Unable to open serial port with mikepb's go-serial

Question

I try to communicate with a serial device using this package. I adopted the provided sample code to my needs as follows:

package main

import (
  "github.com/mikepb/go-serial"
  "log"
)

func main() {
  options := serial.RawOptions
  options.BitRate = 9600
  p, err := options.Open("/dev/cu.usbmodem641")
  if err != nil {
    log.Panic(err)
  }

  defer p.Close()

  buf := make([]byte, 1)
  if _, err := p.Read(buf); err != nil {
    log.Panic(err)
  } else {
    log.Println(buf)
  }
}

However, I am not able to open the serial port. An error is raised:

2018/09/22 21:50:24 The requested operation is not supported by this system or device
panic: The requested operation is not supported by this system or device

goroutine 1 [running]:
log.Panic(0xc000049f50, 0x1, 0x1)
  /usr/local/Cellar/go/1.11/libexec/src/log/log.go:326 +0xc0
main.main()
  /Users/Albert/go/src/serial-test/test.go:14 +0xda
exit status 2

How could I narrow this down? I am working on MacOS 10.10.5 with golang 1.11 from Homebrew. The serial device is an FTDI FT232 or an Atmega 16U2 on-board an Arduino (working with Arduino IDE).

---

Update due to comments:

I had a typo in my code. /dev/cu.usbmodem641 is actually /dev/cu.usbmodem411 which is available in device directory as ll /dev/cu.* shows:

crw-rw-rw-  1 root  wheel   17,   1 16 Sep 20:46 /dev/cu.Bluetooth-Incoming-Port
crw-rw-rw-  1 root  wheel   17,   3 16 Sep 20:46 /dev/cu.Bluetooth-Modem
crw-rw-rw-  1 root  wheel   17, 151 23 Sep 13:21 /dev/cu.usbmodem411

Go with go-serial package itself lists the device as well by using:

package main

import (
  "fmt"
  "log"
  "github.com/mikepb/go-serial"
)

func main() {
  portInfo, err := serial.ListPorts()
  if err != nil {
    log.Panic(err)
  }
  for _, info := range portInfo {
    fmt.Println(info.Name())
  }
}

Giving the following output:

$ go run list_serial.go 
/dev/cu.Bluetooth-Incoming-Port
/dev/cu.Bluetooth-Modem
/dev/cu.usbmodem411

I fixed the typo in the snipped I provided in my question above and tried again which leads to an invalid arguments error:

$ go run test.go 
2018/09/23 13:33:32 Invalid arguments were passed to the function
panic: Invalid arguments were passed to the function

goroutine 1 [running]:
log.Panic(0xc000049f50, 0x1, 0x1)
    /usr/local/Cellar/go/1.11/libexec/src/log/log.go:326 +0xc0
main.main()
    /Users/Albert/go/src/go-echo-vue/test.go:13 +0xda
exit status 2

I double-checked everything, found no additional error in my code and ran again. This time getting another error:

$ go run test.go 
2018/09/23 13:37:26 The requested operation is not supported by this system or device
panic: The requested operation is not supported by this system or device

goroutine 1 [running]:
log.Panic(0xc000044f50, 0x1, 0x1)
    /usr/local/Cellar/go/1.11/libexec/src/log/log.go:326 +0xc0
main.main()
    /Users/Albert/go/src/go-echo-vue/test.go:13 +0xda
exit status 2    

Remark: Serial ports on macOS have two interfaces to the device itself. One is the tty.*, the other is cu.*. For a short explanation see this SO answer. I was not able to get the Go code running with either of those interfaces raising same errors as stated before.