Backchannel UART without the UART

Anyone who has worked with a microcontroller is familiar with using printf as a makeshift debugger. This method is called tracing and it comes with the limitation that it uses up a UART peripheral. Believe it or not, there are 8051 variants out there that come with only one serial block and you are out of luck if your application needs it to communicate with another device.

[Jay Carlson] has a method by which he can piggyback these trace messages over an on-chip debugger. Though the newer ARM Cortex-M software debugger already has this facility but [Jay Carlson]’s hack is designed to work with the SiLabs EFM8 controllers. The idea is to write these debug messages to a predefined location in the RAM which the debugger can access anyway. His application polls a certain area of the memory and when it finds valid information, it reads the data and spits it out into a dedicated window. It’s using the debugger as a makeshift printf!

[Jay Carlson] used slab8051.dll interface and put together a C# program and GUI that works alongside the SiLab’s IDE. The code is available on GitHub for you to check out if you are working the EFM8 and need a helping hand. The idea is quite simple and can be ported to other controllers in a multitude of ways like the MSP430 perhaps. For those of you who like the Teensy, you might want to take a look at adding debugger support to the Teensy 3.5/3.6.

Filed under: Microcontrollers

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