the problem was, that I had to wait for the CC1200 MISO pin to go low, after a reset strobe, before setting the chip select pin high again. I was kind of copying the approach from the CC110X driver implementation, where it configures the MISO pin as GPIO, waiting it to go low and then configuring the SPI pins again. Now the problem was, that I could not set and clear the chip select as I wanted, due to the problem, that the CC110X driver was doing the chip select in software, while configuring the SPI pins would force the CC2538 to do the chip select, as you suggested, in hardware. I now commented out the reconfiguration of the chip select as hardware, but will have to adjust it when the PR is merged. Thanks for the heads-up.