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Can communication of nano

2022-07-05 18:03:00 【Luo Xiaohei has a good war record】

I bought raspberry pie with light snow SPI turn CAN. Now it's used in jetson nano On . I saw that the chips of the two modules are the same , The pins are all right , So I'm going to give this module to nano do can signal communication .

Have CAN function , Use SPI Interface CAN controller MCP2515, With transceiver SN65HVD230. Microchip Of MCP2515 Is a CAN Protocol controller , Fully support CAN V2.0B The technical specification . The device can send and receive standard and extended data frames as well as remote frames . MCP2515 The built-in two acceptance mask registers and six acceptance filter registers can filter out unwanted messages . CAN The output pin of the controller Tx Receive SN65HVD230 The data of
Input end D, This can be CAN The data sent by the node is transferred to CAN In the network ; and CAN The receiving pin of the controller Rx and SN65HVD230 The data output of R Connected to a , For receiving data .
I bought it for raspberry pie can Expansion board

In short, start the installation

Specifically for nano It's done can Communication adapter board
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minicom External hardware devices can be controlled through serial port . Suitable in linux Manage embedded devices through HyperTerminal . It can also be used minicom On the outside Modem Control .
linux hyper terminal minicom How to use
minicom Is a serial terminal debugging tool

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Use /etc/modules-load.d/ To configure which modules are loaded when the system starts
Linux Module loading process and how to make the system automatically load modules after startup

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Follow the web tutorial steps , You can see our nano Of spi1 Pin and mine can On module spi Pins correspond to

【 acutely Restart failed after setting , Now the screen has been black , You can only re burn the image . After re burning and re operating, the tutorial is no problem , But the module pin and baud rate on my side don't match 】

There are several problems after installation

I bought raspberry pie with light snow SPI turn can, That module sets the interrupt output pin to nano Of 20 Position of pin No , I should change the module pin setting to 26 Pin No . But look nano Of SPI turn can The module of is also to set the position of the interrupt pin randomly . Maybe it doesn't matter if you change this .
The baud rate is not right
The extracted code file is only readable

#  Written by the merchant nano Of cantest.py  The test routine will send 1-8
#!/usr/bin/env python
# -*- coding: utf-8 -*-

import MCP2515
import time

print("--------------------------------------------------------")
# try:
# This setup is referred to CAN SPI click mounted on flip n click device slot A 
can = MCP2515.MCP2515()
print("init...")
can.Init()
print("send data...")
data = [1, 2, 3, 4, 5, 6, 7, 8]
can.Send(data, len(data))

readbuf = []
# while(1):
while(1):
	readbuf = can.Receive()
	print(readbuf)
	time.sleep(0.5)

print("--------------------------------------------------------")
# except Exception as e:
    # print(e)

About file permissions , I learned from brother bird

sudo chmod 777 -R Folder name /
This sentence opens all permissions

0(0+0+0)- No authority .
1(0+0+1)- Only execute permissions .
2(0+2+0)- Write permission only .
3(0+2+1)- Write and execute permissions .
4(4+0+0)- Read only permission .
5(4+0+1)- Read and execute permissions .
6(4+2+0)- read-write permission .
7(4+2+1)- Read 、 Write and execute permissions .

Usually we use Vim edit Shell After batch processing of documents , File permissions are usually rw-rw-r–（644）, that , If you want to make the file executable , And don't let anyone else modify this file , Only the permission of this file should be rwxr-xr-x（755） that will do .

chmod 755 Set the user's permission to ：
1. The file owner can read, write, and execute
2. Other users belonging to the same user group as the file owner can read and execute
3. Other user groups can read and execute

can Baud rate

MCP2515 Baud rate configuration
Because my module is 12M Crystal oscillator , The default in the program 8M Crystal oscillator , Therefore, it is necessary to recalculate the proportion of each communication stage according to the manual , Just refer to the blog above .
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The calculation process is complicated , It still needs a little experience . Tell the truth , If you have that time to understand my above calculation process , It's better to read the blog and deduce by yourself .

What we need to know is 500Kbps Is the corresponding 2us Of Tbit. from 1/2us obtain . In the same way 250Kbps Is the need to 4us,125Kbps by 8us

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【 Yes, of course , I didn't test one by one 】

If you change these two places, you can communicate 【 Connect the hardware first 】

So it really doesn't matter about the pin , I'm using 29 No. pin is output as an interrupt

Think about sending information

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The merchant is set like this Only one was made send function . If you want to send extended frames, you can only write them yourself .

The appended drawings

nano Corresponding pin interface of

This is the default pin function when nothing is set
Yes , This is my nano Corresponding pin interface of
nano Another more detailed table of , It is the corresponding pin that can be set to open .
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