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Zigbee/802.15.4 Chip Comparison Guide | Print |
Blog - Zigbee
Written by Akiba   
Tuesday, 18 March 2008

I put together a Zigbee/802.15.4 chip comparison guide. There is another one up on the web , but it hasn't been updated since 2004. I thought I would put together the 2008 version since a lot of the info on the 2004 chart is a bit obsolete. Such as:

  • The AT86RF210 is EOL'd
  • CompXS was purchased by Integrated
  • Ember's EM2420 was a re-marked CC2420 which disappeared after TI purchased Chipcon
  • ZMD no longer makes their Zigbee chip. I think they cut some deal with Renesas which gave them the IP
So I figured it was time for an update. I don't guarantee the accuracy of the tables, although I took all of the information from the datasheets on the vendors' websites. Also, I initially tried to do it in HTML tables, but HTML tables suck. So I put the tables together in an external program and then exported it as a JPG. Hopefully, you can read it. The first table is a comparison guide for transceivers only. You can click on it to get the full JPG. All values are "typical" unless stated otherwise. The font is a bit small due to the size of the table so I've included a PDF document at the end of the post in case it's difficult to read.

Zigbee Chip Comparison - Transceivers

The second comparison table is for integrated MCUs + Transceivers. The integrated category is quite complex and I might expand this one later.  Integrating an MCU and a radio is difficult because many features come into play: ADC, ADC Resolution, number of timers, types of timers, GPIO, development tools, architecture, etc... I might need to make a more comprehensive list, but here is the first stab at it. Regarding the power consumption values, in cases where a multi-chip module are used (they just stuck an MCU and a radio die on the same substrate), the power values are given as separate MCU and RF numbers since I couldn't get the actual total consumption value. If anyone can correct me on these, please let me know...

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Zigbee Buzzing - At Least According to Google | Print |
Blog - Misc
Written by Akiba   
Sunday, 16 March 2008

I have to say that the Zigbee Alliance marketing machine is doing a pretty good job. I stumbled across a little known service offered by Google (at least little known to me) called Google Trends . It's pretty interesting. It shows the amount of search volume for a particular keyword over time and it can be used to infer the popularity of a term. Here's an image of the Google Trend for Wikipedia spanning from about 2003 until now.

Wikipedia on Google Trends

It pretty much makes sense. There wasn't a lot of action going on until about 2005 when Wikipedia started really taking off. People started generating content, which in turn increased the traffic to the site, which in turn inspired other people to contribute to the content.

Well, my point isn't to show you the popularity of Wikipedia. I actually did a search for Zigbee and found something quite interesting. If you look closely, you can see that the number of searches is relatively constant over time, with a slight decrease over the past two years. That's not very impressive. However if you take a look underneath the trend, there's a figure that's interesting. It shows the number of news references for Zigbee over time is increasing. It was fairly flat from 2003 to 2006 with a couple of spikes, probably corresponding to significant press releases. By the way, the square with the 'A' in it marks the time when the first Zigbee spec was released.

Zigbee on Google Trends

If you look at the trend from 2007, you can see that the news references get much busier. This means that Zigbee is showing up a lot more in the news. This could mean that the Zigbee Alliance is issuing more press releases, but normally, this has the effect of numbing the publications to the releases so that fewer get picked up. In my un-expert and un-professional opinion, this probably means that more companies are either releasing Zigbee products or are announcing that they will be adopting the technology in one form or another. I guess it could also mean that more companies are getting frustrated with it, but let's hope that's not the case. Hmmm...Not bad, Zigbee Alliance!

The trend pretty much follows in the footsteps of Bluetooth which formed the Bluetooth SIG in 1998 and didn't really catch on until about 2005 or 2006. I think it's about that time when I started noticing people seemingly talking to themselves with only a big-ass earbud in their ear and no wires hanging out. I also checked for Bluetooth on Google Trends, but unfortunately, it looks like their data only goes back to 2003. The search volume at that time was also fairly constant already, but if you look at the news references, it starts getting busier around 2006. Here's the chart:

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Sony Bravia LCD TVs Using Zigbee for Remote Control | Print |
Blog - News
Written by Akiba   
Saturday, 15 March 2008

I posted previously that I was hoping that Zigbee would be incorporated by Sony in their LCD TVs. Little did I know that I was psychic. The Nikkei just released an article about Zigbee forecasts and in it, they mentioned that

" ZigBee was employed as an infrared substitute for the RF remote controller of Sony's "BRAVIA" LCD TV in 2007."

 Nice!

 

 
Dev Journal - Implementing the APS Data Service | Print |
Blog - FreakZ
Written by Akiba   
Saturday, 15 March 2008
The APS layer, also known as the application sublayer, is the top of the main data path in a Zigbee stack. Th only things that lie above it are application objects, which are implementation specific. The APS layer handles data transmission and reception as well as table management. The main tables that are located in the APS layer are: binding, discovery cache, address map, and endpoint grouping tables. We'll discuss the tables later on when they get implemented. Right now, I'd just like to focus on reliable and unreliable data transmission.

The APS data service is the main vehicle for device discovery and management. The application objects use this service to communicate descriptors to each other, handle client/server communications, and perform remote management and provisioning. The data path for this layer can get a bit complicated due to the many options available for transmission and reception. The binding, grouping, and address tables are all used when building the frames. However on a fundamental level, there are only two types of transmissions: reliable and unreliable. Reliable transmission is transmission which requires an APS level acknowledgement from the destination device. Unreliable transmission is when you just send it out and you don't care if it arrives or not.

The IEEE 802.15.4 spec already implements a form of acknowledgement, but this is a PHY layer acknowledgement. Since most 802.15.4 radios implement the ACK in hardware, the 802.15.4 ACK just says that the frame was received into the chip's FIFO properly. The APS level ACK says that the frame was processed correctly as well, which is very important. Many things could go wrong from the PHY to the APS layer. Some examples of dropping a frame between the PHY and the APS processing are:

1)    The received frame requires routing, but no route can be found for it.
2)    The received frame goes to a router with no routing resources and no tree routing ability.
3)    The MAC doesn't pull the received frame out of the chip's FIFO quickly enough and it gets overwritten by another frame.

If a reliable transmission is needed, then an APS frame with the ACK required is probably the safest way to send it. However it also is costly in terms of performance.
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Circuit Cellar #211 - A Platform for Wireless Sensor Networks | Print |
Blog - News
Written by Akiba   
Friday, 14 March 2008

I'm pretty slow on my magazine reading from the states since I have to wait for my mom to send me a care package of some of my requested magazines and American goods. She normally purchases them when she has a chance and stockpiles them until she can make one large shipment to me. I figure that on average, I'm about 2-3 months behind on my magazine reading.

So I was suprised when I picked up Issue #211 of Circuit Cellar . It's an excellent issue for me with two very relevant articles to what I am doing now. One of them is a very good article on wireless sensor network platforms. The other is an article on the basics of antenna simulation. Both of which I am interested in.

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Zigbee Gossip - Don't Take My Word For It | Print |
Blog - News
Written by Akiba   
Friday, 14 March 2008

Well, yesterday I was out all day running errands and one of them took me to the Immigration office in Tokyo. I don't like going there because it's like the DMV (Department of Motor Vehicles) in the US. It's basically a time sink, where once you enter, you have to plan on spending at least two hours of your time waiting. However one good thing came out of it.

One of the local chip distributors in Tokyo is located along the way to the immigration office so I got a chance to meet up with them. One reason I like to hang out with distis is that they always have interesting news since they have to visit so many companies all the time. They're the ones that are usually plugged in on trends and know what's popular among the electronics industry. So after meeting the local disti, I got some interesting news (gossip) about Zigbee usage at some Japanese companies.

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Down and Out - Pollen Sucks | Print |
Blog - Misc
Written by Akiba   
Thursday, 13 March 2008
I normally try to update my blog everyday. However I'm getting killed by the pollen levels in Tokyo . It feels like I'm getting hit by a mutant form of the common cold. I'm just going to curl up with a beer and watch Entourage on the internet.
 
Microsoft Sensor Modules - Rough Cost Breakdown | Print |
Blog - Misc
Written by Akiba   
Tuesday, 11 March 2008

The Wireless Sensor Networks Blog just posted an interesting link to an article at Popular Science . Microsoft unveiled a prototype sensor module reference design at Microsoft TechFest that they are currently using to monitor the temperature from their server hardware. I can only assume that it came from Microsoft's Networked Embedded Computing division at the Microsoft Research Labs. Well, I have nothing against Microsoft, and in fact, I enjoy using Windows (XP, not Vista). However the article does claim that the sensor modules are cheap, so I thought I would give a best guess-timate of how much the reference hardware bill of materials cost.

Luckily, the article provides an excellent clue when they said that they are using a TI transceiver that costs about $3. Well, that sounds exactly like the good ol' TI (Chipcon) CC2420. Why not the CC2520 you ask? Well, the CC2520 was just released recently (see my review of that chip ) and I am assuming that for them to make the PCB, write the software, create a nice plastic enclosure, and already have it running in their server rooms, the project must be more than a few months old. Hence, I am going with my initial assumption that they are using the CC2420.

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Yet Another Article Claiming that C Programming is Dying | Print |
Blog - Embedded
Written by Akiba   
Tuesday, 11 March 2008

Man, if I had a dollar for every article I read that claims C as a dying skill, I'd probably have around five dollars by now. Hmmm...that would include assembly language programming, I think. Well, here's another one, where C made the top 10 dying skills list at ComputerWorld . The article is a bit old, but C ranked just below cc:Mail programming in the list. With C programming as the second most popular language in the world ,  why is it that people think of C as a dying language?

That's an interesting question. I think it's probably because it's not really taught in universities anymore, since they are focusing on scripting/interpreted languages .  The reason behind that is that C is a difficult language to understand, especially for undergraduates. Having college students track down memory leaks and pointer problems is an easy way to make them cry, and kind of mean too. As Wikipedia put it: "...the safe, effective use of C requires more programmer skill, experience, effort, and attention to detail than is required for some other programming languages" . With the tech companies in the US shouting at politicians and universities that they aren't turning out enough computer science engineers, the schools seem to be watering down the curriculum to make sure that less people drop out. Is it bad? Is it good?

In general, I don't think its bad. Having more Java and Python programmers in the world can't hurt. You can do a lot of interesting things with those languages and make many useful applications; like say Google, where Python is one of the official languages. However I can say that it's bad for the future of the embedded industry. Anybody in the semiconductor or electrical engineering industry today knows that there is a shortage of embedded engineers . One of the main reasons for this shortage is that C is rarely taught anymore. Even C++ is slowly getting faded out from the curriculum at many schools. And in the embedded realm, C is king. 

At the semiconductor startups that I've worked at previously, software drivers are the main difference between being able to sell a chip or not. That translates into revenue for the company. Having software drivers available enabled a former startup company I worked at to generate $10M+ in sales off of one chip. Not having software drivers available also forced the company into bankruptcy. Well, that and a couple other factors. The reason why software couldn't be finished in time and fit the customer requirements was that its hard to find good embedded software engineers. These days, IC design is mostly stitching together different IP cores and running tests at the toplevel. But that level of design automation and reuse has not hit software yet so it's still largely a craftsman-based skill. Unfortunately, the available pool of craftsmen is shrinking because there are fewer places to learn the language, and nobody wants to give on-the-job training to a noob that, with one wrong pointer operation, can bring a whole system to its knees. 

So the main point of my post, which I seemingly forgot, is that C is still very much needed and anything but a dying language in this industry (embedded). And the benefit of knowing it often comes in the form of a six-figure salary; at least if you find the right company. Laughing

 
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