In “A Shell for the Freedom KL25Z Board” I have presented an application which implements FreeRTOS, LED’s and a shell using the UART on the KL25Z over OpenSDA. So why not adding native USB CDC to the mix? Using both the USB and CDC with the same shell?
So what I have added is that the shell runs on both the SCI (over OpenSDA) and USB CDC (with the KL25Z). For this, the FSL USB CDC software stack is now part of the project:
Shell Project with USB CDC
Checking the download statistics of my Processor Expert components on http://www.steinerberg.com/EmbeddedComponents/, there is a clear winner: FSL_USB_Stack 🙂
It has been a while I presented that universal USB CDC component in this blog. The component has received a larger re-architecture, I wanted to support more than just USB CDC. For this, the CDC part is now present in a separate sub-component:
FSL_USB_Stack with Sub-Components
In “Optimizing the Kinetis gcc Startup” I stripped down the fat of my startup code. Now time to add some useful things. And what does a microcontroller like the KL25Z on the Freedom FRDM-KL25Z board have: Pins! And this means I have bits to set and read :-).
FRDM-KL25Z Board
The GNU gcc tool chain integration in CodeWarrior/Eclipse MCU10.3 has a nice feature to show the code and data size of my application after linking (see this article how to enable this). So if I create an ’empty’ project with the wizard, get the code and data size without consulting the linker map file:
Console View with Code and Data Size
But wait! 2604 bytes of code for almost doing nothing? That’s not what I want! There are ways to get that puppy much, much slimmer. Down to 284 bytes 
.
There are several reports in the Freescale forums around having ‘secured’ the Freedom board. But what does ‘securing’ a board mean? And what does it mean if I get that ‘Device is Secure’ dialog?
Device is Secure. Erase to unsecure?
There are different levels of protection you can find in many embedded microprocessors, and the terms might vary from vendor to vendor:
Many compilers offer a way to allocate a variable at an absolute address. For example for the Freescale S08 compiler, I can place my variable at a given address:
unsigned char buf[128]@0x2000;
This is very useful (and needed) e.g. if the hardware (like USB) needs a buffer at given address. The advantage of the above (non-ANSI and thus not portable) syntax is that I can define a variable at an absolute address, without the need to allocate it in the linker.
I wanted to do something similar with gcc for Kinetis/ARM, and searched many forums on the internet. Obviously, I’m not alone with this question. The solution I have found comes close to what I use e.g. for the S08 compiler.
The ARM Cortex-M0+ on the KL25Z Freedom Board (FRDM-KL25Z) runs up to 48 MHz. For this, the 8 MHz crystal on the board is used. A 48 MHz is required for USB communication, to have the needed oversampling on USB data lines. I have shown in my USB CDC post how such a clock is configured, using the white pre-production board. To my surprise, when I tried the same code on the black production boards, it did not work on the production black boards. Even worse: it worked on some, but not on every board :-(.
In ‘Device is Secure‘ I had a case where this was a false alarm. But recently there has been a report in the Freescale Forum that this can be a real problem with the Freedom KL25Z board I’m using too. I was not able to reproduce this on my end, so a reader of this blog who sent me a binary file to reproduce it.
Well, I was really scared to try that ‘killer’ file on my board, but well, that board is not that expensive, and I have 5 pieces of silicon at hand from a sample order :-). So I took some risk, and programmed that binary using the simple flash programmer. And indeed, when I wanted to debug it again, I got that dialog with my black Freedom board:
Device is Secure. Erase to unsecure?
I had pre-ordered some FRDM-KL25Z boards, and they came with the extra headers in plastic bags (see this post):
Pre-ordered Freedom board with headers
I have received as well a batch of the production boards, and for these I need to order the missing parts. So for everyone else, here are the Farnell part numbers:
Sometimes I show to much in a tutorial: only writing something to the UART? Sounds boring, so why not adding tasks, LEDs and a full shell implementation to the mix as in this post? Yes, definitely too much to start with at the beginning :-(. So less is more, and if it is just about the UART. And I promise: it is doable with around 50 lines of application code :shock:.
AND: I admit, this post title is a trap ;-). It is not about printf(). But it *is* about using the UART on the KL25Z Freedom board and to do things like printf(), and even more. Trust me. It is about how to write *and* read from the UART. While I’m using here the Kinetis-L ARM Cortex-M0+ KL25Z Freedom board, it is applicable to any other Kinetis device.
MCU on Eclipse 