"otter" is for "OpenTag TERminal." It is a POSIX-C app that provides a client-side terminal shell for communication between a TTY device (typically a PC) and a binary target (typically an embedded device). The implemented binary packet protocol is called MPipe, which is released with OpenTag. It is similar in nature to projects like Bitlash and Pinnoc.io in that it is a client-side shell, but it differs because it is for OpenTag, and OpenTag has a much more powerful, extensible, and generic data language than any of these projects have. This also means that OpenTag is harder to use, but I'm making Otter to fix that.
Otter is presently in Beta.
The only external dependecies are listed below. talloc and libbsd are easy to download via most package managers. musl libfts is harder to get, but it's only needed for some very specific platforms.
- talloc
- libbsd (obviously not needed if your platform is a BSD)
- musl libfts (source, openwrt pkg), which is only needed on linuxes using the musl libraries.
otter is part of the HB Distribution, so the easiest way to build it is via this distribution.
- Install external dependencies.
- Clone/Download hbdist repository, and
cdinto it. - Do the normal:
make all; sudo make install - Everything will be installed into a
/opt/directory tree. Make sure your$PATHhas/opt/binin it.
If you want to build otter outside of the HB Distribution, you'll need to clone/download the following repositories. You should have all these repo directories stored flat inside a root directory.
- _hbsys
- argtable
- bintex
- cJSON
- clithread
- cmdtab
- hbutils
- libotfs
- otvar
- OTEAX
From this point:
$ cd otter
$ make pkg
You can find the binary inside otter/bin/
Otter is a terminal shell that operates on a POSIX command line, between a TTY client/host and a binary MPipe target/server. It implements a human-interface shell for many of the M2DEF-based protocols used by OpenTag, although it is different than a normal terminal shell because all of the translation between the binary interface and the human interface takes place on the client (i.e. the otter app) rather than the server.
Usage of Otter could be compared to usage of the standard, command line version of FTP (ftp).
Otter is implemented entirely in POSIX Standard C99. It is a multi-threaded app, making use of the PThreads library to do the threading. It has no dependencies other than Bintex and M2DEF, and these are shipped as source with Otter (you can optionally build it with Bintex and M2DEF libraries).
Versions 0.1 to 1.0 will use only the normal POSIX command line interface (stdin, stdout). More features of M2DEF will be introduced gradually, and more advanced shell features will be introduced gradually. Future versions (after 1.0) will introduce NCurses UI, and potentially also a shell interpreter for NDEF (although this really depends on the prevalance of NDEF libraries in the open source domain).
MPipe is the wrapper protocol that Otter and the target must use to transport packets of data. It is simple enough that any embedded target able to print over a canonical TTY should also be sufficient to use MPipe. The packet structure of MPipe is shown below:
Byte 0:1 -> Sync (FF55) Byte 2:3 -> CRC-16 Byte 4:5 -> Payload Length Byte 6 -> Session Number Byte 7 -> Control Field Byte 8:- -> Payload
The MPipe header is 8 bytes, and it may be extended in the future via the Control Field. All values are big-endian. The CRC-16 is calculated from Byte 4 to the end of the packet.
Depending on the value of the Control Field, the Payload can be arbitrary data, an M2DEF message (used by OpenTag), or an NDEF message (used by NFC). M2DEF was previously called "ALP," but it is now officially called M2DEF in order to highlight the large degree of compatibility it has with NDEF.
More information on MPipe is covered in official MPipe documentation. http://www.indigresso.com/wiki/doku.php?id=opentag:otlib:mpipe