I've been asked is there a way to know exactly when STP recalcs occur and im not sure there is. I know you have the "sh spanning-tree detail" command and that shows when the last TCN was received and from where but i dont think that necessarily mean it was a spanning-tree recalculation.
Also have been asked to setup SNMP to send email alerts whenever a STP recalc occurs. Never seen SNMP trap for that, so im pretty sure im being asked to do something that isn't possible.
If it matters we use Nexus 7ks for our core switching.