Remember that these days ARM designs processor 'cores' which are the inner fundamental components inside processor chips. Usually, third party companies and manufacturers then license the rights to take these core designs and put them in custom designed chips to form a full processor. This means a company could take an ARM9 core and package it up in a chip that features LCD and wireless support circuitry to make a processor designed ideally for small portable devices.So, it's therefore unusual to pick up a chip now with just an ARM processor core in it, like the processors in the ARM610, ARM710 and StrongARM daughter cards for RiscPCs. However, it does mean that ARM based processor chips contain built in useful functionality.
Processor cores suitable for RISC OS:
ARM 7 family [details]
We're all pretty much familiar with cores from this family, as seen in the ARM710 processor chip and the Cirrus PS7500FE. Cirrus offer other processors powered by the ARM 7 family including three chips aimed at portable products that use the ARM720T core. The ARM720T is a good modern core designed for embedded and low power products, like MP3 players and digital cameras. The core clock speed can run up to 100MHz.
ARM 9 family [details]
We're now entering the territory of intelligent consumer based eletronics where Symbian OS, Palm OS, Linux and Windows CE roam. The ARM920T core can be used in products such as next generation mobile phones, PDAs and set top boxes and ARM suggest clock frequencies of up to 200MHz. Earlier this week, Samsung boasted an ARM920T based processor, clocked at 533MHz. Their S3C2440 chip, which features the ARM 920T core, is touted as "the world's fastest mobile CPU" and includes built in support for LCD displays, interface for a touch screen and support for USB.ARM 10 family [details]
The ARM 10 family is aimed at digital consumer projects and also industrial control systems. While the ARM1020E core is a 32 bit processor with 16 bit Thumb support, a 64 bit internal bus and digital signal processing (DSP) extensions. It also has a clock frequency of 325MHz. We're not aware of any high profile use of this core although last year, Samsung spoke of using an ARM 10 core in a 400-600MHz processor for PDAs. Samsung also said last year they had an ARM core capable of running at 1.2GHz. The 1GHz barrier breaking ARM1020E compatible core, nicknamed Halla, was said to be ready for sampling by Q3 of 2003.
ARM 11 family [details]
The ARM 11 family is really pushing into specialised areas. This family of cores focuses on applications where memory is a premium and there is a need for high performance, real time processing with low power consumption. This means wireless, sub-notebook computers and networking devices. ARM offer clock frequencies up to 400MHz for this family. We're not aware of any ARM 11 cores being widely available, however around this time last year, the EE Times reported that ARM wanted to control the release of their ARM11 based cores.
Intel XScale [details]
The XScale core is currently overseen and packaged into integrated chips by Intel as a result of Intel buying DEC and thus the StrongARM design that ARM and DEC created. The XScale was once upon a time dubbed the 'StrongARM 2' and current cores are ARM architecture and code compliant. The XScale core can be found in numerous flavours of processor chips that are highly integrated with additional features to suit the markets Intel are aiming at. Firstly, there's the PXA26x family of chips designed for wireless products and mobile phones - by now you've probably started seeing a trend in the suggested applications of these ARM based chips. The PXA26x family offers clock frequencies of 200-400MHz and supports storage cards (such as CompactFlash), USB and the Bluetooth wireless standard. The PXA255 processor also runs between 200 and 400Mhz and also supports PCMCIA, other storage card media, USB and Bluetooth wireless.Next, we move onto the familiar XScale I/O processor family. The IOP321, as used in the Castle Iyonix, runs at 600MHz and provides PCI interface and DDR SDRAM support. The 733Mhz IOP310 is a two chip chipset but is slower than the IOP321 in terms of PCI bus speed and DDR SDRAM access speed. The IOP200 is unlike the other ARM based processors we've seen here as it's a straight ARM compatible processor with no special integrated abilities. It can have a clock frequency as high as 733MHz. You can read a run down of what the XScale IOP321 brings to RISC OS here.
Will we see ARM processors breaking the golden 1GHz barrier? We have to consider that ARM processors are going into mobile gadgets where power usage is critical or into devices that don't need to go beyond 1GHz. However, this may one day all change.
"Desktops today are (consuming power of) 75 to 100 watts and when you go to handheld devices you are typically operating at less than 1 watt," said Pat Gelsinger, Intel's chief technology officer speaking at the Intel Developer Forum in Japan last October. "Obviously, you are optimizing the design for different criteria. So today, if I was going to look at a StrongArm core or XScale core, could I create a 2GHz or 3GHz XScale today? Absolutely. Could I do so and deliver the best trade-off of power and performance inside a 1-watt envelope? No. You tend to design the chips differently to live inside different devices."
Summary
The bottom line is RISC OS can be employed on any available processor that features an ARM7 to ARM11 or XScale core and a suitable memory management unit (MMU). A processor's MMU provides flexible manipulation and control over the memory and memory mapped hardware in a device.
With these new processor cores unlocked, the leaping of RISC OS from the Iyonix to existing ARM based PDAs and similiar gadgets will rely on the availability of drivers for the proprietry PDA hardware. The HAL in RISC OS 5 enables the OS developers to adapt RISC OS to vital systems like hardware timers, clocks, interrupts and interfaces provided by new chipsets. With this and 32 bit compatibility out of the way, it's now largely down to the substantial work required to produce the necessary device drivers for newer hardware.
Links
RISC OS 5
ARM
ARM processor cores
Intel
Intel XScale processors
With thanks to David Ruck, Martin Wuerthner, Steffen Huber and Ian Jeffray for their individual assistance.