"""
This module implements the communication protocol to switch the digital outputs
on a "dcttech" USB Relay.
Supported modules:
- USBRelay2 (and likely others)
Supported Functionality:
- Turn digital output on and off
"""
import usb.core
import usb.util
GET_REPORT = 0x1
SET_REPORT = 0x9
REPORT_TYPE_FEATURE = 3
[docs]class USBHIDRelay:
[docs] def __init__(self, **args):
self._dev = usb.core.find(**args)
if self._dev is None:
raise ValueError("Device not found")
if self._dev.is_kernel_driver_active(0):
self._dev.detach_kernel_driver(0)
[docs] def set_output(self, number, status):
assert 1 <= number <= 8
req = [0xFF if status else 0xFD, number]
self._dev.ctrl_transfer(
usb.util.CTRL_TYPE_CLASS | usb.util.CTRL_RECIPIENT_DEVICE | usb.util.ENDPOINT_OUT,
SET_REPORT,
(REPORT_TYPE_FEATURE << 8) | 0, # no report ID
0,
req, # payload
)
[docs] def get_output(self, number):
assert 1 <= number <= 8
resp = self._dev.ctrl_transfer(
usb.util.CTRL_TYPE_CLASS | usb.util.CTRL_RECIPIENT_DEVICE | usb.util.ENDPOINT_IN,
GET_REPORT,
(REPORT_TYPE_FEATURE << 8) | 0, # no report ID
0,
8, # size
)
return bool(resp[7] & (1 << (number-1)))
[docs] def __del__(self):
usb.util.release_interface(self._dev, 0)
[docs]def handle_set(busnum, devnum, number, status):
relay = USBHIDRelay(bus=busnum, address=devnum)
relay.set_output(number, status)
[docs]def handle_get(busnum, devnum, number):
relay = USBHIDRelay(bus=busnum, address=devnum)
return relay.get_output(number)
methods = {
'set': handle_set,
'get': handle_get,
}