I am still wrapping my head around ARM's licensing parctices.
I believe they sell general licneses to use their cores, then charge royalties per core shipped. They also sell licenses to physical IP that helps implement the cores in a given node and architecturall icneses if you want to customize a core design.
I suspect there may be a few other wrinkles in the ARM busienss model I am still coming up to speed on.
I would bet that there are a variety of terms for ARM cores out there, given the time period over which ARM has been operating and their relative negotiating strength. It might even be possible that Intel still has some of the agreement in place from DEC's license to produce the StrongARM architecture. It makes you wonder how things might have been different if Intel had not snubbed that path.
So I think XMOS might have purchased Architectural license. And then after modifying the design, making it capable of multicore and with other interfaces, if they sale the modified design to product manufacturers, what will be the charging pattern between XMOS, ARM and Product Manufacture? Does ARM licensing model allowing selling of the core? Will Product Manufactures have to pay to both ARM and XMOS? I hope there will be one more licensing model supporting this kind of modifications. I am sorry if I have kept too many questions here, but they are from a technical mind with less number of legal thoughts.
Whatever they are doing, they can't possibly be as confusing as the microsoft licensing program. When it comes to software licenses, microsoft has so many variations you need a sherpa to guide you through it.