Asynchronous reset and synchronizers

Thanks for your answers, Tricky!

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Just to add - remember that all of the registers in Altera fabric have asynchronous resets on the regsiters, which is why this is the recommended way to do a reset. Synchronous resets are only emulated, unlike xilinx where all resets are synchronous.

Another tip is to only reset those that need it rather than all of them, as this can help the fanout and reduce routing resources.

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Actually that depends on the device and is not always entirely clear in Altera's documentation.

For example, the Arria 10 is supposed to have both synchronous and asynchronous resets on its registers. The number of CC resources is much higher when using synchronous reset, but that's due to the local routing, apparently. So while the asynchronous reset will take one additional global routing (when the fanout justifies it), it relieves the non-global routing a lot, especially when resetting all registers.

Same for the older Stratix 5, although the documentation states "The ALM directly supports an asynchronous clear function" and a few lines below, also specifies that each register has synchronous/asynchronous clear signals.