SPI frequency setting is not accurate in Portenta H7

[abyanu]

For example the following statement
SPI.beginTransaction (SPISettings (1000UL * 1000, MSBFIRST, SPI_MODE0)) ;
should set the SPI to 1MHz but the actual measured frequency is 631KHz

with the following settings
SPI.beginTransaction (SPISettings (4000UL * 1000, MSBFIRST, SPI_MODE0)) ;
SPI is set to 4MHz but the actual measured frequency is 2.4MHz