This article will discuss the ARM Cortex A7 processor architecture. Semiconductor products based on it can be found in smartphones, routers, tablet PCs and other mobile devices, where it until recently held a leading position in this market segment. Now it is gradually being replaced by newer and fresher processor solutions.
Brief information about ARM
The history of ARM began in 1990 when it was founded by Robin Saxby. The basis for its creation was a new microprocessor architecture. If before that the dominant position in the CPU market was occupied by x86 or CISC, then after the formation of this company, a worthy alternative appeared in the form of RISC. In the first case, the execution of the program code was reduced to 4 stages:
- Get machine instructions.
- Performing microcode conversion.
- Getting microinstructions.
- Step-by-step execution of microinstructions.
The main idea of the RISС architecture was that the processing of program code can be reduced to 2 stages:
- Get RISC instructions.
- Processing RISC instructions.
Both in the first and in the second case there are both pluses and significant drawbacks. x86 successfully conquered the computer market, and RISC (including ARM Cortex A7, introduced in 2011) - the mobile device market.
The history of the appearance of the Cortex A7 architecture. Key Features
Cortex A8 served as the basis for the Cortex A7. The main idea of the developers in this case was to increase the performance and significantly improve the energy efficiency of the processor solution. This is what ultimately happened to the engineers at ARM. Another important feature in this case was that it became possible to create a CPU with big. LITTLE technology. That is, a semiconductor crystal could include 2 computing modules. One of them was aimed at solving the simplest tasks with minimal power consumption, and, as a rule, the Cortex A7 cores acted in this role. The second was designed to run the most complex software and was based on the Cortex A15 or Cortex A17 computing units. Officially, "Cortex A7" was presented, as noted earlier, in 2011. Well, the first ARM Cortex A7 processor was released a year later, that is, in 2012.
Production technology
Initiallysemiconductor products based on A7 were produced according to the technological standards of 65 nm. Now this technology is hopelessly outdated. Subsequently, two more generations of A7 processors were released according to tolerance standards of 40 nm and 32 nm. But now they have become irrelevant. The latest CPU models based on this architecture are already manufactured according to 28 nm standards, and it is they that can still be found on sale. A further transition to newer technological processes with new tolerance standards and outdated architecture is hardly to be expected. Chips based on A7 now occupy the most budgetary segment of the mobile device market and they are gradually being replaced by gadgets based on A53, which, with almost the same energy efficiency parameters, has a higher level of performance.
Architecture of the microprocessor core
1, 2, 4 or 8 cores can be part of an ARM Cortex A7 based CPU. The characteristics of the processors in the latter case indicate that the chip contains essentially 2 clusters of 4 cores. For 2-3 years, entry-level processor products were based on chips with 1 or 2 computing modules. The middle level was occupied by 4-core solutions. Well, the premium segment was behind 8-core chips. Each microprocessor core based on this architecture included the following modules:
- Floating Point Unit (FPU).
- Cash level 1.
- NEON block for CPU optimization.
- ARMv7 compute module.
There were also the following commoncomponents for all cores in the CPU:
- Cash L2.
- CoreSight core control unit.
- AMBA data bus controller with 128 bit capacity.
Possible frequencies
The maximum clock frequency for this microprocessor architecture can vary from 600 MHz to 3 GHz. It should also be noted that this parameter, which indicates the maximum impact on the performance of the computing system, varies. Moreover, the frequency is influenced by three factors at once:
- The level of complexity of the problem being solved.
- Degree of software optimization for multithreading.
- Current value of semiconductor crystal temperature.
As an example, consider the algorithm of the MT6582 chip, which is based on A7 and includes 4 computing units, the frequency of which varies from 600 MHz to 1.3 GHz. In idle mode, this processor device can have only one calculation unit, and it operates at the lowest possible frequency of 600 MHz. A similar situation will occur when a simple application is launched on a mobile gadget. But when a resource-intensive toy with optimization for multithreading appears in the task list, all 4 program code processing units at a frequency of 1.3 GHz will automatically start working. As the CPU heats up, the hottest cores will lower the frequency value or evenswitch off. On the one hand, this approach provides energy efficiency, and on the other hand, an acceptable level of chip performance.
Cache
Only 2 cache levels are provided in ARM Cortex A7. The characteristics of the semiconductor crystal, in turn, indicate that the first level is necessarily divided into 2 equal halves. One of them should store data, and the other - instructions. The total cache size at the 1st level according to the specifications can be equal to 64 KB. As a result, we get 32 KB for data and 32 KB for code. The 2nd level cache in this case will depend on the specific CPU model. Its smallest volume can be equal to 0 MB (that is, absent), and the largest - 4 MB.
RAM controller. Features
Built-in RAM controller comes with any ARM Cortex A7 processor. The characteristics of the technical plan indicate that it is focused on working in conjunction with LPDDR3 RAM. The recommended operating frequencies of the RAM in this case are 1066 MHz or 1333 MHz. The maximum RAM size that can be found in practice for this chip model is 2 GB.
Integrated Graphics
As expected, these microprocessor devices have an integrated graphics subsystem. ARM recommends the use of its own Mali-400MP2 graphics card with this CPU. But its performance is often not enough to unlock the potentialmicroprocessor device. Therefore, chip developers use more powerful adapters in combination with this chip, for example, Power VR6200.
Software Features
Three kinds of operating systems target ARM processors:
- Android from search giant Google.
- iOS by APPLE.
- Windows Mobile by Microsoft.
All other system software has not received much distribution yet. The largest market share of such software, as you might guess, is occupied by Android. This system has a simple and intuitive interface and entry-level devices based on it are very, very affordable. Up to version 4.4 inclusive, it was 32-bit, and since 5.0 it began to support 64-bit calculations. This OS successfully runs on any family of RISC CPUs, including ARM Cortex A7. The engineering menu is another important feature of this system software. With its help, you can significantly reconfigure the capabilities of the OS. Access to this menu can be obtained using a code that is individual for each CPU model.
Another important feature of this OS is the installation of all possible updates automatically. Therefore, even new features may appear on the chips of the ARM Cortex A7 family. Firmware can add them. The second system is aimed at APPLE mobile gadgets. Such devices mainly occupy the premium segment and have corresponding levels of performance and cost. The latest OS in the face of Windows Mobile has not yet receivedgreat distribution. There are devices based on it in any segment of mobile gadgets, but a small amount of application software in this case is a deterrent for its distribution.
Processor models
The most affordable and least productive in this case are 1-core chips. The most widespread among them was MT6571 from MediaTek. Up a notch are the ARM Cortex A7 Dual Core CPUs. An example is the MT6572 from the same manufacturer. An even greater level of performance was provided by Quad Core ARM Cortex A7. The most popular chip from this family is MT6582, which can now even be found in entry-level mobile gadgets. Well, the highest level of performance was provided by 8-core central processors, to which the MT6595 belonged.
Further development prospects
So far you can still find mobile devices on store shelves based on a semiconductor processor device based on 4X ARM Cortex A7. These are MT6580, MT6582 and Snapdragon 200. All these chips include 4 computing units and have an excellent level of energy efficiency. Also, the cost in this case is very, very modest. But still, the best times of this microprocessor architecture are behind us. The peak of sales of products based on it fell on 2013-2014, when it had practically no alternative on the mobile gadget market. Moreover, in this case we are talking about budget devices with 1 or 2computing modules, and with flagship gadgets with an 8-core CPU. At the moment, it is gradually being forced out of the market by Cortex A53, which is essentially a modified 64-bit version of A7. At the same time, she retained the main advantages of her predecessor completely and completely, and the future is definitely hers.
Opinion of experts and users. Real reviews about chips based on this architecture. Strengths and weaknesses
Certainly, the appearance of the ARM Cortex A7 architecture of microprocessor devices has become a significant event for the world of mobile devices. The best proof of this is that devices based on it have been successfully sold for more than 5 years. Of course, now the capabilities of the A7-based CPU are no longer enough even to solve mid-level tasks, but the simplest program code on such chips still functions successfully. The list of such software includes video playback, listening to audio recordings, reading books, surfing the web, and even the simplest toys in this case will start without any problems. This is what the leading thematic portals dedicated to mobile gadgets and devices focus on, both leading experts of this kind and ordinary users. The key disadvantage of A7 is the lack of support for 64-bit computing. Well, its main advantages include the perfect combination of energy efficiency and performance.
Results
Certainly, the ARM Cortex A7 architecture is a wholeera in the world of mobile devices. It was with its advent that mobile devices became affordable and quite productive. And the mere fact that it has been successfully sold for more than 5 years is another confirmation of this. But if at first gadgets based on it occupied the middle and premium segments of the market, now they are left with only the budget class. This architecture is outdated and is gradually becoming a thing of the past.
