Reverse-engineered pyusb code to read from a renesas RL78G13 promotion board. It uses some random MCU as a debug/programmer tool and a USB->serial device. Windows drivers only. All of the ctrl_transfers were sniffed using wireshark inbetween a windows VM.

RL78_serial_remote.py

import usb.core
import usb.util
import sys
from commands import getstatusoutput
import json

# find our device
dev = usb.core.find(idVendor=0x045b, idProduct=0x0212)
# was it found?
if dev is None:
    raise ValueError('Device not found')
dev.set_configuration()
# get an endpoint instance
cfg = dev.get_active_configuration()
interface_number = cfg[(0,0)].bInterfaceNumber
alternate_setting = usb.control.get_interface(dev,interface_number)
intf = usb.util.find_descriptor(
    cfg, bInterfaceNumber = interface_number,
    bAlternateSetting = alternate_setting
)

ep = usb.util.find_descriptor(
    intf,
    # match the first OUT endpoint
    custom_match = \
    lambda e: \
        usb.util.endpoint_direction(e.bEndpointAddress) == \
        usb.util.ENDPOINT_IN
)

assert ep is not None
# open serial port and set parameters (
dev.ctrl_transfer(0x40, 11, 0x0000, 0, '\x03\x01')
dev.ctrl_transfer(0x40, 11, 0x0000, 0, '\x01\x03')
dev.ctrl_transfer(0x40, 11, 0x0000, 0, '\x00\x80\x25\x00\x00\x01')
dev.ctrl_transfer(0x40, 11, 0x0000, 0, '\x04\x00\x00')
dev.ctrl_transfer(0x40, 11, 0x0000, 0, '\x01\x03')
dev.ctrl_transfer(0x40, 11, 0x0000, 0, '\x01\x03')
dev.ctrl_transfer(0x40, 11, 0x0000, 0, '\x00\x80\x25\x00\x00\x01')
dev.ctrl_transfer(0x40, 11, 0x0000, 0, '\x04\x00\x00')
dev.ctrl_transfer(0x40, 11, 0x0000, 0, '\x02\x11\x13')
dev.ctrl_transfer(0x40, 11, 0x0000, 0, '\x04\x00\x00')
dev.ctrl_transfer(0x40, 11, 0x0000, 0, '\x00\x80\x25\x00\x00\x01')
dev.ctrl_transfer(0x40, 11, 0x0000, 0, '\x04\x00\x00')

def changeVolume(volume):
    code,output =  getstatusoutput('pactl set-sink-volume 0 -- '+str(volume)+'%')
    sys.stdout.write(str(volume)+'%                \r')
    sys.stdout.flush()
    if code != 0:
        print "Error changing volume: "+output

def buttonPress(button):
    code = 0
    output = ''
    if button == 1:
        code,output = getstatusoutput('xdotool key XF86AudioNext')
        sys.stdout.write('next      \r')
        sys.stdout.flush()
    elif button == 2:
        code,output = getstatusoutput('xdotool key XF86AudioPlay')
        sys.stdout.write('play/pause\r')
        sys.stdout.flush()
    elif button == 3:
        code,output = getstatusoutput('xdotool key XF86AudioPrev')
        sys.stdout.write('prev      \r')
        sys.stdout.flush()
    if code != 0:
        print "Error pressing key: "+output

def parseLine(line):
    jdata = json.loads(line)
    if 'volume' in jdata:
        changeVolume(jdata['volume'])
    elif 'buttonDown' in jdata:
        buttonPress(jdata['buttonDown'])

print "Reading volume data from remote:"
reading = True
line = ''
while(reading):
    try:
        newchar = chr(dev.read(ep.bEndpointAddress, 1, intf, 5000)[0])
        line += newchar
        if newchar == '\n' and line[-2] == '\r':
            parseLine(line.rstrip())
            #print line.rstrip()
            #changeVolume(line.split(',')[0])
            line = ''
    except KeyboardInterrupt:
        reading = False
        #let device know we're closing the port
        dev.ctrl_transfer(0x40, 11, 0x0000, 0, '\x03\x00')
        print "Port Closed."
    except usb.core.USBError as e:
        #on a USB timeout (err 110), continue, otherwise, close
        if e.errno != 110:
            print e
            reading = False
            #let device know we're closing the port
            dev.ctrl_transfer(0x40, 11, 0x0000, 0, '\x03\x00')
            print "USB error, Port Closed."