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Strange Time Sequence of UART Rx Interrupt and its Flag for KEA128

Question asked by fortunely X on Jan 5, 2020
Latest reply on Jan 7, 2020 by Alexis Andalon

Hi NXP team,

I am developing a UART bootloader using FRDM-KEAZ128Q80. I want to realize a UART2 fifo by software, so i have to use UART2 receiving way by interrupting. But strange time sequence of UART rx interrupt and its flag occurs to me, that is,

1) only one interrupt Rx interrupt(UART2_C2[RIE]: Receiver Interrupt Enable for RDRF) is enabled;

2) program can run to UART2_IRQHandler(UART2 interrupt handle function in uart.c), when I transmit one byte data to board by Tera Term VT(virtual COM tools);


3) UART2_S1[RDRF] would be 0, when program enters into UART2_IRQHandler() and use UART_IsRxBuffFull() to query Rx buffer of UART; but if i use UART_GetChar(), the program can get the status of UART2_S1[RDRF] .



Expectation :

when evb receives a uart byte data, then run to uart interrupt handle and get the interrupt flag RDRF==1, but actually it is RDRF==1 if i query the flag at once in interrupt handle.

When i can get the flag set(RDRF == 1)? it seems i have to use a polling loop to wait the flag.


I dont know why ? if i use a while loop in my interrupt handle, i am warried that the loop wasting much time for wating  RDRF  set and even program will go stuck in the loop especially program cant get the flag set.


Environment and tools


IDE: S32DS for ARM 2018.R1;


SDK: 1.0.0

uart driver: uart.c, .h

UART configuration: BUS 20MHz, UART2 baud rate=115200bps, enable receive buffer full interrupt and receive function


My uart configuration:




void UartManager_Init()
UART_ConfigType sUartConfig = {{0}};
sUartConfig.u32SysClkHz = BUS_CLK_FREQ; // 20MHz(20000000)
sUartConfig.u32Baudrate = UART_BIT_BAUDRATE; // 115200kbps

sUartConfig.sctrl1settings.byte = 0;

sUartConfig.sctrl2settings.bits.bTe = 1; // transmitter enable
sUartConfig.sctrl2settings.bits.bRe = 1; // receive enable
sUartConfig.sctrl2settings.bits.bRie = 1; // receive buffer full interrupt enable

UART_SetCallback(TERMINAL_UART_PORT, UartManager_Interrupt);



void UartManager_Interrupt(void)
volatile uint8_t data = 0;


/*only use 1 case (case 1, 2, 3) for test*/


// case 1 - success to read flag RDRF and uart data

// data = UART_GetChar(TERMINAL_UART_PORT); // can get the received char


// case 2 - success to read flag RDRF and uart data

//while(!UART_IsRxBuffFull(TERMINAL_UART_PORT)); // can pass the loop, which means RDRF==1

//data = UART_ReadDataReg(TERMINAL_UART_PORT);


// case 3 - failure to read flag RDRF and uart data

/* if(UART_IsRxBuffFull(TERMINAL_UART_PORT)){ // cant get the flag RDRF == 1, it will run to else condition