Question: When changing the software-programmable PLL on the TMS320LC548, following the steps in the C54x CPU and Peripherals User's Guide (1996 SPRU131C) on page 8-20, can I be executing code during step 3 while I am waiting for the PLL to lock?

Answer: You shouldn't try to execute any time-critical code until the PLL is locked. What you can do during that time is to continually poll the Clock Mode Register PLLSTATUS bit (bit 0) to determine when the PLL is locked. If you initially came out of reset in DIV mode, the PLLSTATUS bit will change from 0 to 1 when the PLL is locked.