It's of course synthesizable. If you don't specify OUT to be initialized to 0 (e.g. by initial block or general synthesis constraints), the statement might be synthesized as constant 1.
It's of course synthesizable. If you don't specify OUT to be initialized to 0 (e.g. by initial block or general synthesis constraints), the statement might be synthesized as constant 1.
This is definitely not synthesisable. Your code describes logic that is trying to detect a clock edge that is exactly CO incident with another clock edge, which is impossible.
This requirement is actually similar to the Type II phase comparator in the old CD4046B PLL except it goes high when one leads the other and low when it lags then becomes tri-state floating when in sync.
The output pulse width is thus a current pulse that can be integrated with a cap load to measure the phase error and for this mixer the PLL is in sync with coherent rising edges and the Vout integrates to what is required to keep the VCO at the same frequency and phase lock.
Thus this Type II mixer is called a Phase/Frequency detector.
The timing diagram of logic states appears below.
To realize this in code the CPU cycle counts must be tiny compared to the input clocks being compared to avoid the dead-time ambiguity.
Similarly in hardware , the dead-time is limited by the signal propagation latency.