A payment reader includes a contactless interface for communicating with a contactless device. The payment reader has a processor that executes instructions stored in memory, and the instructions include instructions for a plurality of firmware modules including a message dispatcher module and a plurality of functional modules. The functional modules generate messages and the message dispatcher module stores the messages in a queued data structure such as a stack or a queue. The messages are provided to the functional modules from the queued data structure. Some of the messages are timed messages that are returned to the queued data structure.