We are running a survey to help us improve the experience for all of our members. If you see the survey appear, please take the time to tell us about your experience if you can.
Hi, i have just got a cortex-m0(LPC1114) based dev board. I'm reading about the architecture and instructions. My understanding is that it supports most thumb 16-bit instructions and a handful thumb-2 32-bit instructions. If the processor has a 32-bit bus which instructions are fetched(im assuming this, also i have limited knowledge of a CPU's inner workings), why don't it support more thumb-2 instructions? It seems like a waste, or maybe it fetches two 16-bit instructions?
My other issue is related to to my first question. I'm trying to set the core registers with immediate values using MOV. I read that you can use MOV for the for the 16 lower bits, and MOVT for the 16 higher bit(this is only for cores which supports ARM32 i suppose). However first it seems MOVT is not supported by cortex-m0, in arm-none-eabi-as: "Error: selected processor does not support Thumb mode `movt r0 , r1'. Also when i read the ARMv6-M reference manual, i read that MOV can only set a immediate value up to 8-bits long. This all seems very strange to me. I got a hint on a IRC that your really supposed to use PC relative addressing to set registers "directly", which i haven't read much into. Are there no efficient way to set immediate 32-bit values for registers, using MOV or other data instructions?
Thanks for responses!
Thanks for the great answer, that explains it! I'll just learn to use pc relative load instead.
Best Regards!