Hi Roland, I think the page I sent earlier has more info about MII, RMII, RGMII, etc that you need to know before attempting to do it. Let me put here for clarification:
"There are variants of the MII (GMII; RMII; SGMII; RGMII...) interface for connecting MACs to PHYs or MACs to MACs, in some of them there is a MAC or PHY role. The RGMII interface is a dual data rate (DDR) interface that consists of a transmit path and a receive path. Both paths have an independent clock, 4 data signals and a control signal. This means that in RGMII there is no PHY or MAC role, so no special support is needed for MAC-to-MAC connection as it is the case, being both ends in RGMII mode is enough for the communication to be carried out." Today I found a new page with more information and some details that probably will help you and others trying to do it, like clock shifting, otherwise it will not work: https://community.nxp.com/t5/i-MX-Processors/Direct-ETH-MAC-MII-to-MAC-MII-connection/m-p/1042795 So, if you didn't include the clock skew circuit as shown on this link, then you will need to use RMII. Best Regards, Alan On Fri, Mar 1, 2024 at 8:31 AM Roland <ning.rol...@mindpx.net> wrote: > @Alan, > > Thanks for the hints. > > From your message I will assume that this direct mode is not supported by > default, so I need to start looking into it. > > I already have a basic hardware setup includes a STM32F7 custom board and > an imx8m custom board, all prototypes. So it would be easier for me to > start from these platforms @Nathan. > > As the GPIO resources are always against us, RMII would be a more > realistic choice to me. > > In general level I have known it is possible, as I can find some > successful cases in other platforms. And I will not worry too much about > imx8m side which running Linux, which supports direct mode through RMII as > claimed. > I will be appreciated that if any Nuttx specific information/discussion > about this feature that you can also share? This may prevent me from > wasting time on something you may already explored. > > On hardware level, not sure if you can help to confirm my following > understanding, > > 1. MDIO pins are not mandatory, so these 2 pins are not used on current > prototypes in order to save GPIOs for other purposes. > 2. 50MHz Reference clock is provided from a shared crystal to feed into > both side. > > All the best, > /Roland > > > > On Mar 1, 2024, at 3:14 AM, Alan C. Assis <acas...@gmail.com> wrote: > > > > Hi Roland, > > > > We had a discussion about it a few months ago! > > > > We know it is possible, but nobody until now tried to do it. > > > > Basically you will need RMII support on both chips, I don't remember the > > details why MII will not work (or will be more difficult to work) > > > > There is a discussion about it here, maybe you can get more insights: > > > https://stackoverflow.com/questions/39503466/can-two-ethernet-mac-chips-be-connected-directly-without-going-thru-phy > > > > Best Regards, > > > > Alan > > > > > > On Thu, Feb 29, 2024 at 2:11 PM Roland <ning.rol...@mindpx.net> wrote: > > > >> Hi, > >> > >> I would like to directly connect a STM32F7 processor running Nuttx, to > an > >> external MCU (i.e., NXP imx8m) through RMII directly, without the need > for > >> PHY IC in between. > >> Is this supported by Nuttx? I checked into the documents but this direct > >> mode seems not been mentioned anywhere. > >> Can anyone please confirm if this is supported, or I have to change > >> something by myself? > >> > >> Thank you. > >> > >> /Roland > >> > >> > >
