PIC32MX270F256B UART : how to get a single byte from the RX FIFO? - pic

Question

I'm trying to read byte per byte from the RX FIFO, that's 8 bytes deep.
The problem is that when the first byte is received, I have to wait for 8 other bytes to finally get the first byte on U1RXREG.
I'd like to know how to perform some dummy reads on the FIFO to access a particuar byte and "flush" it. Simply putting U1RXREG in an array doesn't do the trick.
Here's my initialization :
void UART_Initialize(void)
{
// SIDL: Stop in Idle Mode bit : 1 = Discontinue module operation when the device enters Idle mode
U1MODEbits.SIDL = 0;
// IREN: IrDA Encoder and Decoder Enable bit : 0 = IrDA is disabled
U1MODEbits.IREN = 0;
// RTSMD: Mode Selection for UxRTS Pin bit : 0 = UxRTS pin is in Flow Control mode
U1MODEbits.RTSMD = 0;
// UEN<1:0>: UARTx Enable bits : 10 = UxTX, UxRX, UxCTS and UxRTS pins are enabled and used
U1MODEbits.UEN1 = 1;
U1MODEbits.UEN0 = 0;
// WAKE: Enable Wake-up on Start bit Detect During Sleep Mode bit : 0 = Wake-up disabled
U1MODEbits.WAKE = 0;
// LPBACK: UARTx Loopback Mode Select bit : 0 = Loopback mode is disabled
U1MODEbits.LPBACK = 0;
// ABAUD: Auto-Baud Enable bit : 0 = Baud rate measurement disabled or completed
U1MODEbits.ABAUD = 0;
// RXINV: Receive Polarity Inversion bit : 0 = UxRX Idle state is ‘1’
U1MODEbits.RXINV = 0;
// BRGH: High Baud Rate Enable bit : 0 = Standard Speed mode – 16x baud clock enabled
U1MODEbits.BRGH = 0;
// PDSEL<1:0>: Parity and Data Selection bits : 01 = 8-bit data, even parity
U1MODEbits.PDSEL1 = 0;
U1MODEbits.PDSEL0 = 1;
// STSEL: Stop Selection bit : 0 = 1 Stop bit
U1MODEbits.STSEL = 0;
// ADM_EN: Automatic Address Detect Mode Enable bit : 0 = Automatic Address Detect mode is disabled
U1STAbits.ADM_EN = 0;
// UTXISEL<1:0>: TX Interrupt Mode Selection bits : 00 = Interrupt is generated and asserted while the transmit buffer contains at least one empty space
U1STAbits.UTXISEL1 = 0;
U1STAbits.UTXISEL0 = 0;
// UTXINV: Transmit Polarity Inversion bit : 0 = UxTX Idle state is ‘1’ (with IrDA disbled)
U1STAbits.UTXINV = 0;
// URXEN: Receiver Enable bit : 1 = UARTx receiver is enabled. UxRX pin is controlled by UARTx (if ON = 1)
U1STAbits.URXEN = 1;
// UTXBRK: Transmit Break bit : 0 = Break transmission is disabled or completed
U1STAbits.UTXBRK = 0;
// URXISEL<1:0>: Receive Interrupt Mode Selection bit : 00 = Interrupt flag bit is asserted while receive buffer is not empty (i.e., has at least 1 data character)
U1STAbits.URXISEL1 = 0;
U1STAbits.URXISEL0 = 0;
// ADDEN: Address Character Detect bit (bit 8 of received data = 1) : 0 = Address Detect mode is disabled
U1STAbits.ADDEN = 0;
// Baud Rate Calculation :
// FPB = 10MHz ; Desired Baud Rate = 9600 bauds
// => U1BRG = FPB/(16*BaudRate)-1 = 64 (error = 0,16%)
U1BRG = 64;
// Enable UART RX interrupts
//IEC1bits.U1RXIE = 1;
// Enable UART
// ON: UARTx Enable bit : 1 = UARTx is enabled. UARTx pins are controlled by UARTx as defined by the UEN<1:0> and UTXEN control bits.
U1MODEbits.ON = 1;
// UTXEN: Transmit Enable bit : 1 = UARTx transmitter is enabled. UxTX pin is controlled by UARTx (if ON = 1).
U1STAbits.UTXEN = 1;
}
For the moment I tried reading like this, in the while(1) loop, without success :
while (1)
{
uint8_t rxbyte[8];
bool b;
//if (U1STAbits.URXDA == 1)
while(!U1STAbits.URXDA);
rxbyte[0] = U1RXREG;
rxbyte[1] = U1RXREG;
rxbyte[2] = U1RXREG;
rxbyte[3] = U1RXREG;
rxbyte[4] = U1RXREG;
rxbyte[5] = U1RXREG;
rxbyte[6] = U1RXREG;
rxbyte[7] = U1RXREG;
sprintf(s, "I received : %u %u %u %u %u %u %u %u\n\r", rxbyte[0], rxbyte[1], rxbyte[2], rxbyte[3], rxbyte[4], rxbyte[5], rxbyte[6], rxbyte[7]);
myPrint(s);
IFS1bits.U1RXIF = 0;
}
The 8 bytes in rxbytes[] are always the same. I tried to clear the RX interrupt flag between the reads, reading URXDA also between the reads, add a delay, still no success, I still have to wait for 8 incoming bytes to access the first one.
Thanx in advance for your help !
Best regards.
Eric

Answer 1

I finally found the solution : I had a double configuration, one by MCC and one by myself, and it seems that having the interruptions activated caused this. Now I switched the interrupts off and I simply poll URXDA, and everything works fine.
Sorry for bothering you guys !

Answer 2

You can use your original method too. The problem with your While(1) loop is that you check if there is "at least 1 byte in the hardware Rx buffer" ( U1STAbits.URXDA tells you as soon as 1 byte is availlable ). When 1 byte is availlable, then you read 8 bytes inside the loop... so of course you will get 8 identical bytes when there is only 1 byte in the buffer.