Support connecting to ptys (not real serial ports) (ESPTOOL-493)

[manimathma]

When i try to use idf.py monitor/flash with serial pty it fails with ioctl error.

Start qemu using echr and strapmode

/tmp/qemu/build/qemu-system-xtensa -nographic -machine esp32 -drive file=flash_image.bin,if=mtd,format=raw -global driver=esp32.gpio,property=strap_mode,value=0x0f -echr 0x02 -serial pts

then try to flash image using idf.py flash
idf.py flash -p /dev/pts/7

and flash fails with following message

Failed to get PID of a device on /dev/pts/7, using standard reset sequence.

Traceback (most recent call last):
  File "/home/amanimu/Walnut_gcov/esp-dpk/external/esp-idf/components/esptool_py/esptool/esptool.py", line 5347, in <module>
    _main()
  File "/home/amanimu/Walnut_gcov/esp-dpk/external/esp-idf/components/esptool_py/esptool/esptool.py", line 5340, in _main
    main()
  File "/home/amanimu/Walnut_gcov/esp-dpk/external/esp-idf/components/esptool_py/esptool/esptool.py", line 4649, in main
    before=args.before)
  File "/home/amanimu/Walnut_gcov/esp-dpk/external/esp-idf/components/esptool_py/esptool/esptool.py", line 115, in get_default_connected_device
    _esp.connect(before, connect_attempts)
  File "/home/amanimu/Walnut_gcov/esp-dpk/external/esp-idf/components/esptool_py/esptool/esptool.py", line 664, in connect
    last_error = self._connect_attempt(mode=mode, usb_jtag_serial=usb_jtag_serial, extra_delay=extra_delay)
  File "/home/amanimu/Walnut_gcov/esp-dpk/external/esp-idf/components/esptool_py/esptool/esptool.py", line 614, in _connect_attempt
    self.bootloader_reset(usb_jtag_serial, extra_delay)
  File "/home/amanimu/Walnut_gcov/esp-dpk/external/esp-idf/components/esptool_py/esptool/esptool.py", line 592, in bootloader_reset
    self._setDTR(False)  # IO0=HIGH
  File "/home/amanimu/Walnut_gcov/esp-dpk/external/esp-idf/components/esptool_py/esptool/esptool.py", line 532, in _setDTR
    self._port.setDTR(state)
  File "/home/amanimu/.espressif/python_env/idf4.3_py3.6_env/lib/python3.6/site-packages/serial/serialutil.py", line 603, in setDTR
    self.dtr = value
  File "/home/amanimu/.espressif/python_env/idf4.3_py3.6_env/lib/python3.6/site-packages/serial/serialutil.py", line 473, in dtr
    self._update_dtr_state()
  File "/home/amanimu/.espressif/python_env/idf4.3_py3.6_env/lib/python3.6/site-packages/serial/serialposix.py", line 715, in _update_dtr_state
    fcntl.ioctl(self.fd, TIOCMBIC, TIOCM_DTR_str)
OSError: [Errno 25] Inappropriate ioctl for device
CMake Error at run_serial_tool.cmake:50 (message):
  /home/amanimu/.espressif/python_env/idf4.3_py3.6_env/bin/python
  /home/amanimu/Walnut_gcov/esp-dpk/external/esp-idf/components/esptool_py/esptool/esptool.py
  --chip esp32 failed

We get similar error for idf.py monitor as well.

We are using idf 4.3

[igrr]

I think the issue here is that esptool.py (or rather, pyserial library used by esptool.py) cannot work with /dev/pts instead of a serial port.
You can use a TCP port, though, which is supported both in qemu and in pyserial. Please see https://github.com/espressif/qemu/wiki#using-esptoolpy-and-espefusepy-to-interact-with-qemu for the instructions.

[manimathma]

@igrr Thanks for prompt feedback. We will look into the tcp option. It would be great if esptool could support pty. I was able to use latest pyserial module control pty. Not sure why esptool alone can't do it. Not a blocker or such. But good to have.

[igrr]

Probably this is because esptool expects to be able to reset the remote target using DTR and RTS handshaking lines, which are normally wired to GPIO0 and EN pins of the ESP. In case of the pty, an attempt to control DTR/RTS via the TIOCMBIC ioctl leads to an error.

esptool could ignore these errors (or disable DTR/RTS handling), but then the result would be no different from using a TCP port, where the handshaking lines (and thus resetting the remote target) aren't supported. So I don't see what pty support adds on top of the existing TCP socket support.

[manimathma]

Our team already has an infra on top of ttys to automatically run test. With TCP port, we would have to make significant change to make our testing infra to make it work with simulator.

Sorry if this question is dumb, is there a way we could start simulator with both tcp port and pts.

I tried that, but only first serial option works and i couldn't use the second serial port itself.

If we have a way to have both, then for flashing i can use tcp port and for running test i could use pts.

[igrr]

I've moved this issue into esptool repository, since the feature would have to be implemented here, not in QEMU.

The minimal implementation could be to catch "Inappropriate ioctl for device" error inside setDTR/setRTS functions. Or, detect that the port is a pty and warn/error out if hard reset (before or after flashing) is requested.