Wednesday, April 11, 2012

Custom designing monitoring hardware

I don't know how much use this will be, but...

Current project, and probably one of the definitely more interesting ones! I get to take an atmel atmega chip, and design a monitoring system around it. Considering the price of the chip, and how easily I can get boards made (I've got a stack of custom mistakes just sitting around waiting for me to figure out what to do with them), I decided to go the route of making my own arduino compatible board (note, only compatible... it's not technically an arduino).

First task I've gotten working is monitoring temperature, power, and lock status. So far so good. Then I found the Agentuino library... which is interesting to say the least. At the moment, it only really implements two functions, namely snmp_get and snmp_set. I'll be trying to get snmp_get_next working, which would probably end up being followed by snmp_get_bulk.

Why does this even matter? Well, this system is network attached for one thing. Currently it drops it's data via a post to a LAMP server- a simple php script picks up the data and stuffs it into a mysql db. pretty simple stuff. and it does it in less than 10K of rom space. I wish I could say the same for the snmp version, as it loads out at a minimum of 14K so far. I know most people are used to working in the megs and gigs realm of storage, but I started programming on systems that had less than 16K of ram, and stored their data on tapes... I find that reducing/optimizing code to fit in the smallest of space to be an almost elegant art form. And yes, I always hear that old obi-wan quote about "An elegant weapon, for a more civilized age" whenever I think about coding for space. I would've liked to have said I would be reducing the footprint further, but with having to add roughly 30 OIDs I don't think that's going to happen.

Considering I've got about 30K of space to work with, I'm hopeful to just get that far. Adding in the fact that I'm more than likely going to have to get at least get snmp_get_next working, I may have to opt for a far bigger chip than the atmega 328. I've seen some based on the atmega2560, which has about 256K of rom, versus the 32K I'm using now. I'll have to check out the price difference as well, but I don't think it will be enough to worry about. That alone should get me a hell of a lot more space for adding in new features.

As far as why I need to get snmp_get_next working? snmpwalk and most automated NSMs require snmp_get_next in order to walk to the MIB tree. For those of you who don't know, the MIB (Management Information Base) is a specific set of data points to be returned by the device in question. Considering how many MIBs there are right now, and the fact that anyone who puts snmp support in a device tailors their own, that's a lot of MIBs in this world. And they all work off of OIDs (Object IDentifiers). The OIDs let you request specific data, and the MIB tells you how to read that data. pretty simple, right? Well, like anything out there, it's been made convoluted enough to give me a headache.  There's a lot more information on the wiki about this, and described far better than I can.

Suffice it to say, I'm busy once again.

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