![]() ![]() Overall I think you got the idea and maybe you even don't need an output GPIO line. With gpioget and gpioset it's currently impossible because the driver restores the state immediately after device node (of the GPIO controller) is closed. either you need deprecated sysfs interface to the GPIO chip or you have to run a thread or fork a process from your code to keep the context state correct. Let's assume the hardware state of the pin has been changed from 0 to 1: % echo 1 > /sys/kernel/debug/gpio-mockup/gpiochip2/2Ĭheck the state of the pin again: % gpioget 2 2įor the output part it's a bit complicated, i.e. (Note write-only attribute there) Now demo partĬheck first the current state of a pin (let's choose pin 2 of that virtual GPIO controller): % gpioget 2 2 NONE CH340R:No Connection, must be suspend 5. % ls -l /sys/kernel/debug/gpio-mockup/gpiochip2/ CH340R:Serial mode input setting, built-in pull-up resistor, SIR infrared serial interface when low, common serial interface when high CK0 OUT CH340T: clock output 1 NONE NONE NC. whatever you write there, the Linux stack will consider as a state of hardware: % mount -t debugfs none /sys/kernel/debug Through DebugFS you may see the lines as being on the hardware side, i.e. Line 2: "gpio-mockup-A-2" unused input active-high Line 1: "gpio-mockup-A-1" unused input active-high ![]() Line 0: "gpio-mockup-A-0" unused input active-high You create a virtual GPIO chip: % modprobe gpio-mockup gpio_mockup_ranges=-1,3 gpio_mockup_named_lines 4 PCS Loopback Plug Tester Fiber Optical Duplex Loop Ring Cable Adapter (LC-Line, Single Mode-UPC) 5.0 out of 5 stars. Luckily in the Linux kernel we have gpio-mockup (and new coming gpio-sim) which is used for testing GPIO library and APIs. 2-Pack Single Mode LC/UPC Fiber Optic Loopback Adapter Cable, Singlemode 9/125 Test Plug for Testing Applications. Is there anything that could be blocking their receive that I haven't tried? Once again, I'm assuming something is configured differently since the first port has expected behavior (other than the auto loopback I didn't expect), but I haven't found any rules applied to any of the ports.If there is no real hardware available to you, there is no such possibility without hacking a real kernel driver. ![]() I'm not sure why that would happen.Īfter testing the other ports that were showing 0 on transmit and receive, I noticed that I actually am seeing the transmit value increase, but they are unable to receive. So, I can cat that file any time before I run the python script, as many times as I want, but immediately after I run that Python, I can't cat the file, it just immediately returns with nothing. There's a few more serial ports, but they all have 0 tx and rx, and on port 03F8, the tx and tx increase when I send to the serial port ttyS0Īnother problem/symptom that could be related is that after I run the python script, I'm no longer able to cat /dev/ttys0 There is no change to this output when the echo command to the port is running with or without the cable connected.Ĭheck that the transmit and receive numbers change Output: /dev/ttyS0, UART: 16550A, Port: 0x03f8, IRQ: 4ĬTS and similar pins change when signal applied Finalized in 1987 (revision A finalized in 1992 1 ), the specification defines the cable between the DTE and DCE devices. If I run without sudo I get a blank line returned Currently known as TIA-530-A, but often called EIA-530, or RS-530, is a balanced serial interface standard that generally uses a 25-pin connector, originally created by the Telecommunications Industry Association. Output: Error I will have to copy in later. Output: crw-rw-, 1 user group 4, Date /dev/ttyS0 Like I said, I get the expected output from both tests, but I get the same output whether the cable is connected or not.Ĭhecking if interface is really a character device The same thing happens when I use the much shorter and simple serial test shown below Ser = serial.Serial(COM_PORT, BAUD_RATE, timeout=1, parity=serial.PARITY_NONE, rtscts=False, dsrdtr=False) In case it's useful information I'm using pySerial shown below (I had to type some of it from memory so I apologize if there are errors, but my question isn't about the code as much as it is how these ports actually work) import serial Is there some kind of software loopback that already exists for ports in Linux? I have something in python that tests the port, but I've found that the program returns the expected values even when my loopback isn't attached. Loopback will connect the RX to the TX in the chip internal side, which don't need to add external TTL-USB tool, that's why I confusing why you use the external TTL-USB, but you still use the internal loop back mode, you totally can use the SDK directly without the loopback, and if you want to use UART2, just change pins, and the UART number to UART2 and the interrupt service. I'm new to using serial ports, and I have a loopback cable for serial on a Centos 7 machine. ![]()
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