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by david-given
3693 days ago
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The VC4's actually quite a nice processor; it's fun to write code for. 32 registers, massive DSP unit which I haven't looked into, instructions can be 16, 32 or 48 bits long (inline 32-bit constants!), FPU which shares registers with the integer unit, and some really interesting instructions for fast loops... (My favourite is addcmpb, which will increment a register by a constant or register, compare the result to a constant or register, and do a branch based on the result... all in a single 32-bit instruction. It's a for-next loop in a box.) ...but the downsides are that the FPU is single-precision only, doing 64 bit arithmetic is really hard, and the processor seems not to have any kind of MMU, which means that running real operating systems on it is likely to be very hard. |
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