Fastest communication interface between two STM32F7's

[Maz D]

Posted on July 31, 2017 at 16:02

Hi,

I have a simple question but which causes me a little headache.

Does anyone know how I might interface two STM32F7 so that I might obtain the fastest communication between the two?

Something better than 10MBytes would be the best and 20MBytes excellent.

If my question needs more info do not hesitate to ask for clarification.

All help would be appreciated.

Thanks

#speed #interface #best #fastest #communication #stm32f7

[Maz D]

Posted on August 01, 2017 at 09:43

Both USB HS interfaces ( one on each MCU) are used for other purposes. The data from one gets shoveled to the other. And as said by Julien the quad SPI line on the F7 is master only.

[Maz D]

Posted on August 01, 2017 at 09:46

The space on the PCB is my main problem actualy. I am realy constrained. I dont realy have space left for other components.

[andy b]

Posted on August 01, 2017 at 18:13

Hi

Apparently nobody talked about connecting your stm32f7 with ethernet.Can achieve high speeds and with RMII interface you can do it with few MCU pins.Depending on the protocol you use if you do UDP you can transit data pretty fast.You only need to implement your own checksome/datacheck to make sure everything you've received is intact but if your lines stay on your PCB this may not be required if your hardware has the correct protections.You can have your main MCU as server and second one as client.Hope this helps-Andy

[Tesla DeLorean]

Posted on August 01, 2017 at 19:49

Can you flip the RX/TX pairs and connect them back-to-back without a PHY?

[andy b]

Posted on August 01, 2017 at 20:16

Not sure about this tried checking and the good old Goggles and haven't found a clear answer.But if needed just putting 2 PHY will probably work.They are some of the smaller chips out there so even tho he's clearly said he doesn't have much room left on his pcb he probably has enough for 2 tiny chips ,a few resistors and capacitors.He can probably do it in 1 1/2 square inches if not less.Your question certainly makes me want to try PHY less.I'll keep searching a bit to see if someone's done it before.

[andy b]

Posted on August 01, 2017 at 20:27

I have found someone that does it between an STM32 and a FPGA so it's probably possibe to do it between two STM32's(I'm guessing) Here is the link if any of you are interested it is actually really well explained how he manages to do it without any PHYs and which lines sneed to be switched in order for this to work: 

http://www.jsykora.info/2016/01/connecting-mcu-and-fpga-at-100mbits-using-ethernet-rmii-part-1/

 

-Andy

[S.Ma]

Posted on August 02, 2017 at 04:43

First question would be the bus length and capacitance, signal integrity. If both mcu are within 20cm, 40 mbps per spi should be doable with 160mhz sysclk with relatively simple sw stack. Ethernet interface, if available might be doable as well. A qspi mram bus shared and sw arbitrated could also be considered with sdio: reading can be done by hw memory mapping.

[Maz D]

Posted on August 02, 2017 at 14:38

It's also something that I looked into. Due to the SMI line one needs to use a PHY or a FPGA . Another issue for me is that the ethernet connections maximum baud rate is 100Mbit/s or about 12 MBytes/s without substracting overhead.

The SPI connection with 54MHz theoretical speed in master -master seems more straitforward to implement and could, if agregated, offer baudrates of up to 6.75 *2 MBytes/s without requiring external components or without too much indepth knowledge of the interface.

https://st-onlinetraining.s3.amazonaws.com/STM32F7-Peripheral_Serial_Peripheral_interface/index.html

 

[Maz D]

Posted on August 02, 2017 at 14:41

I agree as I think this is still the best method because it demands the least rework of libraries. I will go for this solution and tell you how it goes.

[Eugene Solo]

Posted on August 03, 2017 at 09:44

Don't listen to them. Use QSPI bus with one additional pin for direction handshaking (or even without that pin, use existing pins from QSPI itself of 'out-of-band' signalling)