• the RTOS i use at work's malloc() is configured to call sbrk() to allocate memory from the system heap. free() is a no-op. this is running on a more powerful chip than an arduino. check that your system does the right thing before using dynamic memory.
  
• check the implementation of USART_Send_int for spinloops on a transmit complete status register or something else that shouldn't be in an ISR. a single character is probably going to be loaded into the transmit register and return immediately, but you might run into issues if you assume I/O works great in the interrupt context and you move on to sending long strings.
  
• i'd put a critical section in Pop() and rearrange the operations to spend less time in it:
  

  code:

  CommandNode *temp;
  critsec_enter();	//or whatever your system uses
  temp = root;
  root = root->next;
  critsec_exit();
  //now you've got a pointer to the old root via temp and Push can't be
  //creating a new node that points to the root you're about to delete
  

  i'd look at doing something similar in Push as well, but I'd change it to a queue instead of a stack were i digging around in there. you might omit it as long as you are sure that Push would always be called from an ISR, but i wouldn't risk it, especially if you're writing general library code that might be used again elsewhere. think about what might happen if your interrupt fires and calls Push() during every line of your Pop() executing in your application, then think about what CPU instructions might compose that single line of C/C++... are pointer assignments atomic, have you omitted a volatile and the value won't be guaranteed to update the actual shared memory like a static variable outside your function until the end of a call, etc.? that can be exhausting and error-prone to worry about all the time, so in general just wrap modification of shared state in a critical section. if they get too long to execute quickly, you're going to have to find a different method of doing what you want to do.

yippee cahier fucked around with this message at 18:39 on Aug 9, 2015

Luigi Thirty fucked around with this message at 04:51 on Aug 12, 2015