42.7.5.4.4 Clock Stretching
In both Read and Write modes, it may occur that TWIHS_THR/TWIHS_RHR buffer is not filled/emptied before the transmission/reception of a new character. In this case, to avoid sending/receiving undesired data, a clock stretching mechanism is implemented.
Note: Clock stretching can be disabled by setting TWIHS_SMR.SCLWSDIS. In that case the UNRE
and OVRE flags indicate an underrun (when TWIHS_THR is not filled on time) or an overrun
(when TWIHS_RHR is not read on time).