The Freescale "Freedom" FRDM-KL25Z boards have a lot going for them. They're cheap ($13), and sport an ARM Cortex M0+ core in an Arduino-ish form factor, with a fancy "OpenSDA" USB-based flash/debug thingey bolted onto the side for user-friendlieness.
Unfortunately.. they botched the execution in many ways; some subtle, some less so.
Let's start with the first impression. In order to get anything more useful than marketing materials from Freescale's web site, you have to register. They then hand this info off to a distributor who proceeds to email and call you before you have a chance to meaningfully evaluate anything.
The actual datasheets and programmer manuals were okay; not the worst I've seen by any means, but not all that great either.
But the software side of things is another story. The only thing they offer is a ginormous plugin for an obsolete version of Eclipse that supports all of their microcontrollers... via a code generator. Theoretically, once you generate that skeleton codebase it's usable outside of Eclipse.
At least you can extract the not-quite-CMSIS-compliant processor headers from that morass. But those files say "all rights reserved" which makes them technically unredistributable. Sigh.
But the best part, the part I spent the last day and a half fighting, was their "OpenSDA" programming/debugging mechanism.
In theory, it's a smart design -- It presents as a composite USB device consisting of a serial port and a virtual mass storage device. The serial port gives you the console, and to program the controller's flash, you just copy a new firmware image over to the filesystem.
It turns out there's nothing open about it.
OpenSDA is about as proprietary as it gets. To actually use it as a debugger under Linux you'll need a proprietary 32-bit-only binary drivers+libraries. That's right, they don't even supply an application to use it -- even a GDB server will cost you extra.
So it's useless as a debugger. What about as a flasher/programmer? It fails even more spectacularly there, thanks to it simply not working under Linux (or even OSX), due to gross violations of the USB mass storage spec.
In all fairness, they did eventually fix these problems (both in their bootloader and their flasher "application").. but you'll still need a native Windows system (not a VM, because their USB enumeration is just that badly broken) to do the update. Once you have the new application running, it works well enough, though it doesn't complain if you try to write something too large.
The one saving grace is that Keil released a firmware file that replaces the anything-but-OpenSDA "flasher+debugger" with ARM CMSIS-DAP compliant interface that JustWorks(tm). Unfortunately, it's only usable as a debugger with the tools I have, so to actually flash an image, you have switch back to the OpenSDA "applications" -- which, since they pulled their fixed-for-Linux bootloader, requires a Windows box.
All I want to do is write a "Hello World" program on this thing, and I've wasted the better part of two days on things that should JustWork(tm).
So much to "Open" or "Freedom" -- Grand ideals ruined by horrible execution. Unfortunately, this is the sort of thing I've come to expect out of Freescale. Every encounter leaves me wanting to bash my head againt the wall.
A month or so ago I compared Freescale to someone shooting themselves in both left feet. Maybe I should add "while running backwards" to that analogy.
In comparison, STMicro's STM32F4DISCOVERY board ($15 with a Cortex-M4!) isn't without its flaws, but it took less than half an hour to assemble everything I needed to flash and debug the board, and their documentation and software samples are comprehensive and excellent.
...It's not much of a race.