I'm attempting a custom PCB with a SAM3S on it. The datasheet makes the following comment about power-up considerations:
5.2.2 VDDIO Versus VDDIN At power-up, VDDIO needs to reach 0.6 V before VDDIN reaches 1.0 V.
How on earth do you make this happen without some non-trivial external control? Interestingly, all of the typical powering schematics on p21/22 of the datasheet show VDDIO and VDDIN connected together.
Edit: the SAM3S-EK2 schematic also shows them tied together but with a 10uF cap on VDDIN, maybe to suppress it while VDDIO is directly connected to the 3.3V bus?