25 May 2010
Seminar hears how Cortex-M range is helping software and hardware designers
For the longest time, ARM has been closely associated with the mobile phone market and more than 80% of all phones now feature an ARM processor. But over the last few years, the company has turned its attention to the general purpose, or industrial, marketplace.
In the main, this has been done under the Cortex banner. Three 'variants' have been announced – the A, M and R series. Of these, the M series has seen a lot of recent activity. And a seminar held last week by Hitex took a look at how demand for Cortex based microcontrollers has been developing.
Providing the keynote for the one day event was Brian Lawrence, solutions marketing manager for ARM. He noted the big push of the last few years had been the move from 8 and 16bit mcus to 32bit devices. "It's quite radical," he believed, "because, while most applications can be handled by 8 and 16bit devices, the move is being driven by the market. It's because of such factors as the level of connectivity demanded. Products aren't standalone black boxes any longer," he contended. "They have to tell someone that they're doing something interesting."
Lawrence sees a number of industry 'hot spots' to which he believes the Cortex range of microcontroller cores is well suited.
"Energy use, cost and safety are all issues today," he said, "and motor control is one of the biggest issues." In his opinion, if users can save 10% of the energy consumed by motors, it would make a big difference as motors currently represent 54% of all energy consumption.
More than 70million Cortex-M devices were shipped last year and the M range is now seeing more activity than the –A and –R variants. "Nowadays, everyone is driven by cost, regardless of design and complexity," Lawrence believed. "And there are now four companies selling Cortex-M based mcus for less than $1 in volume and this dispels the myth that ARM is a premium product."
Another burning issue is software complexity. "Development tool chains are becoming more important," he stated. "While hardware costs have decreased, the software development effort has gone up. Where it used to be 1:3 hardware to software, most high end projects are seeing a 1:10 ratio. That means we all have to think intelligently about how software is written.
"The reuse of code is becoming more and more important, something unheard of a few years ago. Today, software such as protocol stacks are being moved from project to project."
Picking up on the software themes in Lawrence's keynote, Hitex sales director Trevor Martin outlined the benefits of CMSIS, the Cortex Microcontroller Software Interface Standard.
"With more complex mcus appearing, designers are having to use third party software in order to get projects out of the door," he said.
"But in order to use third party software with confidence, there needs to be an interface standard. CMSIS acts as that standard for those writing code for Cortex-M mcus."
CMSIS has a core peripheral access layer, which defines naming and address conventions, and provides helper functions to access core registers and peripherals. There is also a middleware access layer that provides common ways to access peripherals.
"The good thing about CMSIS is that it isn't a large and complex affair; it requires only 1k of code and takes up just 4byte of memory."
Martin said CMSIS provides users with the benefit of a consistent framework within which to work. "The code conforms to MISRA C 2004," he noted, "it uses ANSI data types and has standard interrupt handling. From the programmer's point of view, CMSIS software is the same, it's just a matter of changing the engine."
Providing another software perspective was Richard Barry, head of innovation at Wittenstein High Integrity Systems. He addressed the issue of safety integrity, outlining the steps that developers need to address when developing software for such applications. He believes the Cortex-M architecture makes the software certification process onerous. "The good thing about this architecture is that time and interrupt control are part of the mcu core. Therefore, these items are identical across all M3 based microcontrollers."
While this may not seem an obvious benefit, Barry explained: "All documentation can remain the same, even though a different mcu has been used. Nearly all the code is identical, which makes things much easier."
And he believes the Cortex-M architecture brings simplicity to critical software development. "The PendSV file is the only place where context switching takes place. Because there is little or no variation between vendors at the core level, using the Cortex-M3 in safety critical applications means less source code is needed and the source code can be simpler."
Author
Graham Pitcher
Supporting Information
Websites
http://www.arm.com
Companies
ARM Ltd
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