Manchester Code Proxy

Introduction

Manchester Code Proxy or MCP is an USB device with two USB endpoints:

• CDC - USB CDC communications device class can be used to emulate a serial port providing a virtualCOM port UART interface.
• MSC - USB MSC mass storage device class that makes a USB device accessible to a host computing device and enables file transfers between the host and the USB device.

On other side of proxy there is a single wire data interface. It uses a 3-state digital pin which works in bidirectional mode. The data is encoded using Manchester code. The following Manchester coding conventions are supported:

• IEEE802.3
• IEEE802.4
• G.E. Thomas

Getting started

For current list of issues see ISSUES.md. For list of serial console commands refer to COMMANDS.md. For hardware connection refer to WIRING.md.

Prerequisites

• STM32CubeIDE
• Development board STM32F411E-DISCO
• anyCS sensor

Importing project

1. Choose File -> Import...
2. In Import window select General -> Existing Projects into Workspace, click Next
3. Choose Select root directory then click on Browse... button
4. Navigate to downloaded project folder and click Open
5. In Projects: text box select mcp project
6. Make sure that Option Copy projects into workspace is checked, too
7. Click Finish

Refreshing index for code highlighting and browsing

After importing the project mcp should appear in Project Explorer window.

Right click on project name and execute the following options:

1. Refresh
2. Index -> Rebuild
3. Index -> Freshen all files

These commands will rebuild Eclipse indexer which would make code highlighting and code browsing.

Building

Right click on project name and execute Build project.

When the project building is done you should get something like the following:

Finished building target: mcp.elf
 
arm-none-eabi-objdump -h -S  mcp.elf  > "mcp.list"
arm-none-eabi-objcopy  -O binary  mcp.elf  "mcp.bin"
arm-none-eabi-size   mcp.elf 
   text	   data	    bss	    dec	    hex	filename
  22664	    520	  42368	  65552	  10010	mcp.elf
Finished building: default.size.stdout
 
Finished building: mcp.bin
 
Finished building: mcp.list

Debugging

1. In the menu click Run -> Debug configuration....
2. In new window double click on STM32 Cortex-M C/C++ Application. This will create a new item which has appeared just below STM32 Cortex-M C/C++ Application called mcp Debug.
3. Click on Debug button. The ST-LINK LED should start blinking on the board.
4. Click Run -> Resume to run the program.

Release process

When creating a new release go through the following steps:

1. Edit the version string APP_VERSION_STRING in application configuration file: configuration/config_application.h.
2. Edit the timestamp string APP_TIMESTAMP_STRING in application configuration file: configuration/config_application.h.
3. Create commit and push

Configuration

The application is currently configured during the compilation.

Communication speed

The application uses quarter of a bit period to generate the waveform. This setting is specified in file mdrv.c in data structure called g__default_config in structure membere quarter_period_us. The time is specified in us.

Clock stability and accuracy

This firmware uses High Speed External (HSE) oscillator clock as its main clock source. This clock is used to derive all peripheral clocks and software timeouts.

On the Discovery Kit board HSE oscillator is connected to X2 crystal. There is no information available which part numbers are used (Bill of Materials is not accessible on manufacturers site). The markings on the crystal are: 8.000s3Z. Unfortunately, information on crystal marking is also not available.

The only fact that is known about used crystal is that must fulfill the USB 2.0 specification for clock accuracy. The USB 2.0 specification states that for full-speed communications, the data rate is specified to be 12 Mbps +/- 0.25%.

This means, that the used crystal has at least +/- 0.25% accuracy. As for stability of the clock, no information is available.