Issues with Odrive native interface over USB (C++)

Support
1

Hi,

I am trying to get Odrive working with C++ over USB.
I am using libusb to facilitate the communication between my machine and Odrive.

I am first trying to retrieve the JSON endpoints definition from within the USB itself.
Per the documentation I am creating my request like so and sending it to endpoint 0:

81 0 0 80 40 0 0 0 0 0 1 0

I can then get a response from the Odrive and then try to retrieve the rest of the JSON. So I will send another request like so:

82 0 0 80 40 0 0 0 0 0 1 0

I am getting a response from the Odrive but it is always the exact same and so I am not sure what is going wrong here. The response I am getting is (minus the first 2 bytes):

5b 7b 22 6e 61 6d 65 22 3a 22 22 2c 22 69 64 22 3a 30 2c 22 74 79 70 65 22 3a 22 6a 73 6f 6e 22 2c 22 61 63 63 65 73 73 22 3a 22 72 22 7d 2c 7b 22 6e 61 6d 65 22 3a 22 65 72 72 6f 72

Which decodes to:

[{"name":"","id":0,"type":"json","access":"r"},{"name":"error

But I am not sure what I am doing wrong here. Any help would be appreciated!

2

The payload of your request needs to contain the number of bytes you already received. If you always set it to 0, you always get the beginning of the json :wink:

Something like this:

	do {
		serialize(send_payload, (int)received_json.size());
		endpoint_request(0, receive_payload, send_payload, true, 64, false);
		send_payload.clear();
		for (u8 byte : receive_payload) {
			received_json.push_back(byte);
			//printf("%c", byte);
			//fflush(stdout);
		}
	} while (receive_payload.size());

BTW It’s strange that you receive anything at all. Usually the last two bytes should contain the firmware crc.

3

Awesome that was the missing piece of the puzzle thanks for your help!
The CRC for endpoint 0 is the protocol version but for all other endpoints it’s the CRC of the JSON.
Do you know how large the JSON is currently? I am trying to ensure I did everything properly.

4

No, but you can keep requesting data until nothing comes back. See my code above

5

Ok so everything is working now thanks a lot for your help.
I’ve moved on to trying to use other endpoints. I started off with endpoint 5 to try to retrieve the SN.
The issue is I am not 100% sure if my JSON CRC is correct.

In the documentation it takes you to a sample calculator that you can use to calculate the CRC16.

I am not clear if the initial value should be 0x0001 or 0x1337 but neither of the CRCs generated from the retrieved JSON seem to work (0x23F7 or 0xD67B).

I am querying endpoint 5 like so but keep receiving a timeout response:

70 3 5 80 8 0 0 0 0 0 f7 23

Any advice would be great :slight_smile:

6

Ok I learned from another forum that the CRC should be 0xD271 but I am not sure what the difference is in the calculation since I used the same algo from the documentation.

7

You can send a request with endpoint 0 and 0xffffffff in the payload. You then receive a 32-bit number with the crc being the upper 16 bits. Don’t know if this is official behavior, but it works :wink: