I noticed that for serial port configuration for high baud rates is do incorrect. For baud rates above 760000 baud error increases significantly and for example for 921600 real baudrate is 490384 (error almost 50%)
I found that Freelink is based on DAPLink source code but it isn't public (freelink source).
In DAPLink serial port configuration https://github.com/ARMmbed/DAPLink/blob/1ae201863d2070d10c241ff16bd1f7d66d7accae/source/hic_hal/nxp/lpc4322/uart.c#L106 calculations is using with MulVal (varialble mv) value 15 but to FDR register is write value 1 so this is main problem but in fact configuration should be more complicated as described in user manual (UM10503) on page 1146
Should I report issue to DAPLink or NXP will fix this in own fork and release new Freelink firmware?