Re: [lwip-users] Low Iperf performance of lwip 1.4.1 on STM32 and FreeRTOS

[Jeff Barlow]

On 7/2/2013 4:50 AM, Claudius Zingerli wrote:
> In the final design, we plan use a 3-port switch from Micrel. It can be
> clocked from 25MHz or 50MHz, but the board I'm using to develop the
> software has a DP83848 that does need a 50MHz clock source for RMII.
> STM32F4 /might/ be able to handle 50MHz as a main clock source.

I see. For a one-off dev board I think it's always less frustrating to 
just use a separate 50MHz oscillator. The older PHY chips can be really 
fussy about clock jitter. I think once you get away from that DP83848 
you'll find things less painful.

I was just suggesting using the Micrel RMII clock output to feed the 
RMII clock input on the MCU. I've never tried feeding a 50MHz clock into 
the HSE on a STM32F407 but it strikes me as risky. I do seem to recall 
that some of the PHYs also have a direct 25MHz output that would work 
for that. Don't know if that includes your switch chip, however.
--
Later,
Jeff