Exception in rosserial 'hello world' example

asked 2013-01-18 08:34:09 -0500

danep
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I am trying to implement rosserial on a new platform (STM32F0-Discovery board, which has a Cortex-M0 processor and is quite a bit more powerful than the Arduino, so I think it should be possible).

I've created a simple 'hello world' program, based on the hello world example for rosserial_arduino, which simply publishes the std_msgs::String 'hello world'.

I can upload and run the example on the board, and it receives data over the serial port. Unfortunately, once I run serial_node.py on my host, the board throws an exception (hard fault) in TopicInfo.h at line 42:

memcpy(outbuffer + offset, this->message_type, *length_message_type);

The values of the variables there look a little odd to me, but I'm not exactly sure what they should look like. offset seems correct (13, which matches 'std_msgs::String'). message_type seems corrupted though- it's a jumble of characters with elements of 'std_msgs' and 'String' embedded in it. I'm not sure if that indicates actual corruption, or if the debugger just isn't interpreting it correctly.

I'm really at a loss- any advice would be appreciated!

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Hey danep, I'm also trying to do the same on STM32F103. Could you tell me as to how you implemented the rosserial on the the stm32?

kartikmadhira1 ( 2016-12-26 19:44:46 -0500 )edit

I believe I used protocol buffers to handle the memory alignment issues. Unfortunately I haven't used this library in years so I can't be more specific. See my answer here: http://answers.ros.org/question/58388...

danep ( 2016-12-26 21:23:52 -0500 )edit

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answered 2013-01-23 07:00:26 -0500

danep
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updated 2013-01-25 06:07:50 -0500

Okay, so a few things... first of all, I think the garbled variables were due to compile-time optimization. Once I disabled C/C++ optimization, the variables looked much more reasonable.

Disabling optimization also allowed me to realize that the problem has nothing to do with memcpy- it's due to the following lines:

 uint32_t * length_message_type = (uint32_t *)(outbuffer + offset);
*length_message_type = strlen( (const char*) this->message_type);

The real cause of this error, I think, is a problem with memory addressing. If I add '1' to outbuffer + offset above, the assignment works fine (although the program fails later on). So it would seem that length_message_type is partially overwriting the variable defined just before it. I'll probably open a trac bug for this, but I welcome any suggestions on how to fix this myself.

EDIT: The problem was indeed with memory alignment. Rosserial was written for the Arduino, an 8-bit platform, but I am implementing it on an STM32F0, a 32-bit platform. On 32-bit platforms, you must take care when writing to RAM that the address is divisible by 4 for proper alignment.

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How would I apply this fix to using rosserial with a chipkit max32?

packrat ( 2013-03-26 10:49:48 -0500 )edit

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Exception in rosserial 'hello world' example

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