>> I am confused as to what your actual hardware configuration is, with
respect to the "serial communications."
The actual hardware used in the final project with the i2c connectors
soldered on to a prototyping cape looks like this:
I have repeated the exact same fault on this:
>> Are you using a COM port in Windows to talk to a USB to serial cable,
which is talking to a hardware serial port in the BBB?
I plugged the micro USB port on the BBB into my USB hub. The USB hub is
currently attached to a windows PC but the same fault happens when the USB
cable is plugged into my mac book running OSX.
Within a minute of the BBB being plugged in an extra COM port is added in
windows. I connect to the com port with Termite (terminal program), ZOC7
(terminal program) or pyserial (the python serial library).
When I connect to the COM port I can login and get a shell. I ran some
relevant commands in the shell so you can see the results.
root@beaglebone:/dev# w
20:57:21 up 6:52, 1 user, load average: 0.02, 0.06, 0.05
USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT
root ttyGS0 14Nov15 1.00s 0.97s 0.02s w
root@beaglebone:/dev# who
root ttyGS0 2015-11-14 00:15
root@beaglebone:/dev# tty
/dev/ttyGS0
root@beaglebone:/dev# whoami
root
root@beaglebone:/dev# ls
alarm log_system ram11 tty16 tty44 ubi_ctrl
ashmem loop0 ram12 tty17 tty45 uinput
audio loop1 ram13 tty18 tty46 urandom
autofs loop2 ram14 tty19 tty47 usbmon0
binder loop3 ram15 tty2 tty48 usbmon1
block loop4 ram2 tty20 tty49 usbmon2
btrfs-control loop5 ram3 tty21 tty5 vcs
bus loop6 ram4 tty22 tty50 vcs1
char loop7 ram5 tty23 tty51 vcs2
console loop-control ram6 tty24 tty52 vcs3
core mapper ram7 tty25 tty53 vcs4
cpu_dma_latency mem ram8 tty26 tty54 vcs5
disk mixer ram9 tty27 tty55 vcs6
dri mmcblk0 random tty28 tty56 vcs7
dsp mmcblk0boot0 root tty29 tty57 vcsa
fb0 mmcblk0boot1 rtc0 tty3 tty58 vcsa1
fd mmcblk0p1 shm tty30 tty59 vcsa2
full mmcblk0p2 snd tty31 tty6 vcsa3
fuse mqueue sndstat tty32 tty60 vcsa4
hwrng net stderr tty33 tty61 vcsa5
i2c-0 network_latency stdin tty34 tty62 vcsa6
i2c-1 network_throughput stdout tty35 tty63 vcsa7
initctl null tty tty36 tty7 watchdog
input ppp tty0 tty37 tty8 watchdog0
kmem psaux tty1 tty38 tty9 xconsole
kmsg ptmx tty10 tty39 ttyGS0 zero
log ptp0 tty11 tty4 ttyO0
log_events pts tty12 tty40 ttyS0
logibone_mem ram0 tty13 tty41 ttyS1
log_main ram1 tty14 tty42 ttyS2
log_radio ram10 tty15 tty43 ttyS3
>> So, you've actually delved further into using the UARTs on this platform
than I ever have.
I have also come to suspect that there are no hardware UARTS involved. I
believe that the serial line is being emulated.
>> Anyway, my first instinct wants to say baud rate is involved somehow.
On the PC side I can set the baudrate to any number. The data rate and the
error rate appear to be unaffected. For example:
x = serial.Serial('COM10', baudrate=10)
x = serial.Serial('COM10', baudrate=9600)
x = serial.Serial('COM10', baudrate=100_000_000_000)
I have also set the baud rate with Termite 3.1 to demonstrate that it is
not a bug in the python serial library.
On the BBB end the speed is always reported as 9600. Some commands to
change the speed succeed and others fail but the reported speed is
unchanged.
root@beaglebone:/dev# stty ispeed 7200
root@beaglebone:/dev# stty
speed 9600 baud; line = 0;
root@beaglebone:/dev# stty ispeed 14400
root@beaglebone:/dev# stty
speed 9600 baud; line = 0;
root@beaglebone:/dev# stty ispeed 2400
stty: standard input: unable to perform all requested operations
root@beaglebone:/dev# stty
speed 9600 baud; line = 0;
I will finish replying to everyone tomorrow. It is getting late where I am.
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