Method and apparatus for generation of a system master timebase of a computing device using indirect signalling of timing information
View Patent ↗In a communication system comprising one master device and one or more slave devices, the slave devices synchronize to a common timebase maintained at the master device, independently of a wireless module timebase, without requiring transmission of accurate and real time master timer information from the master device. In one approach, a slave device sends timing information to the master device, the timing information representing the slave device timebase, and the master device sends back correction information to the slave device, the correction information representing a difference between the slave device timebase and the master device timebase, the correction information being usable independent of the timing of sending back the correction information. The master timebase might be a system master timer of an accurate timer based on a timer interrupt and a high resolution timer having a resolution greater than a timer interrupt resolution.
1. A method of creation of a system master timer, wherein the system master timer is usable to provide a system time reference for a plurality of network devices, the method comprising:
creating the system master timer based on a timer interrupt and a high-resolution timer having a resolution greater than a timer interrupt resolution, resulting in the system master timer having a higher resolution than a timer interrupt resolution,
determining a first value of the high-resolution timer at the start of a synchronization event that is triggered by the timer interrupt;
determining a second value of the high-resolution timer, the second value being the receipt time when a master device receives a signal with timing information from a slave device;
determining an elapsed time for a number of periods of the timer interrupt; and
calculating an adjustment of the system master timer from the elapsed time and the difference between the first value and the second value,
wherein the system master timer is a persistent timer, wherein a persistent timer is a timer that persists over a plurality of synchronization events.
2. The method of claim 1 , wherein the timer interrupt and high-resolution timer are not synchronized.
3. The method of claim 1 , wherein the timer interrupt and high-resolution timer are synchronized.
4. The method of claim 1 , wherein determining an elapsed time for a number of periods of the timer interrupt comprises:
determining an elapsed number of periods of the timer interrupt between the start of the synchronization event and the receipt time; and
calculating the elapsed time by multiplying the elapsed number times an interrupt period length.
5. A method of synchronizing a slave device timebase to a master device timebase, comprising:
sending timing information from the slave device to the master device, the timing information representing the slave device timebase; and
sending back correction information from the master device to the slave device, the correction information representing a difference between the slave device timebase and the master device timebase,
wherein the master device timebase is external to a wireless module, and is based on a timer interrupt and a high-resolution timer, the master timebase having a higher resolution than the timer interrupt; and
wherein the correction information is usable independent of the timing of transmissions from the master device and wherein the correction information is sent in one or more packets from the master device to the slave device and wherein the master device is not configured to transmit packets that include real-time accurate timing information.
6. The method of claim 5 , further comprising:
synchronizing a device to a first wireless network using the master device timebase; and
reusing the wireless module to communicate with devices in a second wireless network, wherein the device is the master device of the second wireless network and synchronizes to a common timebase without requiring transmission of accurate and real-time master timer information to achieve synchronization in the second wireless network.
7. A master device in a wireless network having master devices and slave devices, the master device comprising:
a transmitter that transmits packets such that the master device cannot provide a time of transmission of a packet to a slave device; and
a system master timer generator, that generates a system master timer based on a timer interrupt and a high resolution timer having a resolution greater than a timer interrupt resolution, resulting in the system master timer having a higher resolution than a timer interrupt resolution, wherein the system master timer is usable to provide a system time reference for a plurality of network devices and wherein the system master timer is a persistent timer, wherein a persistent timer is a timer that persists over a plurality of synchronization events,
wherein, after receiving timing information from a slave device, the master device sends back correction information to the slave device, the correction information representing a difference between the slave device timebase and the master device timebase.