Subject: Re: UCC UART

From: Chuck Meade <[email-masked]>
Date: Tue, 22 Jun 2010 15:01:38 -0400

>> What BRGs did you choose for tx and rx?
> 
> BRG1 & BRG2

OK

>> Get a scope on the UCC3 tx pin and try to output some chars.  See if
>> there is
>> any digital activity on that pin at all.  If you are looking at a
>> terminal for
>> output, there are too many things that could be wrong between that tx
>> pin and
>> your display (e.g. level translation issue, null modem issue, baud
>> incompatibility,
>> terminal program set for XON/XOFF or HW flow control and UART not set
>> up compatibly).
>>
>> For now get the probe directly on the CPU's UCC3 Tx pin, output chars
>> and see
>> if there is any activity.
> 
> We've done all this - nothing on the pins directly at the CPU.
> 
> This is behaving very much like there is no clock to the device.
> Is there something special that needs to be done to get the BRGs
> to work?

If I was doing this, at this point I would do some strategic printk debugging
within ucc_uart.c.  You said that you are using 2.6.33.3, so you already have
all the fixes in ucc_slow.c that I had to backport to my older kernel.

If you question the setup of the BRGs, go to your function that sets them up.
I don't know about 2.6.33.3, but in the latest kernel it is qe_setbrg() in
qe.c.  At the very bottom there is an out_be32().
printk both the address, and the value that is being written to that address.
You may need to cast the values to unsigned longs to printk them.  I will look
at your numbers if you send them to me.  In my implemenation (which again was
a backport, so this may not apply to you) the BRG writes were off by 4 bytes.
But I think that this error was due to the backport -- a logic mismatch I
needed to resolve during the port.

Also in the current Linux kernel, there is a dependence on the correctness
of the "brg-frequency" property from the dts.  Look up above qe_setbrg() at
the qe_get_brg_clk() function.  Before the return (there are multiple return
points) printk the brg_clk being returned.  That must be correct for your
hardware -- must be the actual brg freq.  I assume that you are booting from
U-Boot.  I believe in modern implementations that U-Boot fills in the
brg-frequency in the device tree at boot time.

Let me know how it goes,
Chuck Meade
[email-masked]