Reduction of IMU/AP link requirements for SDI
A method, controller and system in accordance with various aspects of the present disclosure facilitate reduced energy consumption in a motion sensing device having an inertial measurement unit (IMU), with a strap down integration unit, and an application processing unit (AP). The system and method include sensing acceleration values and rotational values at the IMU and converting the sensed acceleration and rotational values into velocity and orientation increments by strap down integration. The velocity and orientation increments are stored in a first buffer at the IMU between updates to the AP. When an update request is received at the IMU from the AP over an interrupt link, the buffer contents are transmitted over a serial link from the IMU to the AP.
1. A method for use in a motion sensing device having an inertial measurement unit with a strap down integration unit, and an application processing unit, the method comprising:
sensing at least one acceleration value and at least one rotational value at the inertial measurement unit; converting the sensed acceleration value and rotational value into velocity and orientation increments by strap down integration; storing the velocity and orientation increments in a first buffer at the inertial measurement unit; and receiving an update request at the inertial measurement unit from the application processing unit over a first link and in response transmitting the contents of the first buffer from the inertial measurement unit to the application processing unit over a second link.
2. The method for use in a motion sensing device in accordance with claim 1 , wherein the first buffer is a first in first out buffer.
3. The method for use in a motion sensing device in accordance with claim 1 , wherein the update request from the application processing unit is an interrupt signal.
4. The method for use in a motion sensing device in accordance with claim 1 , wherein the update request from the application processing unit is line clear signal.
5. The method for use in a motion sensing device in accordance with claim 1 , further comprising: detecting a high-frequency event at the inertial measurement unit; and in response to detecting a high-frequency event, and prior to receipt of the update request at the inertial measurement unit from the application processing unit over the first link, transmitting an event notification from the inertial measurement unit to the application processing unit over a third link between the inertial measurement unit and the application processing unit.
6. The method for use in a motion sensing device in accordance with claim 5 , wherein the inertial measurement unit further includes a second buffer, the method further comprising:
storing event data in the second buffer; and sending the stored event data in the second buffer to the application processing unit after an event is detected.
7. The method for use in a motion sensing device in accordance with claim 1 , wherein storing the velocity and orientation increments in a first buffer at the inertial measurement unit comprises combining the two oldest values in the first buffer so as to maintain the overall motion represented by the combined data to avoid buffer overflow.
8. A motion sensing system comprising: an inertial measurement unit having a strap down integration unit, the inertial measurement unit being configured to sense at least one acceleration value and at least one rotational value, convert the sensed acceleration value and rotational value into velocity and orientation increments by strap down integration and store the velocity and orientation increments in a first buffer at the inertial measurement unit to await an update request; an application processing unit linked to the inertial measurement unit via a serial data link and an update link, the application processing unit being configured to send an update request to the inertial measurement unit via the update link and in response to receive the contents of the first buffer from the inertial measurement unit via the serial data link.
9. The motion sensing system according to claim 8 , wherein the first buffer is a first in first out buffer.
10. The motion sensing system according to claim 8 , wherein the update request from the application processing unit is an interrupt signal.
11. The motion sensing system according to claim 8 , wherein the update request from the application processing unit is line clear signal.
12. The motion sensing system according to claim 8 , further comprising an event notification link between the inertial measurement unit and the application processor, and wherein the inertial measurement unit is further configured to detect a high-frequency event prior to receipt of the update request and, in response, to transmit an event notification from the inertial measurement unit to the application processing unit over the event notification link.
13. The motion sensing system according to claim 12 , wherein the inertial measurement unit further includes a second buffer and is configured to store event data in the second buffer and send the stored event data in the second buffer to the application processing unit after an event is detected.
14. The motion sensing system according to claim 8 , wherein the inertial measurement unit is further configured to combine the two oldest values in the first buffer so as to maintain the overall motion represented by the combined data to avoid buffer overflow while storing the velocity and orientation increments in the first buffer.