Get RS485 on a BeagleBoneGreen + Waveshare CAN RS485 CAPE up and running

BeagleBoneGreen RS485.py

import serial, fcntl, struct

#inspired by http://inspire.logicsupply.com/2014/09/beaglebone-rs-485-communication.html

#enable ttyO4 by editing /boot/uEnv.txt: 
#cape_enable=capemgr.enable_partno=BB-UART4

# RX and TX Jumpers on the Waveshare Cape are set to UART4
# A jumper wire is connected from P9_15 to RSE (middle pin of the three)

s = serial.Serial(
    port="/dev/ttyO4",
    baudrate=9600,
    parity=serial.PARITY_NONE,
    stopbits=serial.STOPBITS_ONE,
    bytesize=serial.EIGHTBITS
)
# Standard Linux RS485 ioctl:
TIOCSRS485 = 0x542F
# define serial_rs485 struct per Michael Musset's patch that adds gpio RE/DE control:
# (https://github.com/RobertCNelson/bb-kernel/blob/am33x-v3.8/patches/fixes/0007-omap-RS485-support 
SER_RS485_ENABLED         = (1 << 0)
SER_RS485_USE_GPIO        = (1 << 5)
# Enable RS485 mode using a GPIO pin to control RE/DE:  
RS485_FLAGS = SER_RS485_ENABLED | SER_RS485_USE_GPIO 
# The GPIO pin to use, using the Kernel numbering: 
RS485_RTS_GPIO_PIN = 48 # GPIO1_16 -> GPIO(1)_(16) = (1)*32+(16) = 48
# Pack the config into 8 consecutive unsigned 32-bit values:
# (per  struct serial_rs485 in patched serial.h)
serial_rs485 = struct.pack('IIIIIIII', 
                           RS485_FLAGS,        # config flags
                           0,                  # delay in us before send
                           0,                  # delay in us after send
                           RS485_RTS_GPIO_PIN, # the pin number used for DE/RE
                           0, 0, 0, 0          # padding - space for more values 
                           )
# Apply the ioctl to the open ttyO4 file descriptor: 
fd=s.fileno()
fcntl.ioctl(fd, TIOCSRS485, serial_rs485)

s.write("Hi there!")

while True:
    res = s.readline()
    print(res)