Gidday there,
We have a custom made board containing not much more than a Virtex-II Pro (v2p4) and 16 Megs of Mobile SDRAM. We are trying to port Linux, and in preparing we've successfully built kernels and code for a development board from Amirix.
But...
We have had a series of problems with getting u-boot to work. Firstly, this is a small Virtex-II, so we are unable to put everything into BRAM. So we've made a stripped down version of Amirix's ppcboot-lite, that is supposed to load u-boot, which then will load Linux.
Ppcboot-lite runs fine out of BRAM. However we've had several problems with executing from SDRAM. With various versions of the IPIF interface we have gone through the various Machine Check Exceptions problems with jumps to 0x700 and 0x200.
Now, it seems that we have found a working configuration (ipif v1.0.d) that lets us run code compiled by EDK (on WinXP under VMWare), but there is an odd problem with the same code compiled by our Linux cross-compiler.
We have some LEDs connected to memory mapped I/O, and our test code writes to it. The EDK compiled binary makes the following assembly for the output part.
stw r0,0(r9)
This works fine, and the LEDs blink all pretty and flashy like.
The Linux tools compile...
stw r9,0(r0)
However, the LEDs respond with blankity nothingness. Using XMD, we swap around these general purpose (according to how we read the docs) registers (r8,r10, r1 etc.) , and sometimes it works and sometimes it doesn't.
In the mailing-list archive, I've seen mention of a common SDRAM problem with u-boot, but it wasn't clear if this was just for Virtex-IIs or what.
Has anyone seen a problem like this? Is it our toolchain? Could it be signal integrity on our board? (we have slowed things on the bus down to 16MHz, just in case)
We are using crosstools-0.26, with gcc-3.3-20040112 and glibc-2.3.2.
Questions for clarification are welcome. Pointers, smack-up-side-the-heads, hints, cajoles, rants are also welcome.
Joshua Lamorie Department of Random Walks Xiphos Technologies Inc.