Understanding the hardware architecture of smartphones

With the development of smartphones, the devices began to incorporate more and more functions. The big problem is that more features mean more chips and more processing cycles, which means higher power consumption. Because batteries do not evolve at the same speed as the appetite of the manufacturers (and buyers) with new features, compact appliances and offer a good range of batteries has become an increasingly difficult task.

Just keep in mind that a cell with a Li-Ion 860 mAh battery offers just over 3 watts of energy (corresponding to an average laptop consumes only 5 minutes) to perform all its functions until the next refill ( to calculate the total energy stored by the battery, multiply the voltage in volts, the amperage in mAh. A battery of 850mAh and 3.7V, for example, stores a total of 3,219 milliwatts, or 3.219 watts). However, unlike what we have laptops, the autonomy of smartphones to be measured in days rather than hours. By then, you can get an idea of the size of a headache for designers.

On PC computers, are used x86 processors such as Core 2 Duo and Phenom. They are optimized for performance chips, including a brutal amount of transistors with large L2 caches, and dedicated units for decoding instruction scheduling, branch-prediction circuits and multiple execution units per core.To get an idea, a Core 2 Duo E8200 Penryn-based core (which is a relatively small chip by today's standards) has no less than 410 million transistors and has a typical consumption of 65 watts.

A maker of smartphones that are interested in using it, would find a way to put a cooler with 80 mm copper sink and a 6-cell battery inside the unit. Even if they did, he probably would not sell very well ...:)

That is why there has not smartphones based on x86 processors. Even low-power processors like the Atom, have an electrical load is too high for a smartphone, that the battery would last only one or two hours.

The restrictions regarding the size and consumption has made the hardware of smart phones evolve in a way quite different from the PC, using low-power processors and highly integrated chips.

The most notable change is the use of ARM processors rather than x86 chips. ARM chips are 32-bit RISC processors, which feature a highly optimized architecture, with few transistors and a power consumption extremely low.

Although not as well known nor commented on the Nehalem or Atom, ARM processors are produced in larger volumes and brutally used in all sorts of devices, routers and ADSL modems to video games, the Nintendo DS. Virtually any electronic you have at home that uses a 32 bit processor and is not a PC, using one or more ARM processors, including, of course, your smartphone.

Another secret is the integration of components and the use of dedicated controllers for different functions, different from what we have on a PC, where almost everything is done by the main processor. The advantage of using dedicated controllers is that they perform their functions directly in hardware, instead of performing a software intended to perform the same function. Thus, they can perform their tasks with fewer transistors and less processing cycles, which translates into a lower power consumption. Any smartphone now has several of these drivers, who are off most of the time and are awake only when they have some work to do.

We have here an OMAP2420 (manufactured by Texas Instruments), an example of "processor" intended for use in smartphones, which is used in many Nokia models, including the N95 and E90.

Like other similar chips, it is actually an SoC (system on a chip), that is, the combination of a CPU and several other components into a single chip, including an ARM11 processor, a DSP chip transmitters for frequency bands supported, and interfaces to various other components. If you're curious, here is a block diagram of the chip:

He also has a video accelerator, which helps in decoding various video formats, processing of captured images and videos using the camera (and other related functions) and also a dedicated 3D accelerator, which is triggered when you run games or other applications using 3D graphics. As the power consumption needs to be very low (unlike on a desktop, where the 3D card can consume 50 watts or more ...) performance is quite limited, only 2 megapixels (for comparison, a Voodoo 1 (the one launched by 3DFX in 1996) had a fill-rate of 50 megapixels).

Nevertheless, in the hands of competent developers, these two megapixels can yield much. There's even a version of Quake for S60 (http://koti.mbnet.fi/hinkka/), which is able to take advantage of the graphics accelerator:

Another example is the Qualcomm MSM7200, which is used in various devices from HTC and Toshiba, among them the HTC TyTN II and HTC Touch Dual.It is also based on an ARM11 processor, but includes a different set of auxiliary components. They include a video accelerator, which is responsible for video decoding in different formats (relieving the main processor and helping to reduce consumption), a 3D accelerator optimized for games and applications written in Java, an ARM9 processor helper to the signal processing of the 3G network and a Qualcomm chip gpsOne, a 20-channel GPS receiver:

This level of integration is needed to keep power consumption at acceptable levels and to reduce the manufacturing cost (as they produce a single chip containing multiple components is cheaper than making several separate chips) and reduce the size and weight of devices.

New features such as graphics accelerators and GPS chips begin their careers as separate chips, which increase the cost of handsets. This causes, they initially remain restricted only to the most expensive players. However, over time, chip makers like Texas Instruments and Qualcomm are offering integrated solutions with them, which reduces costs and allows them to pass to be used in even the simplest devices, as is currently happening with GPS chips.

Naturally, the more components working simultaneously also means a higher power consumption. A major problem with the current generation of devices is the poor battery life when using a 3G network.

On most devices, the battery lasts no more than two hours in situations where the device is continuously transmitting data, such as when using your smartphone as a modem and download an iso file, for example. To a lesser degree, this also applies to applications that transmit a considerable amount of data, such as in VoIP applications such as Fring, web browsers and applications like Google Maps.

This problem affects the autonomy of all 3G handsets current crop. Regardless of manufacturer or model, virtually none can surpass the mark of two hours of continuous data transfer using the 3G network, including the iPhone 3G. This is not a design defect or lack of optimizations, but simply the fact that on a 3G network there is more work to do and more bits to transmit.

New control design, optimization software migration to new manufacturing techniques will reduce the amount incrementally over the next year, but the problem is not resolved from day to night. It may be that the battery in your smartphone bore 3 or 4 days in standby mode, but it will continue for only two or three hours in situations where the device need to work at full steam.