Sunday, April 30, 2006

Unforgettable Day: Sydney Buses

Yesterday, i lost my wallet in the bus. Yup, it was my fault, i dropped it. Stupid me, hay?

(continued 3 May 2006)
Here's the story. It was a sunny warm saturday. Agung asked me to go out to city with Amy (or is it Ami, or Amik? whatever). As it was quite hot that afternoon, we decided to take an air-conditioned bus instead of the old buses without one. So, after 10 minutes of waiting or so, a 396 bus heading for Circular Quay arrived at the UNSW bus stop we were waiting at.

Bus tickets aren't cheap here in Sydney. That's why Agung tried to show his student card to the driver, hoping that he will get a concession (50% discount). But he failed... the driver knows too much haha. Now here comes the part where trouble comes. Agung wanted to look at my student card which has a concession label on it, a circle with some words like NSW rail.... something like that. I pulled my wallet out of my pocket, and showed my student card to him. The next thing that happened was, after he took a look at my card, i returned it back to my wallet, BUT... i didn't put the wallet back to my pocket. I was too lazy to do it, i guess. Instead, i put it on top of my bag which i put on top of my lap.

(to be continued again hihi)
Wednesday, April 26, 2006

Perjalanan ke Queensland: NSW bagian utara

Matahari terbit gak lama sesudah kami meninggalkan kota Grafton NSW:

Pajero nya Akbar, sedang disalip truk:

Sebuah toko dengan udang raksasa haha

Sungai berkabut, sekitar setengah jam sesudah beranjak dari Grafton

Ladang tebu, serasa di Klaten huaha :p

Thursday, April 20, 2006

Sunset at Kensington

Easter holiday kemarin, seperti yang bapak2 ibu sodara2 sekalian barangkali sudah ketahui, anak2 Day Ave berlibur ke Queensland!!! (Gold Coast itu di Queensland, utara Sydney, btw...)

But... tapi... sebelum foto2 Gold Coast ku-upload seperti permintaan Lissya, foto kampung sendiri di sore hari sebelum berangkat akan kupampang di sini karena lumayan keren menurutzku...

It was such a beautiful evening that day at Kensington, although it rained a bit the afternoon before..

This is a view from the window of my room, facing towards my Uni. (Samuels building can be seen in the far background)

This is the backyard of my flat.

There was an wonderful rainbow that evening...

And the sky was marvelous...

Wednesday, April 12, 2006

Stupid thesis? Think again...

Just when i thought my research topic was so boring, i came up with this claim:

"Interconnect research is harder but has greater potential returns."

(William J. Dally, 2002, Computer architecture is all about interconnect,, accessed 11 April 2006)

Okay, now back to work :)
Tuesday, April 11, 2006

Low Power Interconnects: Literature review early draft

Comments, suggestions, and questions are most welcome...


Technology scaling in integrated circuits allows an increase in operating frequency as well as transistor count per die area. To a certain extent it also reduces power dissipation due to lower supply voltage. The benefits obtained from scaling power supply voltage and threshold voltage had been discussed in [1] and [2], where delay reduction as well as power savings can be achieved. However, further scaling down threshold voltage will eventually cause subthreshold leakage current to increase exponentially with threshold voltage reduction. [3]

One other major obstacle in technology scaling is the increasingly larger delay and power consumption caused by the on-chip interconnects compared to gate delay and power dissipation. [4] explains that interconnect delay is a critical factor that limits circuit performance as they do not decrease as the gate delay scales down. Due to higher circuit complexity, total length of on-chip interconnects will increase, hence delay, power consumption, and reliability will become worse. This study will review current low power buses schemes, which includes low voltage swing buses and coding for minimizing power, as well as investigating the possibility to combine these methods with an error detecting mechanism to allow adaptive voltage swing buses.

This chapter will first discuss the modeling of interconnects, and then several optimal interconnect design techniques are reviewed, namely repeater insertion, low swing buses, coding techniques, and error detection mechanisms.

Interconnect modeling

A distributed RC model of a transmission line would be the accurate modeling of a single interconnect wire. However they are complex, hence the more simple RC network are normally employed. [5] Interconnects modeled as RC π3 structures are used in [6]. In [4], interconnects are treated as RC trees modeled as L or π-type circuits.

The effect of crosstalk between neighboring lines on interconnect delay is modeled by including a coupling capacitance parameter between adjacent lines in a bus. A discussion of the consequence of crosstalk to delay performance is discussed in [5], where a delay variation of 500% is possible due to Miller effect on neighboring lines where logic transition occurs. As can be seen from the ITRS 2003, the feature size and minimum pitch dimension decreases with technology scaling. [7] This implies that crosstalk would have a larger impact on interconnect delay in the future.

The derivation of coupling capacitance between conductors can be done using the publicly available 3D field extraction software such as Fastcap which had been used in [4].

Repeater insertion

Repeaters are placed in long interconnect wires in order to reduce the interconnect delay, where the quadratic relation between delay and wire length without repeaters becomes a near-linear relationship.[8], [5]

The problem with repeater insertion in the future is addressed in [9] and [8] where the number of repeaters required increases exponentially with technology scaling according to Rent's rule. [9] proposes an optimum repeater placement strategy considering power and delay trade-off.

Another method to reduce power of interconnects with repeaters is proposed by [10], where coding is employed to the bus in order to minimize crosstalk effect on delay. This combination however, had been shown to actually reduce power and delay on the 90nm and newer technology nodes, whereas a power penalty is introduced by the coding circuitry for the 130 nm technology node.

Low-swing buses

A review of several low-swing bus techniques is described in [6], where some improvements are also proposed.

In terms of the voltage swing range, low voltage swing buses may be divided into two categories. The first type has a voltage swing around the midpoint (Vdd/2), and the second type swings from Vss towards a low Vdd. [6] reviewed several low-swing on-chip interconnects particularly from the first type. These includes static drivers as well as dynamic driver circuits. In this paper, the authors also proposed improvements over the reviewed low swing buses in terms of signal-to-noise ratio. Among the methods reviewed, the differential technique seemed to have the most energy-delay savings compared to the others, despite its lower SNR and double driver and wire requirements.

In [11], an improvement was introduced over one category from [6], namely the dynamic diode-connected driver which has a voltage swing around midpoint. A preliminary simulation on 0.18um technology using Cadence shows that this technique reduces energy-delay by 32.13% compared to the full swing CMOS interconnect. However, this design has a lower signal-to-noise ratio compared to the full swing CMOS buses. [12] proposed a different interconnect design which has a voltage swing from Vss.

Coding techniques

Simple coding schemes are normally employed on buses to reduce the effect of crosstalk. This had been done in [7, 10, 13 , 14]. The main objectives of these techniques is to avoid opposite transitions in adjacent lines.

Coding had also been used for error protection for buses in [15]. In the paper, a simple parity check for error and a double and triple error correction using Hamming codes were used.


[1] R. Gonzalez, B. M. Gordon, and M. A. Horowitz, "Supply and threshold voltage scaling for low power CMOS," Solid-State Circuits, IEEE Journal of, vol. 32, pp. 1210-1216, 1997.

[2] A. P. Chandrakasan and R. W. Brodersen, "Minimizing power consumption in digital CMOS circuits," Proceedings of the IEEE, vol. 83, pp. 498-523, 1995.

[3] J. T. Kao and A. P. Chandrakasan, "Dual-threshold voltage techniques for low-power digital circuits," Solid-State Circuits, IEEE Journal of, vol. 35, pp. 1009-1018, 2000.

[4] J. Cong, P. Zhigang, H. Lei, K. Cheng-Kok, and K. Kei-Yong, "Interconnect design for deep submicron ICs," 1997.

[5] J. M. Rabaey, A. P. Chandrakasan, and B. Nikolic, Digital integrated circuits : a design perspective, 2nd ed. Upper Saddle River, NJ: Prentice Hall, Pearson Education International, 2003.

[6] H. Zhang, V. George, and J. M. Rabaey, "Low-swing on-chip signaling techniques: effectiveness and robustness," Very Large Scale Integration (VLSI) Systems, IEEE Transactions on, vol. 8, pp. 264-272, 2000.

[7] S. R. Sridhara, N. R. Shanbhag, and G. Balamurugan, "Joint equalization and coding for on-chip bus communication," 2005.

[8] A. Maheshwari and W. Burleson, "Differential current-sensing for on-chip interconnects," Very Large Scale Integration (VLSI) Systems, IEEE Transactions on, vol. 12, pp. 1321-1329, 2004.

[9] P. Kapur, G. Chandra, and K. C. Saraswat, "Power estimation in global interconnects and its reduction using a novel repeater optimization methodology," 2002.

[10] S. R. Sridhara and N. R. Shanbhag, "A low-power bus design using joint repeater insertion and coding," 2005.

[11] M. Ferretti and P. A. Beerel, "Low swing signaling using a dynamic diode-connected driver," 2001.

[12] P. Caputa, M. A. Anders, C. Svensson, R. K. Krishnamurthy, and S. Borkar, "A low-swing single-ended L1 cache bus technique for sub-90nm technologies," 2004.

[13] H. Po-Tsang and H. Wei, "Low power encoding schemes for run-time on-chip bus," presented at IEEE Asia-Pacific Conference on Circuits and Systems, 2004.

[14] S. R. Sridhara, A. Ahmed, and N. R. Shanbhag, "Area and energy-efficient crosstalk avoidance codes for on-chip buses," 2004.

[15] L. Li, et al, "Adaptive Error Protection for Energy Efficiency," presented at Proceedings of the International Conference on Computer Aided Design (ICCAD'03), 2003.

Wednesday, April 05, 2006

5 essential research software tools

Whether you are doing a school project, or a final year thesis, you would normally use internet to find the information and resources you need. Once you get all the informations you think are important, then what?

It's a good idea to start a bit organized. You would need a plan. Okay, you don't need a software to write a plan. A piece of paper and an old dull pencil would be just the right stuff to start with. But however, using (1) Microsoft Word or OpenOffice Writer 2.0 won't cause you any harm either. Jot down anything you have in mind on a new fresh document. I know it's better to actually use a paper and pencil instead of a keyboard and a text editor, but because i am talking about software tools in this post, i'll suggest you to use them anyway :) Another obvious reason why i put these text editors as the number 1 research tool is that you would eventually need it to type your research report, sooner or later...

Now you have got a fair enough plan. What you do next would probably browse the internet for information and materials for your study or whatever research you are doing. My favorite way to start searching the Net is to type in a keyword of my problem to The next thing that would happen is that you ge thundreds, if not thousands of links to all potential sources of valuable information. Naturally, you would then open many of those links and save many of the articles to your harddrive for later viewing. Chances are, your folders would become a bit messy with hundreds of files you have downloaded. That's where (2) Google Desktop proves to be life-saving. This handy dandy program will index and be able to search any keywords within documents of any filetypes such as *.doc, *.pdf, *.xls, *.ps, *.html, etc in your computer. Say goodbye to "where did i put my file about ****" problem :) No matter how messy your file organisations are, retrieving your file back when you need them will no longer be a problem.

After sufficient amount of information had been collected, it is now time to sort out your informations and map them into a presentable format which is easier to remember. This kind of method is now popularly known as a Mindmap(r), proposed by Tony Buzan. Certainly you can always draw a mindmap yourself on a plain paper with colorful pencils or markers. But, yes... you can draw a mindmap on your computer if you wish. And you can do it fairly easily on your beloved computer using (3) Joerg Mueller's FreeMind Mindmap(r) software.

One other software that i find so useful is (4) EndNote version 9 which i got for free from my Uni. What it does is it manages all bibliographical information of the resources you collected and potentially use on your research or thesis. You can easily add entries to its database using standard bibliographical entry formats from journal databases such as ACM Portal, IEEExplore, ProQuest, etc. You can always type in a piece of reference source entry manually if you do not mind the hassles of doing so. So what's so special about EndNote? This program can automatically format the document you are typing so that it complies with any referencing style that you are supposed to use. For example, articles written for the IEEE normally cites another work using numbers in square brackets, and at the end of the paper, the reference list is also numbered in square brackets which are refered to in the text. If you wish to change this referencing style to APA for instance, all you need to do is tell EndNote to change the style. Another good thing about EndNote is that the references in your database can be represented as an anotated bibliography with the abstract of every articles included.

The last thing you need is (5) iTunes (the current version now is 6) haha. It is important, my dear friends! It can be awfully quiet inside your lab or room where you work in, and this quietness will definitely make you sleepy, and you don't want this to happen would you? If you enjoy music, listening to them while doing your research work would hopefuly be enjoyable as well :D And why choose iTunes instead of Winamp or WMP for instance? The reason is that in iTunes you will be able to search much easier, you can also share your music to other iTunes on your local network, you can open the music store easily, and you can download podcasts of your favourite radio shows for free.

That's all five software that i strongly suggest you to have in your computer for research purposes. And the good news is that all of them are FREE except Microsoft Word and EndNote. For Endnote, you must pay the license if you are not a student or staff at my uni haha. An alternative to EndNote is the open-source program called Bibus, but i still can't get the hang of it. Next time i'll probably try to post about 5 most important sites for research :)

(1) OpenOffice Writer 2.0
(2) Google Desktop *
(3) Joerg Mueller's FreeMind Mindmap(r) software
(4) EndNote version 9
(5) iTunes

* i had just recently been advised that there are some potential security issues concerning the usage of google desktop (GDS) on your computer. Vital informations from your computer may be read by unauthorised access through google desktop indexing share feature. Therefore i believe that turning on the encryption feature for google desktop's index file is a good thing to do, and activating your google desktop sharing feature would be rather dangerous -- try to avoid it. Nevertheless, i couldn't imagine working on my thesis without GDS. It is too important.