[U-Boot-Users] BITBANGMII implementation for MPC8548 eTSEC && 88E1111

Sam Song samsongshu at yahoo.com.cn
Wed Mar 7 10:56:44 CET 2007

Hi Ben,

Ben Warren <bwarren at qstreams.com> wrote:
> Time to reach into your engineering tool bag.


> controllers, coupling is loose.  You should be able to bitbang this
> provided the physical wires exist between the CPLD and the PHY.  I
> guess white-wiring the TSEC's MDC line isn't an option?

I did wire two CPLD GPIOs to MDC/MDIO of PHY.

> Stylistically, this leaves a lot to be desired, but if register 83
> (better to use hex here) really maps to the MDC and MDIO pins, it
> should work. 

Good catch. I did mistake 0x83 for 83:-(

> > Am I on the right track?
> >
> Before messing with the TSEC driver, try talking with the PHY using
> the 'mii' U-boot commands.  Also, pull out your oscilloscope and 
> check that the lines are toggling as you want. Once you're confident
> Bitbanged-MII works, integrate it into TSEC.

This is really a nice debug method. With it, we found that PHY
MDIO output HIGH level was too low - less than 1.5V. So CPLD took
it as '0' always. We pulled up it to 3.3V via a resistor and 
changed CPLD internal bank power supply level as 2.5/1.8V but 
no luck. Now hardware colleagues help us to work out another 
way to solve it. 

As the HIGH-Performance processors comes out, there is an extra 
workload to debug those broken board besides normal development.
No easy to drop it as before. Luckily, u-boot's rich features 
and the poweful resources make it easier than it should be.

Thanks a lot,



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