A computer system is provided. The computer system includes a bus, a first master device, a second master device and a processor. The bus has a data line and a clock line. The first master device is coupled to the bus, detects a start phase of a first transaction on the data line, issues an interrupt message upon the detection of the start phase, and triggers a second transaction in response to a transaction indication message. The processor is coupled to the first master device, receives the interrupt message, and transmits the transaction indication message after a predetermined time interval upon reception of the interrupt message. The second master device is coupled to the bus and triggers the first transaction. The first transaction is finished within the predetermined time interval.