Jens-Michael:
My recent experiments have shown that I receive the first byte of data from the slave (MSP430) to the master (CC25300) but none thereafter. I also get the first interrupt in the handler on the MSP430 slave and after processing it ( very tightly) I do not complete that in time to look or another USIIFG flag setting for the second byte. The interrupt handler simply hangs looking for USIIFG to be set.
So my conclusion is the baud rate even at 2440 is too fast. Per your reply I looked at the CPU clock I am using as that was set in the code long ago. To my surprise and lack of memory in order to avoid external components and ($) on my PCB and to have low power I am using the internal VLOCLK at 12khz. Yes khz! So no way I can be fast enough. Fortunately SPI operating fast is not a requirement. I will now continue to lower the baud rate on the CC2530 master and see if I can find a setting that works.
I guess potential fall back plans I have not studied would be to implement the SPI interface in code or maybe use I2C??
More later and again many thanks for the help.
Al McBride
SMART Light Systems