Multitask error @uart example

lpcware — Thu, 16 Jun 2016 02:55:03 GMT

Content originally posted in LPCWare by wortel on Mon Feb 14 05:02:38 MST 2011
In the UART example it is possible to end in a endless loop when using priority interrupts and/or FreeRtOS.

This is the part:

      /* THRE status, contain valid data */
      while ( !(UART1TxEmpty & 0x01) );    
      LPC_UART1->THR = *BufferPtr;
      UART1TxEmpty = 0;    /* not empty in the THR until it shifts out */

it should be like this:

      /* THRE status, contain valid data */
      while ( !(UART3TxEmpty & 0x01) );
      UART3TxEmpty = 0;    /* not empty in the THR until it shifts out */
      LPC_UART3->THR = *BufferPtr;

Else it is possible to have the character send already, where the interrupt services that the Empty bit gets Empty = 1;, and where later on the running code then clears the bit. Resulting in a endless loop the next time that you will send a char, since the interrupt was already done.

Is it OK that I post this error? Or isn't it appropriated.

Re: Multitask error @uart example

lpcware — Thu, 16 Jun 2016 02:55:04 GMT

Content originally posted in LPCWare by NXP_USA on Tue Feb 15 11:13:46 MST 2011
The UART driver code is not re-entrant. In a multitasking environment it should be placed into a single resource-management thread or the global variables should be replaced with semaphores. I am not certain moving the "UART3TxEmpty" assignment will completely work around this.

-NXP

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