UART communication - Githubissues

m2oswald commented 5 years ago

Hi there. I am using the Hillcrest FSM300 board with an Arduino Mega and your code works perfectly. I was wondering if you have ever tried to communicate via UART instead of I2C? I tried converting the BNO080_2 code to talk to the FSM300 through the Mega's Serial1 connection, but have had no luck at all. Serial1.available never goes > 0, so I don't know whether I'm not sending the setup commands correctly or not listening correctly. I tried looking through Hillcrests' Nucleo code but that hasn't helped at all, and their tech support hasn't either.

Any help/advice you could give would be greatly appreciated, as I've been banging my head against the wall for a few days now and have gotten nowhere (except a headache).

Michael

jps2000 commented 5 years ago

Hi Michael I never tried that In Hillcrest data sheet there is a description of how to use the uart interface. it is meant for robot vacuum cleaners. Would try that to see if interface works. You need a 3v Uart of course. This is what the spec says 1.3.3.1 UART operation The UART is configured for 3Mkb/s, 8 data bits, 1 stop bit and no parity. The UART protocol relies on an idle line being ‘high’. A transmission is started with the assertion of a start bit (pulling the line low), followed by the data, LSB first. After the data segment is sent (in this case 8-bits), the line is pulled high (the stop signal) for a minimum number of bits (1 for the BNO08X) to indicate end of that segment. Bytes sent from the host to the BNO08X must be separated by at least 100us. Bytes sent from the BNO to the host have no extra spacing

I never heard about this 3Mkb/s? sanity check TX goes to RX and vice versa?

m2oswald commented 5 years ago

Thanks so much, I appreciate the quick reply. I actually just tried the UART-RVC mode, and that works. So that means that I'm able to read the comm port ok, my problem is that I'm not writing to it correctly (or, at least, not in a way that the BNO080 understands). I'm wrapping my SHTP messages in the UART 'framing bytes' as mentioned at the very end of 1.3.3.1 and detailed in Hillcrest's 1000-3535 document. I'm running at 3000000 baud (which seems way too high, but is specified everywhere so I'm just going with it). And I even tried swapping the RX and TX, just in case. Nothing.

As far as the serial comm details (pulling the line high/low and separating by a 100us pause) I'm making the assumption that the Arduino's Serial library is doing these things correctly. And I guess that since I'm able to read data in the UART-RVC mode, maybe that's true.

Thanks again for your help. It half works now. I'll go back to banging my head against the wall for awhile.

Michael

On Fri, Nov 30, 2018 at 1:01 PM Peter notifications@github.com wrote:

Hi Michael I never tried that In Hillcrest data sheet there is a description of how to use the uart interface. it is meant for robot vacuum cleaners. Would try that to see if interface works. You need a 3v Uart of course. This is what the spec says 1.3.3.1 UART operation The UART is configured for 3Mkb/s, 8 data bits, 1 stop bit and no parity. The UART protocol relies on an idle line being ‘high’. A transmission is started with the assertion of a start bit (pulling the line low), followed by the data, LSB first. After the data segment is sent (in this case 8-bits), the line is pulled high (the stop signal) for a minimum number of bits (1 for the BNO08X) to indicate end of that segment. Bytes sent from the host to the BNO08X must be separated by at least 100us. Bytes sent from the BNO to the host have no extra spacing

I never heard about this 3Mkb/s? sanity check TX goes to RX and vice versa?

— You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub https://github.com/jps2000/BNO080/issues/6#issuecomment-443196801, or mute the thread https://github.com/notifications/unsubscribe-auth/ArYSLLd-Yb32Q243hhyO640VJgZEUUuEks5u0SwPgaJpZM4Y7hT5 .

jps2000 commented 5 years ago

not sure but can the mega do this speed? After power on/ reset better wait for 600ms or longer Have you digested the SHTP transport protocol chapter 4?

ramiss commented 5 years ago

I commend you for trying this. Unfortunately others have confirmed the mega uart only handles at most 250,000 bps.

Are you just trying for science or do you really not have i2c/SPI available?

m2oswald commented 5 years ago

Of course, I was so focused on finding the problem with the FSM300 that I didn't even think about limitations on the Mega. Ok, well that's my answer then. And it explains why UART-RVC works - it communicates at 115200 baud.

Thank you for the help and advice, I really appreciate it.

Michael

On Fri, Nov 30, 2018 at 3:02 PM ramiss notifications@github.com wrote:

I commend you for trying this. Unfortunately others have confirmed the maga only handles at most 250,000 bps.

Are you just trying for science or do you really not have i2c available?

— You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub https://github.com/jps2000/BNO080/issues/6#issuecomment-443230290, or mute the thread https://github.com/notifications/unsubscribe-auth/ArYSLOAzey6udGV9ixlBkiLZdCEf_CeYks5u0UihgaJpZM4Y7hT5 .

m2oswald commented 5 years ago

Sorry, I forgot to respond to ramiss. For my application, the arduino and the sensor will be separated by 2-4 m, which I think is pushing it for reliable I2C. And this is going to be mounted on platform in a fairly remote location, so once it's in place it really needs to work because I can't go back in to change it.

jps2000 commented 5 years ago

That is not a distance that can not be made with I2C. Maybe the P82B715 is the guy for you https://www.nxp.com/products/analog/interfaces/ic-bus/ic-bus-repeaters-hubs-extenders:MC_41849 additionally you may use low capacitance cables known from audio electronics ( microphones etc). In Europe they are called "diode cable" like this https://www.conrad.at/de/diodenkabel-2-x-008-mm-schwarz-kabeltronik-640200800-meterware-486055.html These are just shielded cables with thick isolation and thin inner conductor. You can even try such a cable in your application without repeater just by reducing the pullups to minimum allowed. Pullups should be preferably equal on both sides. Minimum value is determined by the low level what the output stage can achieve at a certain current. 470 ohms should in fact be no problem. You can test your setup by adding small capacitors ( e.g. multiples of 47pF) between SCL & SDA to GND to see what you can sustain and what margin is left.

ramiss commented 5 years ago

I agree with Peter. I2C will be ok at 4M with shielded cables and pullups. You may have to reduce transmission rate, but on the whole it would be no less reliable than using serial. The I2C repeater should guarantee the distance.

m2oswald commented 5 years ago

My equipment is actually going to be underwater, off the coast of northern Scotland. So I'm limited in the cables that I can use as they will be exposed to seawater. The arduino is housed in a watertight enclosure, and the FSM300 will be potted and mounted on a adjustable platform a meter or two away. I did the calculations based on the capacitance of the cable I plan to use, and I think 2 m would be ok with small (1.2k) pull-up resistors on the SDA and SCL lines. But it just seems like there's more places something could go wrong with I2C compared to serial. I spoke with Hillcrest tech support and the FSM300 is stuck at 3Mbps for regular UART mode, so that's out. But I think the UART-RVC mode will be good enough for my purposes, and that only requires 115200 baud. Thanks again to both of you for all of your help and advice, I appreciate it.

jps2000 commented 5 years ago

Welcome. At any moment you can try the cable you intended to use with I2C bus and see what happen. With UART RVC the BNO080 is just spiiting data. So you can not do tare etc.