SAM3SD confusing flash size in CHIPID register

[mach]

Hello,

I'm using an SAM3SD (dual bank flash) MCU. When I read the CHIPID, I would expect NVPSIZ and NVPSIZ2 to be 256 K each. However, what I see is NVPSIZ = 512 K and NVPSIZ2 = 0.

Is this correct? Am I really working with an dual bank MCU? ARCH says I do?!