Measuring film camera shutter speed with Beaglebone Black

Here is a simple circuit utilizing the ADC input on Beaglebone Black to measure camera shutter speed.

A photoresistor is used to detect the light when shutter open, and hence changing the values read by ADC pin P9_40.  The push button is used to trigger the Python script to start reading the ADC input.


Testing on breadboard and the final build on through-hole board:

Note that this is by no mean an accurate measure of absolute shutter speed.  The response time (rise/fall) of photoresistor will affect the result (see the graph below).  Nevertheless, it is useful to compare different shutter speeds.

Source code is available on Github.

Quick start:

git clone https://github.com/kitsook/bbb-adc-measure
cd bbb-adc-measure
python3 -m venv venv
. venv/bin/activate
pip install -r requirements.txt
python adc-measure.py -t 10 > result.csv

Plot the output using gnuplot:

gnuplot
set mxtics 10
set grid
plot 'result.csv' with lines

Here is an example output of measuring 1/15 and 1/8 shutter speeds of my Pentax MX.

openSUSE Tumbleweed boot problem

After recent update (20180502) of openSUSE Tumbleweed, my machine failed to boot.  A quick check in the dracut emergency shell seems to indicate that somehow the root volume is mounted as /kdump/mnt0 and so cannot be mounted as root again.

Here is a quick fix.

Boot the system with LiveCD or any emergency tool.  Mount the Tumbleweed system (here I mounted it under /mnt/temp).  Go to the boot directory and find the initrd file.  We are going to extract and modify the fstab inside.

cd /mnt/temp/boot
mkdir initrd-mod
cd initrd-mod
/usr/lib/dracut/skipcpio ../initrd > initrd.xz
xz -d initrd.xz
cpio -idv < initrd
cd etc
# edit the fstab file, comment out the mount of /kdump/mnt0
vi fstab

Now, repackage the initrd file

cd /mnt/temp/boot/initrd-mod
find . 2>/dev/null | cpio --quiet -c -o | xz -9 --format=lzma >"../initrd-mod.img"
chmod go-r ../initrd-mod.img

The original boot/initrd should be a symbolic link to the current kernel version.  Remove it and point it to the modified initrd

cd /mnt/temp/boot
rm initrd
ln -s initrd-mod.img initrd
# Depends on your setup, you probably also need to
# backup and link specific kernel version of initrd. e.g.
# mv initrd-4.16.6-1-default initrd-4.16.6-1-default.bak
# ln -s initrd-mod.img initrd-4.16.6-1-default

Sync, umount, and reboot.  There will be error messages saying /kdump/mnt0 can't be mounted but at least the system can boot up.

SSL connections with RTL8710

If you tried to compile any SSL example (e.g. WiFiSSLClient) that comes with Ameba Arduino, you will probably get an error saying "RTL8710 do not support SSL".

Some people say it is because RTL8710 is not powerful enough (!?) to handle SSL.  But in fact, you edit the gcc linker blacklist file to get around it.  On Linux, the file is probably at

~/.arduino15/packages/realtek/hardware/ameba/2.0.4/variants/rtl8710/linker_scripts/gcc/symbol_black_list.txt

The original file contains:

rom_ssl_ram_map RTL8710 do not support SSL
analogReadResolution RTL8710 do not support ADC
analogRead RTL8710 do not support ADC

You can see that the RAM table referenced by SSL ROM is being blacklisted.  Make a backup of the file and delete the first line.

Tried to compile WiFiSSLClient and it work probably on my RTL8710.

Sony SRS-XB30 and WH-H800 supported codecs

For reference, here is the negotiation traffic captured when connecting to a Sony SRS-XB30 bluetooth speaker.

localhost:~> sudo hcidump avdtp
HCI sniffer - Bluetooth packet analyzer ver 5.49
device: hci0 snap_len: 1500 filter: 0x400
< AVDTP(s): Discover cmd: transaction 14 nsp 0x00
> AVDTP(s): Discover rsp: transaction 14 nsp 0x00
    ACP SEID 1 - Audio Sink
    ACP SEID 2 - Audio Sink
    ACP SEID 3 - Audio Sink
< AVDTP(s): All Capabilities cmd: transaction 15 nsp 0x00
    ACP SEID 1
> AVDTP(s): All Capabilities rsp: transaction 15 nsp 0x00
    Media Transport
    Media Codec - SBC
      16kHz 32kHz 44.1kHz 48kHz 
      Mono DualChannel Stereo JointStereo 
      4 8 12 16 Blocks
      4 8 Subbands
      SNR Loudness 
      Bitpool Range 2-53
    Content Protection
      02 00 
    Delay Reporting
< AVDTP(s): All Capabilities cmd: transaction 0 nsp 0x00
    ACP SEID 2
> AVDTP(s): All Capabilities rsp: transaction 0 nsp 0x00
    Media Transport
    Media Codec - MPEG-2,4 AAC
      MPEG-2 AAC LC 
      44.1kHz 48kHz 
      1 2 Channels
      0bps VBR
    Content Protection
      02 00 
    Delay Reporting
< AVDTP(s): All Capabilities cmd: transaction 1 nsp 0x00
    ACP SEID 3
> AVDTP(s): All Capabilities rsp: transaction 1 nsp 0x00
    Media Transport
    Media Codec - non-A2DP (LDAC)
      3C 07 
    Content Protection
      02 00 
    Delay Reporting
< AVDTP(s): Set config cmd: transaction 2 nsp 0x00
    ACP SEID 1 - INT SEID 1
    Media Transport
    Media Codec - SBC
      44.1kHz 
      JointStereo 
      16 Blocks
      8 Subbands
      Loudness 
      Bitpool Range 2-53
> AVDTP(s): Set config rsp: transaction 2 nsp 0x00
> AVDTP(s): Delay Report cmd: transaction 0 nsp 0x00
    ACP SEID 1 delay 240.0ms
< AVDTP(s): Open cmd: transaction 3 nsp 0x00
    ACP SEID 1
< AVDTP(s): Delay Report rsp: transaction 0 nsp 0x00
> AVDTP(s): Open rsp: transaction 3 nsp 0x00

By comparison, here is info when connecting a Sony WH-H800 Wireless Headphones:

localhost:~> sudo hcidump avdtp
HCI sniffer - Bluetooth packet analyzer ver 5.49
device: hci0 snap_len: 1500 filter: 0x400
< AVDTP(s): Discover cmd: transaction 8 nsp 0x00
> AVDTP(s): Discover rsp: transaction 8 nsp 0x00
    ACP SEID 1 - Audio Sink
    ACP SEID 5 - Audio Sink
    ACP SEID 6 - Audio Sink
    ACP SEID 3 - Audio Sink
    ACP SEID 2 - Audio Sink
< AVDTP(s): All Capabilities cmd: transaction 9 nsp 0x00
    ACP SEID 1
> AVDTP(s): All Capabilities rsp: transaction 9 nsp 0x00
    Media Transport
    Media Codec - SBC
      44.1kHz 48kHz 
      Mono DualChannel Stereo JointStereo 
      4 8 12 16 Blocks
      4 8 Subbands
      SNR Loudness 
      Bitpool Range 2-53
    Content Protection
      02 00 
    Delay Reporting
< AVDTP(s): All Capabilities cmd: transaction 10 nsp 0x00
    ACP SEID 5
> AVDTP(s): All Capabilities rsp: transaction 10 nsp 0x00
    Media Transport
    Media Codec - non-A2DP (LDAC)
      3C 07 
    Content Protection
      02 00 
    Delay Reporting
< AVDTP(s): All Capabilities cmd: transaction 11 nsp 0x00
    ACP SEID 6
> AVDTP(s): All Capabilities rsp: transaction 11 nsp 0x00
    Media Transport
    Media Codec - non-A2DP (Unknown)
      32 00 00 00 00 
    Content Protection
      02 00 
    Delay Reporting
< AVDTP(s): All Capabilities cmd: transaction 12 nsp 0x00
    ACP SEID 3
> AVDTP(s): All Capabilities rsp: transaction 12 nsp 0x00
    Media Transport
    Media Codec - non-A2DP (aptX)
      44.1kHz 48kHz 
      Stereo 
    Content Protection
      02 00 
    Delay Reporting
< AVDTP(s): All Capabilities cmd: transaction 13 nsp 0x00
    ACP SEID 2
> AVDTP(s): All Capabilities rsp: transaction 13 nsp 0x00
    Media Transport
    Media Codec - MPEG-2,4 AAC
      MPEG-2 AAC LC MPEG-4 AAC LC 
      44.1kHz 48kHz 
      1 2 Channels
      320000bps VBR
    Content Protection
      02 00 
    Delay Reporting
< AVDTP(s): Set config cmd: transaction 14 nsp 0x00
    ACP SEID 1 - INT SEID 1
    Media Transport
    Media Codec - SBC
      44.1kHz 
      JointStereo 
      16 Blocks
      8 Subbands
      Loudness 
      Bitpool Range 2-53
> AVDTP(s): Set config rsp: transaction 14 nsp 0x00
< AVDTP(s): Open cmd: transaction 15 nsp 0x00
    ACP SEID 1
> AVDTP(s): Open rsp: transaction 15 nsp 0x00

glibc broken on openSUSE Tumbleweed aarch64 201803

The glibc on Tumbleweed was broken since the March 2018 release.  Any call to resolve IPv4 will cause core dump.  Seems to be hitting an ARM erratum.  Details discussion can be found here.

The glibc RPMs released on 2018-04-10 seems resolved the issue.  Since DNS won't work on the affected machine, will need to manually specify IP addresses in the hosts file or copy the files to the machine and run zypper to install updates.

Here are the steps for the second approach:

- Download the RPMs from repository to another machine

glibc-2.27-4.2.aarch64.rpm

glibc-devel-2.27-4.2.aarch64.rpm

glibc-extra-2.27-4.2.aarch64.rpm

glibc-locale-2.27-4.2.aarch64.rpm

- Copy the files to the affected machine via scp.  Then remote to the affected machine and execute the followings.

- Temporarily disable remote repositories to avoid auto refresh that will cause core dump when running zypper install.

sudo zypper lr  # list repositories

sudo zypper mr -d 1  # disable the first repository

sudo zypper mr -d 2  # disable the rest

......

- Install the RPMs

sudo zypper in glibc-2.27-4.2.aarch64.rpm glibc-devel-2.27-4.2.aarch64.rpm glibc-extra-2.27-4.2.aarch64.rpm glibc-locale-2.27-4.2.aarch64.rpm

- Re-enable remote repositories

sudo zypper mr -e 1  # disable the first repository

sudo zypper mr -e 2  # disable the rest

......

- Reboot and check.  Run "sudo zypper dup" to update other packages

Generate noise

Found this interesting post on generating noise using Linux command line.  Great way to burn-in headphone?

play -n synth brownnoise synth pinknoise mix synth sine amod 0.3 10

Running Monero miner with Mesa clover

Try to run Monero miner with OpenCL on my old Linux rig.  The xmr-stak supports the official AMD APP SDK.  But since I only have access to the relatively old hardware (AMD Kabini) running Mesa clover, a quick patch is needed to make it works.

Code changes available on github.  Basically the changes are:

(1) add detection for Mesa platform vendor
(2) modify the OpenCL kernel.  Mesa clover supports OpenCL 1.1 only.  Also, although cl_amd_media_ops and cl_amd_media_ops2 are defined, some functions are missing and need definitions.

Just for reference, on my AMD Kabini 5350, the hash rate on GPU is around 18H/s when running GPU only.  Once added CPU mining, the GPU hash rate drops to about 12H/s.  And the CPU hash rate is round 28H/s.

This rig definitely not suitable if mining for profit.  But OK to support the Monero network.

Config for GPU:

gpu_threads_conf" : [
  // gpu: AMD KABINI (DRM 2.50.0 / 4.14.15-2-default, LLVM 5.0.1) memory:1302
  // compute units: 2
  { "index" : 0,
    "intensity" : 128, "worksize" : 8,
    "affine_to_cpu" : true, "strided_index" : true
  },

],

Also note that the radeon module may complain about lockup when executing long running OpenCL kernels. Add "radeon.lockup_timeout=0" Linux kernel parameter to disable the watchdog.

User LEDs on Beaglebone Black running FreeBSD

According to the DTS, the GPIO pins for the four user LEDS are pin 21-24 under gpioc1.

So, to turn them on:

sudo gpioctl -f /dev/gpioc1 21 1
sudo gpioctl -f /dev/gpioc1 22 1
sudo gpioctl -f /dev/gpioc1 23 1
sudo gpioctl -f /dev/gpioc1 24 1

Or, access them via the led driver under /dev/led

% ls -lA /dev/led
total 0
crw-------  1 root  wheel  0x33 Feb  3 15:58 beaglebone:green:heartbeat
crw-------  1 root  wheel  0x34 Feb  3 15:58 beaglebone:green:mmc0
crw-------  1 root  wheel  0x35 Feb  3 23:44 beaglebone:green:usr2
crw-------  1 root  wheel  0x36 Feb  3 15:58 beaglebone:green:usr3

Running openSUSE Tumbleweed on Odroid C2

Testing out arm64 with openSUSE Tumbleweed on Odroid C2.  The installation is pretty simple.  Follow the steps to prepare the micro-sd card.  The latest image can be found here.

The device tree of openSUSE seems a bit different from other distributions.  e.g.:

- temperature: /sys/devices/platform/scpi/scpi:sensors/hwmon/hwmon0
- blue LED: /sys/devices/platform/leds/leds/c2:blue:alive

Enable FIDO U2F on Linux

By default, only root can access the FIDO U2F device on Linux.  To change this:

• Insert the U2F device.  Note the device number and execute the following command to print out the info. e.g.

sudo udevadm info -a /dev/usb/hiddev1

• Take note of the attributes. e.g. for my HyperFIDO device:

......

ATTRS{idProduct}=="0880"

ATTRS{idVendor}=="096e"

ATTRS{ltm_capable}=="no"

ATTRS{manufacturer}=="HS"

ATTRS{maxchild}=="0"

ATTRS{product}=="HyperFIDO Token"

......

• Create a new rule file under /etc/udev/rules.d and grant permission to all users. e.g. create a file named "10-fido-key.rules" and add the followings:

SUBSYSTEMS=="usb", ATTRS{idVendor}=="096e", ATTRS{idProduct}=="0880", TAG+="uaccess"

• Re-insert the U2F device.