Debugging (step in, step over...) a target application is working until the StartOS function is called. This function initializes the System timer (STM). On TC3xx devices, usually that is the STM0 timer.
The timer is used by the scheduler to switch between the tasks. If you want to debug such code, timer(s) must be suspended, and hence the default initialization file must be used.
1. Use winIDEA Examples Workspaces in File | Select Workspace | Start with Example Workspaces.
2. Load a suitable initialization file. More information here.
Part of the initialization file that suspends STMs:
A STM0_OCS L 0x12000000
A STM1_OCS L 0x12000000
A STM2_OCS L 0x12000000
A STM3_OCS L 0x12000000
A STM4_OCS L 0x12000000
A STM5_OCS L 0x12000000