TM4C1294读不到有效地MAC地址是不是芯片根本没有预置MAC地址

        TM4C1294 MAC地址是不是每颗芯片都有内置的MAC地址，为什么我找了很多TM4C1294芯片的MAC地址都是0xFFFFFFFF，芯片都是新的，我使用的是官方例程的代码，一直读不到正确的MAC地址，是不是芯片根本没有预置MAC地址。

//
// Configure the hardware MAC address for Ethernet Controller filtering of
// incoming packets. The MAC address will be stored in the non-volatile
// USER0 and USER1 registers.
//
MAP_FlashUserGet(&ui32User0, &ui32User1);
//
// Convert the 24/24 split MAC address from NV ram into a 32/16 split MAC
// address needed to program the hardware registers, then program the MAC
// address into the Ethernet Controller registers.
//
pui8MACArray[0] = ((ui32User0 >> 0) & 0xff);
pui8MACArray[1] = ((ui32User0 >> 8) & 0xff);
pui8MACArray[2] = ((ui32User0 >> 16) & 0xff);
pui8MACArray[3] = ((ui32User1 >> 0) & 0xff);
pui8MACArray[4] = ((ui32User1 >> 8) & 0xff);
pui8MACArray[5] = ((ui32User1 >> 16) & 0xff);