[U-Boot-Users] PXA270 board startup: printf does not work

[JP <jp-linux@att.net>]

Jerry Van Baren wrote:
> 
> Your talk about having a corrupted local char buffer confused me.  If it 
> were not for that detail, I would have been positive that you have a 
> problem with handling your UART's Tx busy flag.
> 
> Your symptoms are typical of not waiting for the UART to complete 
> transmitting a character before stuffing the next one in once the UART 
> FIFO is full.  The result is that, if the string has fewer than /n/ 
> characters (/n/ being the depth of the UART's Tx FIFO, possibly a few 
> more), it works OK.  If the string is longer than /n/, it gets corrupted 
> by your s/w overwriting characters in the UART.  Depending on the UART 
> implementation, this could include the one currently being shifted out, 
> resulting in garbage characters.

A very long (already initialized) string prints correctly with puts, so 
I suspect the FIFO implementation is OK.   We're using the FFUART.
> 
> What in your processor is 32 bytes long?  UART FIFO?  Cache line? Hmmmm, 
> could you be having cache consistency problems?  Cache problems would be 
> consistent with garbage in memory.
> 
> BIG WARNING NOTE: Writing memory with a debugger is typically very 
> benign (s.l.o.w.) compared to writing with the processor.  Writing 
> single memory locations with the processor is typically benign compared 
> to a cache line burst read/write.  SDRAM (including DDR/DDR2) 
> initialization problems typically do *not* show up until cache is 
> enabled because it is the burst read/write that violates the "S" in 
> SDRAM (you end up out of sync "synchronous").
> FAQ: <http://www.denx.de/wiki/DULG/SDRAM>

Thanks for those ideas.  We haven't found many examples to compare our 
configuration to, but we did have trouble initially getting the SDRAM 
startup sequence working.  Your description and the wiki entry describe 
what could be happening.

JP