DW1000 TXSTRT Immediate Frame Transmission Delay


I am facing an issue regarding the immediate frame transmission capability of the DW1000.

I properly prepare a frame transmission with all necessary configurations.

However, after the immediate transmit start bit (TXSTRT) is set it takes 6 microseconds until the DW1000 issues the transmit frame begins interrupt (TXFRB), as shown on the picture below:

Of course, I made sure that the DW1000 is in IDLE state prior to starting the frame transmission and therefore it should not take that long until the frame transmission starts, as shown in the datasheet:

In addition, I also made sure that all previous interrupts and especially the TXFRS interrupt have been properly cleared, so I can also rule out the issue described in the application note APS022, as shown below:

All in all, my question is what can cause this 6 microseconds delay?

I expected that the transmit frame begins interrupt gets issued immediately after starting the frame transmission. However, this is obviously not the case.