I would like to know what's the use of the SPI dummy read in BMI160, and What is the minimum delay time needed after dummy SPI read for BMI160?
BMI160 supports both I2C and SPI interface but has no PS (protocol select) pin. It starts with the I2C interface enabled and if there is a raising edge on the CSB line, it will switch to the SPI protocol. The sensors needs at least a 140us delay after the first SPI dummy read operation to make sure the bus switch was successful.