This is my trial to rewrite from scratch the firmware for the 6-position switch controller on the RadioMaster TX16S breakout board.
Why such an endeavor, you might ask? By experimenting with DragonLink transmitter nearby, the chicken feet, incl. the 6 position switch output, stopped suddenly working on my RadioMaster TX16S. On further inspection, I was able to identify the SiLabs C8051F330 microcontroller on the breakout board, where the 6-pos. switches and LEDs are located, to be the central part of this functionality. Right next to the microcontroller is a 3-pin C2 debug header. When connecting SiLabs 8-bit Debug Adapter to it, the chip answered, so was alive. Why, the code did not run anymore although, remains a mystery, as the chip was powered correctly, and as it turned out in a later testing, was in good condition. Anyhow, as the original flash was code protected, I was unable to read it out, in order to e.g. try to run it in debug mode to see where the problem was. Without any source, I erased the chip and started this project.
If you wonder if I contacted RadioMaster Support and asked for a source - I sure did, but what I got back is a peculiar answer: Sorry we are unable to provide that information sir, may need to consult the manufacturer of the chip. Why on earth I need to contact SiLabs for the source code of the µC in RadioMaster product... makes absolutely no sense to me.
Do note that the 6-position switch firmware does not have much to do with the OpenTX firmware (<- code that is running on the TX16S main STM32F429BI microcontroller). The 6-position switch is handled by the dedicated C8051F330 µC on the breakout board and connected to the main STM32 µC only via a single wire - and over this wire analog voltage is transferred - the same way as sticks, sliders and pots do. C8051F330 has a DAC (digital-to-analog converter) that is used to generate the analog voltage.
My goal was to match the original functionality as good as possible, incl. the start-up Knight-Rider LED animation, as well as to match the raw value outputs of the position switches to the radio's main controller. I am pretty happy with the end result, but am open to improvement suggestions.
I started by locating the I/O configuration of the chip by tracing the tracks on the PCB:
- P0.0 - internal VRef, connection to capacitor
- P0.1 - analog out to main RadioMaster TX16S microcontroller (STM32F429BI)
- P0.2 - unused
- P0.3 - unused
- P0.4 - Position 6 Switch (rightmost), switched to GND
- P0.5 - Position 5 Switch
- P0.6 - Position 4 Switch
- P0.7 - Position 3 Switch
- P1.0 - Position 2 Switch
- P1.1 - Position 1 Switch (leftmost)
- P1.2 - Position 6 LED anode
- P1.3 - Position 5 LED anode
- P1.4 - Position 4 LED anode
- P1.5 - Position 3 LED anode
- P1.6 - Position 2 LED anode
- P1.7 - Position 1 LED anode
- P2.0 - C2 Debug data
- C2CK - C2 Debug clock
I used SiLabs Configuration Wizard 2 to generate the initial settings. The coding I carried out in SiLabs Simplicity Studio v4, using the Keil V51 v9.60 C-compiler. For integrating Keil 8051 Tools in Simplicity Studio, please see the Applicaton Note 104 by Silicon Labs.
For own compiling, you only need to fetch and import into Simplicity Studio v4 the file TX16S-6POS.sls (use menu File -> Import). It includes all necessary files for setting up the project for building and debugging.
In the repository you will additionally find for reference only:
- TX16S-6POS.hex - pre-compiled binary for direct flashing
- main.c - the source file for easy access without having to first go through the project import process in Simplicity Studio v4
- Config2.cwg - SiLabs Configuration Wizard 2 file
Project discussion in RC Groups forum blog post: