We have an SBC board, in the style of the Leopardboard or Beagleboard, that is misbehaving. It's based on the Leopardboard design (TI-DM368 CPU, DDR2 RAM, NAND Flash).
Developing software on the leopard all works well. However, the 1st prototype board turned up and refused to boot. Investigation lead us to the point where slowing the clocks (ARM & DDR) down means the board will boot.
The hardware (either board layout, termination, DDR chip, whatever) is the #1 suspect, as we can run identical software on the Leopard and it works fine. Unfortunately, the nature of the fault means we can't boot into linux to run strenuous RAM tests that may provide better diagnostics.
From the hardware side, the DDR clock is one of 345MHz, 486MHz, 680MHz depending on the clocking settings - beyond the scope of any of our scopes or logic analysers.
So - it's sort of two questions in one really:
From the hardware point of view, other than "rent a faster scope", is there an approach to diagnosing this with what's to hand? We have 200MHz DSO's, <100MHz logic sniffer, and 1.5GHz spectrum analyser to play with.
From the software point of view (I know, wrong forum) if anyone has tips or code snippets on exercising DDR RAM, they'd be greatly appreciated.
Edited to add the answer:
Well we borrowed a Tektronix 7104 and it worked so well we didn't even have to touch the board with it ;)
The problem revealed itself to be a sagging 1v3 power supply line being strangled by 0402-size SMT ferrites.
The symptoms were that, near the marginal operating frequency, the board would boot but lock when a memory-hungry / high-bandwidth video streaming process tried to start. This, coupled with the fact that running slower made it work OK, led us to believe it was a frequency-related issue when in fact the lower clock frequency was also putting less load on the power supply components.
The 0402 ferrite beads used for filtering were going surprisingly high impedance as the current went up, dropping a critical supply line below the allowable operating point.
Unfortunately this means I can't give the "winning answer" to Dave Tweed, but it does mean our board now works. Even better, it's the boss's fault not mine!
Oh and Tek 7104's are freakin' awesome feats of electronic engineering. If you've never looked at how they work, it's pure analogue kung-fu.