topic Re: USART interrupt on LPC55S69 Board not receiving more than 17 bytes in LPC Microcontrollers

USART interrupt on LPC55S69 Board not receiving more than 17 bytes

sushmasan — Wed, 07 May 2025 16:30:59 GMT

Hello Team,

I tried different possibilities, but in the USART interrupt handler I am able to receive only receive only 17bytes.

This is my interrupt handler code, please let me know if I am missing anything,

#define BUFF_SIZE 256 uint8_t rx_buffer[BUFF_SIZE]; void Test_USART2_IRQHandler(void) { uint8_t data; while ((0x1F<<USART_FIFOSTAT_RXLVL_SHIFT) & (USART_IF2->FIFOSTAT)) { data = USART_ReadByte(USART_IF2); if (((rxHeadIndex + 1) % BUFFER_SIZE) != rxTailIndex) { rxBuffer[rxHeadIndex] = data; rxHeadIndex++; rxHeadIndex %= BUFFER_SIZE; } } USART_DisableInterrupts( USART_IF2, kUSART_RxLevelInterruptEnable | kUSART_RxErrorInterruptEnable ); SDK_ISR_EXIT_BARRIER; } // Processing the received data in another task, and enabling interrupts after copying the complete data.

With this I am receiving this data,

Received -> 1 Received -> 2 Received -> 3 Received -> 4 Received -> 5 Received -> 6 Received -> 7 Received -> 8 Received -> 9 Received -> 10 Received -> 11 Received -> 12 Received -> 13 Received -> 14 Received -> 15 Received -> 16 Received -> 17

In the same interrupt handler code, If I include these lines, after USART_ReadByte,

// Check for the RX FIFO Overflow error and if exist, clear that error if ((USART_IF2->FIFOSTAT & USART_FIFOSTAT_RXERR_MASK)) { PRINTF("RX FIFO Overflow error, so clearing it\r\n"); USART_IF2->FIFOSTAT |= USART_FIFOSTAT_RXERR_MASK; }

I am receiving this data,

Received -> 1 RX FIFO Overflow error, so clearing it Received -> 2 Received -> 3 Received -> 4 Received -> 5 Received -> 6 Received -> 7 Received -> 8 Received -> 9 Received -> 10 Received -> 11 Received -> 12 Received -> 13 Received -> 14 Received -> 15 Received -> 16 Received -> 17

But the other device is sending 30bytes to LPC55S69.

Can you please let me know, where the other bytes lost and why those are not received fully?

Regards,

San

Re: USART interrupt on LPC55S69 Board not receiving more than 17 bytes

EdwinHz — Wed, 07 May 2025 18:10:25 GMT

Hi @sushmasan,

Please take a look at our USART example codes from the LPCXpresso55s69 SDK as these example codes will prove useful for your issue. You can download the SDK on the following link: Select Board | MCUXpresso SDK Builder

BR,
Edwin.

Re: USART interrupt on LPC55S69 Board not receiving more than 17 bytes

sushmasan — Wed, 07 May 2025 18:58:26 GMT

Hi @EdwinHz ,

Thanks for your response.

I already tried example code between two USART and even tested loop back mode.

But in my application the data is sent by another device to LPC55S69.

I also saw an explanation in this thread, but still I am seeing the issue.

https://community.nxp.com/t5/LPC-Microcontrollers/USART-interrupt-on-LPC55S69-Board/td-p/1848624

Regards,
San

Re: USART interrupt on LPC55S69 Board not receiving more than 17 bytes

EdwinHz — Wed, 14 May 2025 19:09:23 GMT

Hi @sushmasan,

As you can see in section "34.6.10 FIFO Configuration register" of the "LPC55S6x/LPC55S2x/LPC552x User manual" (UM11126), the USART FIFO size is forcefully configured as 16 entries of 8 bits.

This is why you are only receiving 16 entries (1 through 17).

As mentioned on the following community post, you need to clear the FIFO in order to receive more than 16 bytes: Re: Receiving Moren Than 16 Data via USART - NXP Community.

BR,
Edwin.

Re: USART interrupt on LPC55S69 Board not receiving more than 17 bytes

sushmasan — Thu, 15 May 2025 13:55:27 GMT

Hi @EdwinHz ,

Thanks for your response.

I am not doing it correctly to clear the RX fifo overflow. Also I found another cause, as I am using a debug message inside the interrupt handler that is causing the issue.

Now everything is working fine.

Regards,
San