Re: [Cerowrt-devel] [Bloat] Comcast upped service levels -> WNDR3800 can't cope...

[Jonathan Morton <chromatix99@gmail.com>]

On 30 Aug, 2014, at 8:19 pm, Aaron Wood wrote:

> Do you think this is a limitation of MIPS as a whole, or just the particular MIPS cores in use on these platforms?  

There were historically a great many MIPS designs.  Several of the high-end designs were 64-bit and used in famous workstations.  The one we see in CPE today, however, is the MIPS equivalent of the AMD Geode, based on an old version of the MIPS architecture, and further crippled by embedded-style hardware choices.  It would have been a good CPU in 1989, considering that it would have competed against the 486 in the PC space, but it wouldn't have been hobbled by a 16-bit memory bus back then.

I'm not sure how much effort is going into improving the embeddable versions of MIPS cores, but certainly ARM seems to be a more active participant in the embedded space.  Their current range of embeddable cores scales from the Cortex-M0 (whose chief selling point is that it takes only a fraction of a square millimetre of die space) to some quite decent 64-bit multicore CPUs (which AMD is developing a server platform for), with a number of intermediate points along that continuum catered for.

So if a particular core works but proves to have inadequate performance, a better one can be integrated into the next version of the hardware, without any risk of having to rewrite all the software.  That future-proofing is probably important to manufacturers, and isn't very obviously available with MIPS cores.

I wouldn't be surprised to see something like a Cortex-A5, or possibly even a multicore Cortex-A7 in CPE.  These are capable of running conventional multitasking OSes like Linux (and hence OpenWRT), and have a lot of fully-mature toolchain support.  But perhaps they would leave out the FPU, or configure only the most basic type of FPU (VFPv3-D16), to save money compared to the NEON unit you'd normally find in a smartphone.

 - Jonathan Morton