We have a custom board with imx6ul processor and LPDDR2. We are using PN532 NFC on uart. We observed that at low cpu frequency (198000 KHz) there were many failure cases while reading NFC tag due baud rate mismatch and also our python application (to continuously read ADC data) execution becomes very slow. No problem was observed when we operated board at highest frequency (528000KHz). We tested same thing on imx6ul evk board at low frequency, but in this case every thing was working fine (NFC and python application). We didn't observe any failure case while reading NFC tag or our python application becoming slow.
Thus my question why their is so much difference in board performance at low cpu frequency? Is this due to LPDDR2? Both LPDDR2 and DDR3L are 400MHz.