Considered

• CAN
• SERCOS
• EtherCat

CAN

• Easy to implement and debug
• Messages have priorities
• Unknown delay until a message is transmitted
• Low speed
• Needs transceiver chips
• The bus is non-trivial to build

Sercos

• Bus with hard RT properties
• Inherent cycles for setting/getting data from slaves
• Very short delay between cycles possible
• Harder to configure
• No viable master implementation found
• There is only a basic API with no HW support

EtherCat

• Properties like Sercos
• Master: http://www.etherlab.org/en/ethercat/index.php
• Works with or without (slower) RT_PREEMPT patch for Linux
  • It should be manageable to get RT_PREEMPT working
• The master control process can be implemented using a C API

Proposal

• Implement a quick-and-dirty CAN bus so sensors and actuators can be steered
• When CAN works on a basic level try to set up basic EtherCat master/slave communication
  • Let the master talk to a proprietary slave
  • When the master works, try to set up a slave on a BeagleBone Black
• Implement the EtherCat control process

TODO: Decide on a deadline for basic EtherCat operations. It it's not working by then, improve the CAN bus