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by ramchip 5468 days ago
The radio CPU can be optimized for its job, so it may have extra instructions for error detection, decryption, etc. It may also be on a separate bus with the antenna peripherals, freeing up a lot of bandwidth for the main CPU.

It should be possible to do all this on a single CPU (real-time is no problem - just use an RTOS), but it would be expensive and eat a lot of power.
2 comments
bdonlan 5468 days ago
The other reason they split up the baseband and the main CPU is for regulatory reasons - the baseband is the only part talking to the radio, so it's the only part which needs to be thoroughly tested for regulatory compliance. This then lets them upgrade other parts more frequently without having to go through as much testing and obtaining approvals.
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samstokes 5468 days ago
real-time is no problem - just use an RTOS

In theory, yes, but the main smartphone OSes aren't RTOSes, and making them such requires nontrivial reengineering.

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