Timing-Jitter on gpio output when LCD is active.

To clarify this: The realtime interrupt sets portpin to 1 uses tim13 to do a while loop doing a blocking wait.

Then sets the portpin to 0.

So there is no exit of the interrupt routine (timer interrupt not used).

Although the timing varies about 6us when lcd is active.

In the rt-interrupt routine we use __disable_irq to be sure nothing interrupts the realtime process.

What is the frequency of the TIM?

You are saying the pulse width varies by 6us?

Is the Frame buffer in internal SRAM or external SDRAM? Or on the display?

The jitter is in timing of successive rising edges, or in timing inside the pulse?

The application has allocated its data on this memory [external SDRAM shared with LCD framebuffer] too.

Bad idea.

In the 32-bitters, realtime stuff should be handled purely by hardware as much as possible. A simple stream of pulses can be generated by timers, more complex pulses pattern by a combination of timers and DMA.

Generally, the more the application goes towards 'general-purpose computing' and 'high computing power', the poorer the realtime performance; for multiple reasons.

JW

The jitter is in timing of successive rising edges, or in timing inside the pulse?

The rising and falling edge varies in time. As if the timer would not give accurate results. 

The application has allocated its data on this memory [external SDRAM shared with LCD framebuffer] too.

Bad idea.

Why is that? Does the communication between Displaycontroller and sdram affect the communication in the application code accessing the sdram? I store some data for the state machine in the sdram. Could it work better if i store the data in the internal SRAM?