The previous versions of the Raspberry Pi – the Models A, A+, B and B+ – all featured a Broadcom BCM2835 ‘System on a Chip’ with a 700MHz single-core ARM11 processor, whereas the version 2 Model B features a Broadcom BCM2836, in which the ARM11 part has been updated to a 900MHz quad-core ARM Cortex-A7.
The other significant change is that the new version sports 1GB RAM, twice as much RAM as the B+ and the second revision B, and four times as much as the A, A+ and original B. Everything else remains the same – including the price, which is typically quoted as US$35.
What does this mean for RISC OS?
Perhaps most important is the change of processor: The ARM11 part was an ARMv6 processor, which featured an ARMv5 compatibility mode. The Cortex-A7 found on the new PI, however, is an ARMv7 processor.
The XScale processor used in the IyonixPC was an ARMv5 part, so (excepting anything which may have directly addressed the computer’s hardware) third party software that was compatible with the Iyonix was already compatible with the Raspberry Pi when its CPU was running in ARMv5 compatibility mode.
Being an ARMv7 part, however, the processor on the new board is like the one found on the BeagleBoard and PandaBoard – so the same compatibility issues that affect RISC OS software on those platforms will also be applicable to the Raspberry Pi 2; most notably the issue of alignment exceptions.
For the operating system itself, RISC OS Open Ltd had already been developing a version of RISC OS behind closed doors while the Pi 2 was in development, although there was obviously an embargo in place which meant details of the new board couldn’t be released; updates to the published source tree that mentioned the Raspberry Pi 2 therefore didn’t start appearing until after the announcement, and beta versions of the ROM image are now becoming available (for which the latest firmware is needed, along with the line framebuffer_swap=0 in the config.txt file, to cope with the red and blue colour components being swapped). Being beta versions, these should be used with caution – but the bottom line is that we’re covered.
Another thing the new processor should bring is an increase in speed.
If you have been keeping up with the more general Raspberry Pi news, you might have read that the speed increase can be as much as six times – but that sort of increase isn’t going to be seen by RISC OS users; a major factor in that figure is the change from a single-core processor to a quad-core one, a feature that will massively benefit software that is able to take advantage of multiple processor cores. RISC OS, sadly, is unable to do that.
Instead, we can only benefit from the increase in clock speed from 700MHz to 900MHz, and perhaps other changes in the processor architecture. The increase in clock speed is just shy of 30% – so looking at things very simply, that suggests a 30% increase in speed as a result of that alone. However, whether that will actually be the case will depend on the software you are using, and what it’s doing – although in some cases a slower speed is being reported, but it’s still early days as yet.
If you want to see a Raspberry Pi 2 Model B in action, check out the RISC OS Open stand at the Southwest Show on Saturday, 21st February, 2015 – and if you pop along to the CJE Micro’s stand, you might even be able to buy one!