STM32F4 nanosecs delay

Question

I've been playing with SysTick for a couple of days and i cannot reach nanoseconds delay. Is it possible with Systick to reach such small values or i have to use timers and interrupts? The LEDs though won't work lower than 350ns delay. Here is an image from my usb oscilloscope:

In general I want to make a project (i am just experimenting with LEDs and SysTick above) which will be like this:

where Δt = 250ns (the other parameters will be determined somehow). The question is, can I make these pulses by using SysTick?

Answer 1

STM32F407VG have 24-bit SysTick timer and its maximum clock speed is 168MHz (Core Clock speed). That means, even if you set your SysTick reload register to:

0x000001 (1 cycle)

You can only have 5.95ns period.

Answer 2

I found this in section 6.2 Clocks of the RM0368 reference manual:

The RCC feeds the external clock of the Cortex System Timer (SysTick) with the AHB clock (HCLK) divided by 8. The SysTick can work either with this clock or with the Cortex clock (HCLK), configurable in the SysTick control and status register.

So maybe the maximum tick rate is limited by the clock divisions. Check Figure 12. Clock tree to see which clock config you should use to get maximum speed.