[Elphel-support] IMU/GPS/PPS message latency

[Lee Lemay]

Dear Elphel folks,
 
I'm interested in decreasing the latency at which the IMU/GPS/1PPS data is made available by the FPGA to the CPU. I understand that the CPU cannot handle high frequency interrupts, so we will have to work around that.
 
I thought that there would be several possibilities to lowering the latency of the IMU/GPS/1PPS data.
1. Decreasing the size of the FPGA DMA buffer. This will lead to more frequent interrupts, as the buffer fills up more quickly.
2. Reducing the type of data logged. I am only interested in GPS/IMU/1PPS data. It seems that a log message is created for every photo that is taken - removing the "photo logs" will make transmitting/processing the logs more efficient.
3. Adopting a polling scheme, where the CPU does not respond to an interrupt when the DMA buffer is full, but rather polls the DMA buffer. This might require too much re-engineering to be feasible.
 
Please let me know if these ideas make sense, and where in the source code I should start looking to make these changes happen.
 
I appreciate your help!
Lee
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