How can I generate a roughly 3 ms pulse on PG14 (=non-timer pin) when SystemCoreClock is 216 MHz?

[arnold_w]

I am working with the STM32F769 microcontroller (SystemCoreClock: 216 MHz) and I need to generate a roughly 3 ms pulse (negative pulse is also ok), that is always exactly the same, on pin PG14 for calibration purposes. According to STM32CubeMX, the pin can be configured as the following:

ETH_TXD1

FMC_A25

LPTIM1_ETR

LTDC_B0

QUADSPI_BK2_IO3

SPI6_MOSI

SYS_TRACED1

USART6_TX

GPIO_Input

GPIO_Output

GPIO_Analog

EVENTOUT

GPIO_EXTI14 

The only thing I can think of is to use the USART6_TX, but to make it run so slow I'd have to temporarily slow down the APB2 Prescalar. The microcontroller is running FreeRTOS with TIM6 as the TICK-clock and TIM6 is located on APB1 so I guess this solution is acceptable, but I would really prefer something where I don't have to fiddle with the clock settings. Can anybody please recommend something better?

[arnold_w]

Never mind, I realize I made a mistake, it works fine to clock the USART at 3333 Baud and with a word length of 9 bits I end up with a 3 ms negative pulse if I transmit 0b000000000. If an administrator sees this, please feel free to delete this thread.