I'm doing board bring up on a design using an MPC8308 and I'm seeing odd behavior when I try to read certain internal registers on the processor. In particular when I try to read the reserved registers in the DMA engine (for example offset 0xyyy2c008, right after the DMAES register) causes a machine check exception if I use u-boot and a "# SAP : read access failed" when using the BDI. Yes I know that it's a reserved register and all bets are off when it comes to those, so I'm not looking to find something "broken". What I'm curious about is why I've never seen this in the other processors I've used from Freescale (even other 83xx processors), and two why other "reserved" registers don't behave the same way. I can read all the way from 0xyyyy0d00 to 0xyyyy2000 just fine. So what's different about the DMA engine?
Don't think it's a BAT or a memory window issue since I can read on both sides of the register. Very curious.
Thanks for any insight.
Bruce