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Demonstrating the BeagleBone Black's Kernel driver working in RS485 mode with Michael Musset's gpio RTS patch
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import serial, fcntl, struct, time | |
ser = serial.Serial( | |
port='/dev/ttyO4', | |
baudrate=9600, | |
timeout=1, | |
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-by-Michael-Musset.patch#L30) | |
SER_RS485_ENABLED = (1 << 0) | |
SER_RS485_RTS_ON_SEND = (1 << 1) | |
SER_RS485_RTS_AFTER_SEND = (1 << 2) | |
SER_RS485_RTS_BEFORE_SEND = (1 << 3) | |
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 | |
# With this configuration the GPIO pin will be high when transmitting and low | |
# when not | |
# If SER_RS485_RTS_ON_SEND and SER_RS485_RTS_AFTER_SEND flags are included the | |
# RE/DE signal will be inverted, i.e. low while transmitting | |
# 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=ser.fileno() | |
fcntl.ioctl(fd, TIOCSRS485, serial_rs485) | |
# Send some bytes: | |
# GPIO1_16 should be low here | |
time.sleep(0.2) | |
# GPIO1_16 should be high while this is being transmitted: | |
ser.write("RS485 test") | |
# GPIO1_16 should be low again after transmitting | |
time.sleep(0.2) | |
ser.close() |
Is this patch merged with the latest debian image?
I tried on my bb and it cannot write.
I have the same problem.
Have you solved this problem?
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Is this patch merged with the latest debian image?
I tried on my bb and it cannot write.