Category: Dicas

Checking the CRC-8 PEC byte of MLX90614

I am creating a NuttX device driver for Melexis MLX90614 and it is a nice adventure.

First I downloaded the adafruit lib and tested it on Arduino Uno just to confirm the sensor was working, but I didn’t look the source code because I always prefer to read the datasheet and implement the driver from scratch.

All things fine, the mlxtest example worked correctly and I got the ambient temperature and the object temperature printed correctly.

Then I created the driver and decided to test it on STM32F103, but discovered that I2C_TRANSFER() for STM32F103 is broken. No problem, let to test it on STM32F4Discovery board:

nsh> dd if=/dev/thermo0 of=/dev/null bs=2 count=1
mlx90614_read_word: value[0]: 0xDF | value[1]: 0x3A | value[2]: 0xCF | ret: 0

Let see in the logic analyzer to confirm:

Very good! But how to check if CRC-8 PEC field (third received byte: 0xCF) is correct?

I found this nice online CRC calculator:

http://www.sunshine2k.de/coding/javascript/crc/crc_js.html

But putting all values as suggested in the datasheet didn’t work:

0x5A 0x06 0x5A 0xDF 0x3A
Result CRC value: 0x2F

Then just web searching for: MLX90614 PEC CRC-8 example

Returned me this thread:

https://stackoverflow.com/questions/20554869/implementing-crc8-on-arduino-to-write-to-mlx90614

The “thb” guy saved me:

“I haven’t checked your CRC implementation but there is a mistake in the MLX datasheet or at least it’s badly written. You have to include all the I2C frame’s data for the PEC’s calculation not just the replied data. For a read word command you have to include [SA_W, Command, SA_R, LSB, MSB] and for a write word command [SA_W, Command, LSB, MSB]. So, for their first example the calculation must be made on [ 0xB4, 0x07, 0xB5, 0xD2, 0x3A ] and not just on [ 0xD2, 0x3A ] and this way you get the expected 0x30.”

What this guy is saying is: we need to include all the bits of the Slave Address, the address needs to be seen as 8-bit including the the less significant bit Write or Read. So I2C Write at address 0x5A is seen as 0xB4 and I2C Read is seen as 0xB5 (pay attention at bits over the “5A” in the logic analyzer image above).

So, let to try his idea:

0xB4 0x06 0xB5 0xDF 0x3A
Result CRC value: 0xCF

Bingo!

the moon… beautiful! oh yeah!

Today I decided to test the Lua (the programming language, it means Moon in Portuguese) with FLTK. There is a project called lua-fltk4lua.

Unfortunately the project doesn’t explain how to compile it from source code and it expects the developer uses the “luarocks” package manager to install it.

Although initially I was getting some issues like:

No rule to make target “moon/moon.h”
No rule to make target “compat-5.3/c-api/compat-5.3.h”

I figured out how to get it compiled and working easily, find the steps below:

$ sudo apt-get install lua5.2

$ sudo apt-get install liblua5.2-dev

$ sudo apt-get install libfltk1.3-dev

$ git clone https://github.com/siffiejoe/lua-fltk4lua

$ cd lua-fltk4lua

$ git clone https://github.com/siffiejoe/lua-moon moon

$ git clone https://github.com/keplerproject/lua-compat-5.3 compat-5.3

$ make

$ sudo make install

This is a nice Hello World to see it working, just create a hello.lua file with it:

local fl = require( "fltk4lua" )
local window = fl.Window( 340, 180, "Hello" )
local box = fl.Box( 20, 40, 300, 100, "Hello World!" )
box.box = "FL_UP_BOX"
box.labelfont = "FL_HELVETICA_BOLD_ITALIC"
box.labelsize = 36
box.labeltype = "FL_SHADOW_LABEL"
window:end_group()
window:show( arg )
fl.run()

And run:

$ lua hello.lua

Just it!

Using FAT32 long file names on NuttX

NuttX supports FAT32 with long file names, but there is some details that you need to know to get it working. I will share here the issues that I was facing and how I fixed it.

The original FAT uses 8.3 (8 chars for name and 3 chars for extension), but it can supports files with up to 255 characters (including the extension).

To use it we need to enable long file name support in the menuconfig:

 File Systems  --->
     [*] FAT file system
     [*]   FAT upper/lower names
     [*]   FAT long file names             -------->  (CONFIG_FAT_LFN=y)
     (255)   FAT maximum file name size    -------->  (CONFIG_FAT_MAXFNAME=255)

Initially I will mount an empty SDCard to do my tests:

NuttShell (NSH)

nsh> mount -t vfat /dev/mmcsd0 /mnt

nsh> ls /mnt
/mnt:

nsh>

Let’s to create a small 8.3 file that will be renamed:

nsh> echo "Small file" > /mnt/tinyfile.txt
nsh> ls -l /mnt/tinyfile.txt
 -rw-rw-rw-      12 /mnt/tinyfile.txt
nsh>

Now I will try to rename it to a file with a long name:

nsh> mv /mnt/tinyfile.txt /mnt/this_is_a_file_with_a_long_name_jnsh>

Strange, while I was typing “this_is_a_file_with_a_long_name_just_for_test.txt” the typing was interrupted and the nsh> appeared.

Let see if the file was renamed:

nsh> ls /mnt
/mnt:
 this_is_a_file_with_a_long_name_

Then I remembered that the max line size of NSH was just 60 (CONFIG_NSH_LINELEN=60), I will increase it to 300 characters:

Application Configuration  --->
    NSH Library  --->
          Command Line Configuration  --->
              (300) Max command line length    -------->  (CONFIG_NSH_LINELEN=300)

I will create a tinyfile.txt again and try to rename it:

nsh> mv /mnt/tinyfile.txt /mnt/this_is_a_file_with_a_long_name_just_for_test.txt
nsh> 

Right, now the nsh prompt accept the enter the name, but let see if the file was created correctly:

nsh> ls /mnt
/mnt:
 this_is_a_file_with_a_long_name_
 this_is_a_file_with_a_long_name_

Whoa, it created two files with same name? How it is possible? Don’t worry, these files are different. Opening the SDCard in the Linux I can see:

this_is_a_file_with_a_long_name_j
this_is_a_file_with_a_long_name_just_for_test.txt

So, the LS command is showing only 32 characters. After some investigation I discovered that CONFIG_NAME_MAX=32 was the issue. Let to increase it to 255:

RTOS Features  --->
    Files and I/O  --->
        (255) Maximum size of a file name    -------->  (CONFIG_NAME_MAX=255)

Now I can see the files:

nsh> ls /mnt
/mnt:
 this_is_a_file_with_a_long_name_j
 this_is_a_file_with_a_long_name_just_for_test.txt

My next step is to create a file with 255 characters, like this:

this_file_will_have_a_big_filename_to_verify_how_to_work_with_files_with_long_names_our_test_need_to_have_the_max_filename_size_supported_by_fat32_that_means_it_could_have_up_to_255_characters_including_the_extension_in_the_filename_so_here_we_arrived.txt

nsh> echo "Test" > /mnt/this_file_will_have_a_big_filename_to_verify_how_to_work_with_files_with_long_names_our_test_need_to_have_the_max_filename_size_supported_by_fat32_that_means_it_could_have_up_to_255_characters_including_the_extension_in_the_filename_so_here_we_arrived.txt
nsh> ls /mnt
/mnt:
 this_file_will_have_a_big_filename_to_verify_how_to_work_with_files_with_long_names_our_test_need_to_have_the_max_filename_size_supported_by_fat32_that_means_it_could_have_up_to_255_characters_including_the_extension_in_the_filename_so_here_we_arrived.txt
nsh> 

Very nice! It worked correctly.

As you can see NuttX is similar to Linux kernel, many features depends on other features’ configuration. They are inter-dependent.

Fashing a bad firmware can drive your crazy

I put by XMC4500 in a state where OpenOCD was unable the communicate with it:

$ sudo openocd -f board/xmc4500-relax.cfg -c init -c "reset halt" -c "flash write_image erase nuttx.bin 0x0c000000"
Open On-Chip Debugger 0.10.0+dev-00172-g7719e96 (2017-11-12-09:13)
Licensed under GNU GPL v2
For bug reports, read
	http://openocd.org/doc/doxygen/bugs.html
adapter speed: 4000 kHz
cortex_m reset_config sysresetreq
adapter speed: 1000 kHz
Info : No device selected, using first device.
Info : J-Link Lite-XMC4000 Rev.1 compiled Apr  2 2015 18:25:20
Info : Hardware version: 1.00
Info : VTarget = 3.300 V
Info : clock speed 1000 kHz
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Error: Could not initialize the debug port
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Info : SWD DPIDR 0x2ba01477
Error: Could not initialize the debug port
Error: Target not examined, reset NOT asserted!
in procedure 'reset' 
in procedure 'ocd_bouncer'

What happened?

I just changed BOARD_SYSDIV :

#  define BOARD_SYSDIV              0

But in clockconfig.c it does:

  /* Setup fSYS clock */

  regval  = (BOARD_ENABLE_PLL << SCU_SYSCLKCR_SYSSEL);
  regval |= SCU_SYSCLKCR_SYSDIV(BOARD_SYSDIV);
  putreg32(regval, XMC4_SCU_SYSCLKCR);

SCU_SYSCLKCR_SYSDIV is defined this way:

#  define SCU_SYSCLKCR_SYSDIV(n)    ((uint32_t)((n)-1) << SCU_SYSCLKCR_SYSDIV_SHIFT)

So, it wrote 0xffffffff to SCU_SYSCLKCR register. :-/

Then I tried to flash using JLinkExe from Segger, but it also didn’t work:

$ JLinkExe -if SWD
SEGGER J-Link Commander V6.14h (Compiled May 10 2017 18:39:45)
DLL version V6.14h, compiled May 10 2017 18:39:37

Connecting to J-Link via USB...O.K.
Firmware: J-Link Lite-XMC4000 Rev.1 compiled Apr  2 2015 18:25:20
Hardware version: V1.00
S/N: 551014400
VTref = 3.300V


Type "connect" to establish a target connection, '?' for help
J-Link>connect
Please specify device / core. : XMC4500-1024
Type '?' for selection dialog
Device>
Specify target interface speed [kHz]. : 4000 kHz
Speed>
Device "XMC4500-1024" selected.


Performing XMC4500 connection sequence.
No AP preselected. Assuming that AP[0] is the AHB-AP
AP-IDR: 0x24770011, Type: AHB-AP
AHB-AP ROM: 0xE00FF000 (Base addr. of first ROM table)
Found Cortex-M4 r0p1, Little endian.
FPUnit: 6 code (BP) slots and 2 literal slots
CoreSight components:
ROMTbl[0] @ E00FF000
ROMTbl[0][0]: E000E000, CID: B105E00D, PID: 000BB00C SCS
ROMTbl[0][1]: E0001000, CID: B105E00D, PID: 003BB002 DWT
ROMTbl[0][2]: E0002000, CID: B105E00D, PID: 002BB003 FPB
ROMTbl[0][3]: E0000000, CID: B105E00D, PID: 003BB001 ITM
ROMTbl[0][4]: E0040000, CID: B105900D, PID: 000BB9A1 TPIU
ROMTbl[0][5]: E0041000, CID: B105900D, PID: 000BB925 ETM
Cortex-M4 identified.
J-Link>loadbin ./nuttx.bin 0
Downloading file [./nuttx.bin]...
Writing target memory failed.

Fortunately the “erase” command worked:

J-Link>erase
Erasing device (XMC4500-1024)...
Comparing flash   [100%] Done.
Erasing flash     [100%] Done.
Verifying flash   [100%] Done.
J-Link: Flash download: Total time needed: 22.650s (Prepare: 0.041s, Compare: 0.000s, Erase: 22.604s, Program: 0.000s, Verify: 0.000s, Restore: 0.004s)
Erasing done.

But even after the flash erase the programming is not working:

J-Link>loadbin ./nuttx.bin 0
Downloading file [./nuttx.bin]...
Writing target memory failed.
J-Link>

Then I decided to try OpenOCD again:

$ sudo openocd -f board/xmc4500-relax.cfg
Open On-Chip Debugger 0.10.0+dev-00172-g7719e96 (2017-11-12-09:13)
Licensed under GNU GPL v2
For bug reports, read
	http://openocd.org/doc/doxygen/bugs.html
adapter speed: 4000 kHz
cortex_m reset_config sysresetreq
adapter speed: 1000 kHz
Info : No device selected, using first device.
Info : J-Link Lite-XMC4000 Rev.1 compiled Apr  2 2015 18:25:20
Info : Hardware version: 1.00
Info : VTarget = 3.300 V
Info : clock speed 1000 kHz
Info : SWD DPIDR 0x2ba01477
Info : xmc4500.cpu: hardware has 6 breakpoints, 4 watchpoints
Info : accepting 'telnet' connection on tcp/4444

And using telnet I tried to send the reset command:

$ telnet 127.0.0.1 4444
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
Open On-Chip Debugger
> reset halt
timed out while waiting for target halted
TARGET: xmc4500.cpu - Not halted
in procedure 'reset' 
in procedure 'ocd_bouncer'


Halt timed out, wake up GDB.
> 

At this moment I thought my board could be damaged, but I decided to try to flash it anyway:

> flash write_image erase nuttx.bin 0x0c000000
auto erase enabled
Cannot communicate... target not halted.
auto_probe failed

Hmm, let to test only “halt” instead of “reset halt” :

> halt
target halted due to debug-request, current mode: Thread 
xPSR: 0x41000000 pc: 0x000000e6 msp: 0x2000ff3c

Good, now let to try again:

> flash write_image erase nuttx.bin 0x0c000000
auto erase enabled
Clearing flash status
Clearing flash status
wrote 81920 bytes from file nuttx.bin in 17.523651s (4.565 KiB/s)

Very good, my board is live again!

How to avoid cloning full git repository

I was used to clone the NuttX git repository all the time I need a clean copy. But this is not a good idea, because it waste time and increase the network traffic.

Sebastien Loquert gave a suggestion to improve it:

$ sudo mkdir /opt/nuttx

$ cd /opt/nuttx

$ git clone https://bitbucket.org/nuttx/nuttx

$ git clone https://bitbucket.org/nuttx/apps

$ cd ~/nuttxspace

$ git clone /opt/nuttx/nuttx nuttx

$ git clone /opt/nuttx/apps apps

$ cd nuttx

$ git pull

$ cd ../apps

$ git pull

This simple tips will reduce the time I waste download the full repository and will reduce the network traffic. It is important if you are using 3G/4G and you pay by amount of the downloaded data.

Programming the Nucleo-L476RG with OpenOCD

I decide to use the Nucleo-L476RG board (MB1136 C-04) to test NuttX. This is the same board that Mihail is using to create his nice tutorials:
http://cmn-lab.com

It comes with a detachable (“break apart”, please don’t do it) stlink-v2.1 programmer, but I didn’t get it working with OpenOCD, then I decided to use an external stlink-v2 clone to program it.

All you need to do is connect the SWDIO pin from programmer to pin PA13 (CN7 pin 13), SWCLK pin to PA14 (CN7 pin 15) and the GND pin (i.e. CN7 pin 20).

The command to flash the nuttx.bin firmware was this one:

 $ sudo openocd -f interface/stlink-v2.cfg -f target/stm32l4x.cfg -c init -c "reset halt" -c "flash write_image erase nuttx.bin 0x08000000"

Now just open the minicom configuring it to use the STLInk Debug port (ttyACM0).

Update: today testing the about OpenOCD command again using the stlink-v2.1 existent in the board it worked fine. Using “Open On-Chip Debugger 0.10.0+dev-00376-g3d3b45a (2018-04-03-20:18)”