On Sat, 4 Feb 2012, NeilBrown wrote:

On Fri, 3 Feb 2012 12:42:22 -0700 (MST) Paul Walmsley [off-list ref] wrote:

quoted

Case 1 is expected and is almost certainly not a bug.  As Neil mentioned 
it should be bps-rate dependent.  It occurs when the first character 
transmitted to the OMAP wakes the chip up via I/O ring/chain wakeup.
I/O ring/chain wakeup is driven by a 32KiHz clock and is therefore 
relatively high-latency.  So this could easily cause the first character 
or first few characters to be lost or corrupted, depending on the exact 
sequence of events, the low power state that the chip was in, etc.

A 32KiHz cycles every 30mSec.
At 115200 bps, there is one bit every 8.7 microseconds.

When I type "return" - which looks like 0101100001111... on the wire,
I see '0xC3' which looks like 011000011111... on the wire.
So we lost exactly 2 bits, or a delay around 17 microseconds.

I find it hard to reconcile that delay with the cause being a 32KiHZ clock.

If you're not disabling the HF clock oscillator via the AUTOEXTCLKMODE 
bits, the wakeup logic may be getting clocked by the sys_clk, which is 
quite a bit faster.  That might explain the corruption patterns you're 
seeing.


- Paul