Eliminating power drain

Working with their colleagues at Intel, engineers at Cambridge-based CSR have implemented a power-saving technique into their Bluetooth chips that will provide Intel-based laptops with up to an extra 30 minutes of battery life.

As part of the collaboration, the CSR engineers developed Bluetooth firmware and complementary Windows software which implements an Intel-developed power-saving technique called USB Sideband Deferring.

Their objective was to eliminate the power drain caused by frequent polling of the Bluetooth chip by the USB subsystem.

Intel mobile processors implement many techniques to save power. One of the most important is switching to low-power sleep states when idle. An important sleep state is called C3. An integrated USB Bluetooth device can prevent the processor from entering the C3 state because it needs to be constantly polled to check whether it has any data to send to the system. However, this constant polling prevents entry into the C3 state.

The technique developed by the two firms lowers power consumption by ensuring that the Bluetooth device is only polled when it has data to pass to the system. The rest of the time the processor can enter the C3 state.

Bill Nayavich, PC market manager at CSR, said: 'By working closely together, CSR and Intel have readdressed the way that Bluetooth interacts with the main system and therefore how much power is consumed within the notebook PC.'

The so-called Bluetooth Advanced Power Management is available now using firmware for CSR's Flash memory-based BlueCore4-External Bluetooth device. Equivalent ROM-based silicon will be sampling to customers in September 2008.