Hi, on Chrome OS devices, the architecture for sensors (such as accelerometer and gyroscope) involves the sensors being connected to an embedded controller, which receives interrupts from the IMU, collects samples, and then sends an interrupt to the main CPU running Linux. On the CPU, there currently is an IIO device called sensor_ring, which handles the interrupt by collecting the samples from the EC, and pushes them to an IIO buffer. As part of the EC --> AP communication mechanism, we collect: - the time (in EC clock) when the sensor notified the EC; - the time (in EC clock) when the embedded controller sent the interrupt; - the time (in Linux clock) when the CPU received the interrupt. We use these values (which we call respectively "a" "b" and "c"), as input to a median filter in order to both convert EC clock to Linux clock, and to smooth out jitter. We have since come to realize that a median is not the best filter for this task, and - as part of a larger redesign - would like to move this filtering in userspace and use a different filter (most likely either a least squares or a Kalman filter). However, doing the filtering in userland requires us to be able to send the a, b and c points from the IIO device on the kernel to userspace. My initial investigation led me to using indexing as the most viable option to have multiple IIO_TIMESTAMP channels defined for the same device. However, I spot a few places in the IIO framework where channels of kind TIMESTAMP seem to have special meaning. Is defining multiple timestamp channels via indexing a supported operation? If not, is there any way to define such channels? Or a better way to support our use case of providing 3 "timestamp" values to userspace. Any input is appreciated.
