[LinuxBIOS] SPD as debug channel

ron minnich rminnich at gmail.com
Sat Dec 2 00:40:43 CET 2006

It seems to me the order of choices is something like this:

1. USB debug port. This is going to work well in the x86 world, as
even the embeddec boards tend to have USB. USB is replacing rs232 in
those worlds. Based on the boards we have used in last 7 years, on
x86, setting up the PCI infrastructure at very early boot to use this
should not be hard. USB is almost always on bus 0. PowerPC sounds a
bit harder.
2. JTAG. This is very common on the PPC boards we have used. It is by
far the best option, since reflash after a disaster is possible,
debugging is easy, and so on. Rare on x86, common on PowerPC and ARM.

The next in line are:
3. SPD. Just as hard to get working as USB debug port on x86, since
SPD is on the south. Not useful on most x86 and PowerPC embedded
boards I have used, as they have no DRAM sockets of any kind -- and,
if you only have one, the usefulness is quite limited, since you have
to take the DRAM out to put the debugging in. But, most of the time,
you're debugging DRAM ...Requires that we design and build a card. I
don't think this approach is that practical.
4. LPC debugger. This one is kind of interesting, requires that we
build a card, but could have good use -- as long as LPC doesn't go
5. I2C snooper. Just solder onto I2C and use a card you build?

I still see (1) and (2) as the most practical.


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