I have two Jetson Nano devices that need to exchange data over SPI protocol. It is my first and only project with Jetson Nano, so I am completely new to the SPI or anything regarding low-level coding.
In the project, I want to use Daisy Chain to communicate, for starters I have used only two devices to test the data communication between them.
Using the following link on page 4, I made one a slave. https://www.nxp.com/files-static/training_pdf/26821_68HC08_SPI_WBT.pdf What it says is that in order to select one device as a slave you need to connect SS to ground to make it low. So I have connected pin 24 (SPI_1_CS0) to pin 20 which is ground. For the master, I have put pin 24 (SPI_1_CS0) to pin 2 (5.0 VDC). I intended to set it high for it to become the master.
I have used /opt/nvidia/jetson-io/jetson-io.py to configure the pins. After running sudo modprobe spidev the pins were configured.
Output of ls /dev/spi* is
/dev/spidev0.0 /dev/spidev0.1 /dev/spidev1.0 /dev/spidev1.1
After running the following code on the slave I received useless data. Since slave mode should have been activated, I should not be able to read data unless Master is sending some.
import spidev
import time
spi = spidev.SpiDev()
spi.open(0,0)
spi.max_speed_hz = 250000
def read_spi(channel):
spidata = spi.xfer2([0,(8+channel)<<4,0])
return ((spidata[1] & 3) << 8) + spidata[2]
def readData():
spidata = spi.readbytes(8)
return spidata
try:
while True:
#channelData = read_spi(0)
channelData = readData()
print (channelData)
time.sleep(.1)
except KeyboardInterrupt:
spi.close()
channelData can be received with the other function. But it does not make the result any different.
[20, 206, 54, 93, 19, 151, 211, 199]
[84, 10, 89, 184, 126, 82, 49, 78]
[189, 32, 110, 143, 231, 226, 76, 116]
[102, 56, 174, 123, 186, 145, 148, 161]
[105, 254, 152, 155, 88, 147, 191, 174]
[38, 221, 219, 179, 161, 102, 107, 31]
[101, 141, 98, 80, 20, 254, 25, 50]
[88, 0, 0, 44, 197, 73, 32, 49]
[107, 60, 44, 230, 91, 56, 172, 4]
[21, 156, 120, 165, 99, 137, 245, 204]
[15, 34, 164, 215, 255, 187, 34, 86]
[18, 215, 67, 227, 234, 1, 237, 142]
[71, 124, 36, 238, 86, 240, 105, 189]
[29, 27, 63, 232, 239, 40, 189, 61]
[5, 217, 209, 14, 96, 24, 181, 97]
[158, 121, 125, 93, 224, 125, 97, 129]
[75, 92, 95, 183, 47, 14, 111, 164]
Do I need more configuration to be done if I want to make one a slave or am I doing something wrong with the coding?
Any links or code example is appreciated.
Do you use Nvidia Jetson Nano custom board? Or custom board from other vendor? If you are using Nano devkit, please see the pin out below:
enter image description here
Picture is from this website.
spidev node location correction.
There are 2 SPI channels: SPI0 and SPI1. Interesting thing is SPI0 is located at /dev/spidev1 and SPI1 is at /dev/spidev2.x. Please see their device tree setting. Depends on how you wire SPI, if you are using SPI0 and CS/SS is connected to Pin24, use /dev/spidev1.0; if CS/SS is connected pin 26, use /dev/spidev1.1 instead.
device tree correction
Do you have a chance to modify your device tree? If you are certain of the wire connection correctness , then check device tree setting. As I know, Jetson Nano is not allowed to change SPI slave by any command. The only way is tweak the device tree.
I found a possible solution on github. See here