Real time event determination in a universal serial bus system

In a computer system having a processor, a memory, a video controller, and a USB (universal serial bus) controller coupled to a system bus for interfacing peripheral devices on a USB cable to the computer system, a system for implementing a real time capability in at least one of the peripheral devices, comprising:

• a USB controller having a first register for storing a controller frame number and a second register for storing a controller frame remaining;
• a peripheral device having a third register for storing a device frame number and a fourth register for storing a device frame remaining, said peripheral device coupled to said USB controller via said USB cable;
• and
• a screen reference register coupled to receive said controller frame number and said controller frame remaining, said screen reference register coupled to said video controller to receive a reference signal and to store said controller frame number and said controller frame remaining in response thereto, said peripheral device transmitting said device frame number and said device frame remaining to said computer system in response to the occurrence of an event, said controller frame remaining and said controller frame number compared with said device frame remaining and said device frame number to determine a computer system time of the occurrence of said event.

In a computer system having a processor, a memory, a video controller, and a USB (universal serial bus) controller coupled to a system bus, a method for implementing a real time capability in a USB peripheral device, the method comprising the steps of:

• a) storing a controller frame number in a USB controller;
• b) storing a controller frame remaining in said USB controller;
• c) detecting an event in a peripheral device;
• d) storing a device frame number in said peripheral device in response to said event;
• e) storing a device frame remaining in said peripheral device in response to said event;
• f) transmitting said device frame number and said device frame remaining to said USB controller;
• and,
• g) comparing said device frame number and said device frame remaining with said controller frame number and said controller frame remaining to determine a reference time for said event with respect to said computer system.