Hi Bob:
I got a new issue is after I select the PIOSC as clock source and cut off main oscillator signal , it would keep waiting SYSCTL_PERIPH_EPHY0 ready (use the function SysCtlPeripheralReady)when MCU initial the Ethernet module.
I refer the data sheet of TM4C1294KCPDT, on page 1407,it describe that Ethernet Controller Module and Intergrated PHY recive two clock inputs. One is gated system clock and other is MOSC. As my personal opinion, does it means that Internal PHY must be drive by MOSC ? If so, this could explain why I cut off MOSC, it would keep waiting the registet state ready,once I recover the MOSC signal,it could get through the initialization which even use PIOS as clock source.