Bug in SDK 2.5.0 for LPC804 (and maybe other micros) in fsl_usart.c

[mike_katz]

Version 2.0.0 of the fsl_usart driver from the LPC804 SDK has the following code snippet from the USART_SetBaudRate() function (this works):

            diff = baudrate_Bps < baudrate ? baudrate - baudrate_Bps : baudrate_Bps - baudrate;
            if (diff < best_diff)
            {
                best_diff = diff;
                best_osrval = osrval;
                best_brgval = brgval;
            }
        }

        /* value over range */
        if (best_brgval > 0xFFFF)
        {
            return kStatus_USART_BaudrateNotSupport;
        }

        base->OSR = best_osrval;
        base->BRG = best_brgval;
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Version 2.0.1 of the fsl_usart driver has the following code:

            diff = baudrate_Bps < baudrate ? baudrate - baudrate_Bps : baudrate_Bps - baudrate;
            if (diff < best_diff)
            {
                best_diff = diff;
                best_osrval = osrval;
                best_brgval = brgval;
            }
        }

        /* value over range */
        if (best_brgval > 0xFFFF)
        {
            return kStatus_USART_BaudrateNotSupport;
        }

        /* If the baud rate caculated is not very precise, please select the FRG clock as
         * the USART's source clock, and set the FRG frequency to a more suitable value.
         */
        assert(diff < ((baudrate_Bps / 100) * 3));

        base->OSR = best_osrval;
        base->BRG = best_brgval;

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The assert on line 17 is new and is incorrect.

The assert should be:   

assert( best_diff < ((baudrate_Bps / 100) * 3));

The purpose of the assert is to insure that a valid baud rate multiplier has been found.  The value that is used to determine this is stored in best_diff, diff is used as temporary calculation holder.

[jeremyzhou]

Hi Mike Katz,

Thank you for your interest in NXP Semiconductor products and
for the opportunity to serve you.
Yes, it should be replaced by the below code, I'll report it to SDK team for checking.

assert( best_diff < ((baudrate_Bps / 100) * 3));‍‍‍

Have a great day,
TIC

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