topic Re: MDC frequency generation issues in i.MX RT Crossover MCUs

MDC frequency generation issues

jautry — Sat, 08 Oct 2022 01:07:36 GMT

In the iMXRT spec, it states that if 50Mhz is used for the reference clock then placing a value of x9 in the MSCR register should provide the 2.5mhz MDC clock to the ethernet phy. Unfortunately, when I do that, I get a higher frequency around 7mhz. I measured the ref_clock and it was at 50mhz. Are there other dividers somewhere which affect this, or do I have some clocking mis-selected. I have to place a value of around 0x40 in the MSCR register to get the proper frequency.

Re: MDC frequency generation issues

xiangjun_rong — Sun, 09 Oct 2022 09:37:03 GMT

Hi,

As the following pic, you can write the

ENET->MSCR&=~(0x3F<<1);

ENET->MSCR|=0x09<<1;

BTW, for your code, in the debugger, pls check the ENET->MSCR register and check if the MII_SPEED bits is 0x09.

Hope it can help you

XiangJun Rong

Re: MDC frequency generation issues

jautry — Sun, 09 Oct 2022 23:09:31 GMT

Ok if I set MSCR register to 0x112, I get .14us clock or about 7mhz. The ref_clk is measured at .02us or 50mhz (measured with a scope). I would expect to get 2.5mhz out. I have to set MSCR to 0x140 in order to get the 2.5mhz.

Re: MDC frequency generation issues

xiangjun_rong — Mon, 10 Oct 2022 02:05:31 GMT

Hi,

Pls try to use different MII_SPEED value and test the MDC clock frequency until it is 2.5MHz.

XiangJun Rong

Re: MDC frequency generation issues

jautry — Mon, 10 Oct 2022 18:14:25 GMT

??? That is what I did per my last entry. I had to put a value of 0x140 into the MSCR to get to 2.5mhz.