[Rock-dev] Proposal: NDLCom and Rock

[Martin Zenzes]

Hi,

looks like I got the task of implementing a general approach to 
connecting Rock and NDLCom. So now
I am searching for advise, comments and corrections.

Ok, let's start *lotoftext*:

Some piece of code should allow Rock-based "High-Level" software to 
speak in a generalized way with NDLCom-based "Low-Level" devices. These 
are, for example:
- FPGA (Spartan3/6)
- Bare metal Microcontroller (STM32, Atmega)
- µC Linux based Microcontroller (Blackfin)

Such devices use a simple byte-stream based communication. 
Message-length is crucial to keep buffer size limited. No attention is 
paid to things such as Endianess or Compiler alignments. It just works 
(tm) in the Moment ;-)

== Use-case ==

The intended first use-case would be to
- Coordinate lowest-level NDLCom-devices of the Sherpa1/2 (and Charlie) 
robots
- All NDLCom-devices should be supported
- Legacy support of the old iStruct Gui

The general Rock-approach seems to implement as much as possible in 
independent librarys, only providing the necessary glue-code in an 
orogen-Task specification. Right?

== ndlcom::Communication ==

Therefore, I would propose the cpp-library "ndlcom::Communication" to 
have the following properties:

- Open more than one "file descriptor" to read and write encoded NDLCom 
Messages as serial data
   - `/dev/ttyUSB0` - profane tty
   - `$IP:port` -- TCP/UDP connections
   - `/dev/can0` -- No CAN in Sherpa, but others use this already
   - `/dev/ndlcom0` -- Custom kernel device from !GumBridge FPGA, 
providing parsed and decoded messages
- Provide received Messages which are directed to the own receiverId as 
`ndlcom::Message` at the `readMessage()` function to a caller
- Accept `ndlcom::Message` at the `writeMessage()` function to be sent 
to the correct hardware interface

- Forward messages not directed at the own deviceId to the correct 
hardware interface
- Handle broadcasts: resend the message on all other hardware interfaces
- Mirror all received and transmitted `ndlcom::Message` as encoded raw 
NDLCom datastream via UDP. This would allow working with an unchanged 
iStruct Gui. This is transitory, for legacy support of the iStruct 
stack. Also easy access of all NDLCom-data without additional rock-code
- Statistics (bandwidth per interface, known devices, broken+missed packets)

See also the attached ASCII art...

=== iodrivers_base ===

The big question: Using `driver/iodrivers_base` makes things much 
simpler, but adds a dependency to the Rock CMake macros. As far as I am 
concerned this is ok.

There are some complex features in this library...

== Tests and Questions to the finished library ==

- How many NDLCom-Messages (~100byte) can be handled on a Gumstix?
- Routing, Broadcast...
- Write text about typical development-cycle for the lazy guys

== Rock Task ==

So, after *lotoftext*: This cpp-library is finally to be embedded in a 
Rock-Task, providing the appropriate Rock-Ports and executing the needed 
Hooks. Everything else, mapping certain NDLCom-Payload to certain 
Rock-Types or providing services based on NDLCom Messages, is done by 
other Rock-Tasks.




Greetings
     Martin

-- 
   M.Sc. Martin Zenzes
   Space Robotics

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