Using newlib with Stellaris Launchpad

using-newlibc-with-stellaris-launchpad

[Brandon] is taking us further down the rabbit hole by demonstrating how to use newlib with the TI Stellaris Launchpad. This is a nice continuation of the framework he built with his post about using GCC with ARM hardware. But it is most certainly one level of complexity deeper than that initial article.

Using newlib instead of glibc offers the option of compiling C code that includes system calls common when coding for computers but which are rare in embedded systems. Using something like printf is generally avoided because of the overhead associated with it. But these processors are getting so fast and have so much RAM that it may be useful in certain cases. We briefly thought about implementing malloc for creating a linked list when working on our STM32 snake game. [Brandon's] work here makes the use of that command possible.

The process starts by adding labels for the beginning and end of the stack/heap. This makes it possible for functions to allocate memory. After taking care of the linker script changes you must implement a few system call functions like _sbrk.

Using printf-style output to debug Arduino

First off, if you’re looking at that title and thinking it’s flame-bait, please hold off. What [Ihsan Kehribar] is working with is another way to get some feedback for what’s going on with your Arduino project. Or really any AVR project that uses an ISP connection. He’s added text output for AVR programs similar to the printf function used for a lot of non-embedded C development.

So, we’d bet you’re asking yourself why he’s not just using outright debugging? The AVR line supports many different types of it. But that can be complicated, and usually requires a proper programmer. If you just want to watch to see what values are changing, and when functions are being executed, this isn’t a bad solution. He uses the computer to continually poll the chip. Whenever the sketch calls the his print library it answers back with the payload to be displayed in the terminal. The overhead shouldn’t be too high, and if you’re smart about it this can be flagged as a debug option at the top of the program file.