things

The Thing on Internet

I've now had an "Internet of Things" device for about a year. It is Logitech Harmony HUB, an universal remote controller. It comes with a traditional remote, but the interesting part is that it allows me to use my smartphone/tablet as remote over WiFi. With the android app it provides a rather nice use experience, yet I can see the inevitable end in anger.

Bare minimum GPL respect

Today, the GPL sources for hub are available - at least the kernel and a patch for busybox. The proper GPL release is still only through written offer. The sources appeared online April this year while Hub has been sold for two years already. Even if I ordered the GPL CD, it's unlikely I could build a modified system with it - too many proprietary bits. The whole GPL was invented by someone who couldn't make a printer do what he wanted. The dystopian today where I have to rewrite the whole stack running on a Linux-based system if I'm not happy what's running there as provided by OEM.

App only

The smartphone app is mandatory. The app is used to set up the hub. There is no HTML5 interface or any other way to control to the hub - just the bundled remote and phone apps. Fully proprietary apps, with limited customization options. And if app store update removes a feature you have used.. well you can't get it from anywhere anymore. The dystopian today where "Internet of Things" is actually "Smartphone App of Things".

Locked API

Maybe instead of modifying the official app you could write your own UI? Like one screen with only the buttons you ever use when watching TV? There *is* an API with delightful headline "Better home experiences, together". However, not together with me, the owner of the harmony hub. The official API is locked to selected partners. And the API is not to control the hub - it's to let the hub connect to other IoT devices. Of course, for talented people, locked api is usually just undocumented api. People have reverse engineered how the app talks to the hub over wifi. Curiously it is actually Jabber based with some twists like logging credentials through Logitech servers. The dystopian today where I can't write programs to remotely control the internet connected thing I own without reverse engineering protocols.

Central Server

Did someone say Logitech servers? Ah yes, all configuring of the remote happens via myharmony servers, where the database of remote controllers lives. There is some irony in calling the service *my* harmony when it's clearly theirs. The communication with cloud servers leaks at minimum back to Logitech what hardware I control with my hub. At the worst, it will become an avenue of exploits. And how long will Logitech manage these servers? The moment they are gone, harmony hub becomes a semi-brick. It will still work, but I can't change any configuration anymore. The dystopian future where the Internet of Thing will stop working *when* cloud servers get sunset

What now

This is not just the Harmony hub - this is a pattern that many IoT products follow - Linux based gadget, smartphone app, cloud services, monetized apis. After the gadget is bought, the vendor has little incentive to provide any updates. After all, the next chance I'll carry them money is when the current gadget gets obsolete.

I can see two ways out. The easy way is to get IoT gadgets as monthly paid service. Now the gadget vendor has the right incentive - instead of trying to convince me to buy their next gadget, their incentive is to keep me happily paying the monthly bill. The polar opposite is to start making open competing IoT's, and market to people the advantage of being yourself in control. I can see markets for both options. But half-way between is just pure dystopy.

Wednesday, April 22, 2015

Fastest way to change running dtb

Tollef posted about using BeagleBone Black for temperature monitoring. There was a passage about patching the DTB (device tree) file:
... This needs to be compiled into a .dtb. I found the easiest way was just to drop the patched .dts into an unpacked kernel tree and then running make dtbs.
There are easier ways. For example, you can get the current device tree file generated from /proc:
apt-get install device-tree-compiler
dtc -I fs -O dts -o current.dts /proc/device-tree/
(Why /proc and not /sys ? because device tree predates /sys) Now you can just modify and build the dtb again, and install it back to where bootloader reads the dtb from:
vim current.dts
dtc -I dts -O dtb -o new.dtb current.dts
Alternative, of course, is to build a brand new mainline kernel and use the dynamic Device tree code now available.