Dear Nordic Team,
I was trying to use the I2C peripheral on the nRF5340 with clock speed of 1MHz, but I kept getting the error "unsupported speed". I was using the function call below for this:
i2c_configure(i2c_dev, I2C_SPEED_SET(I2C_SPEED_FAST_PLUS) | I2C_MODE_MASTER);
I noticed that the Nordic low level driver in NCS 1.8.0 seems to support this from the code below found in nrf_twim.h in the NRFX HAL
But the Zephyr driver for for Nordic does not (code snippet below taken from i2c_nrfx_twim.c)