Re: [RFC PATCH] docs/devel: add some notes on tcg-icount for developers

[Paolo Bonzini]

On 19/06/20 16:54, Peter Maydell wrote:
>> +
>> +MMIO isn't the only type of operation for which we might need a
>> +correct and accurate clock. IO port instructions and accesses to
>> +system registers are the common examples here. For the clock to be
>> +accurate you end a translation block on these instructions.
>> +
>> +.. warning:: (CONJECTURE) instructions that won't get trapped in the
>> +             io_read/writex shouldn't need gen_io_start/end blocks
>> +             around them.
> I think this is backwards -- instructions where icount is handled
> by io_readx/io_writex are the ones that don't need to be marked
> with gen_io_start. It's the i/o instructions that don't go through
> io_readx/io_writex that need gen_io_start.

Yes, and likewise instructions where icount is handled by
io_readx/io_writex need not terminate the TB.

Paolo