Kevin Braun

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9 years, 12 months ago.

Fixing missing Rx serial chars on the K64F

Hello,

Here is a quick fix when using the USB serial port at higher speeds (e.g. 230400). This current problem is that back-to-back characters get missed when multiple characters are sent to the K64F. Typical examples are Enter (CR LF) and up-arrow (ESC [ A), etc. The ISR cannot respond fast enough to receive all characters. This can be fixed by enabling the UART's Rx FIFO on the K64F. Example:

RawSerial pc(USBTX, USBRX);

int main() {
    // init code....
    pc.baud(230400);
    pc.printf("Hello World!!\r\n");

    // enable the usb uart rx fifo
    UART_PFIFO_REG(UART0) |= 0x08;

    // enable the UART Rx callback interrupt
    pc.attach(&PcRxIRQ, pc.RxIrq);

    // more code
}

The default UART Rx FIFO depth is 8 characters. This seems fine to me.

...kevin

I think it is a bit weird if it wouldn't be fast enough to handle that, even at that baudrate it is slow compared to other interfaces.

Although if there is a FIFO it should be enabled by default.

posted by Erik - 08 May 2014

Currently, it is not enabled

...kevin

posted by Kevin Braun 08 May 2014

1 Answer

Ned Konz
9 years, 12 months ago.

It might be better to use the more careful Freescale UART HAL routines:

#include "mbed.h"
#include "fsl_uart_hal.h"

static void enable_rx_fifo(int instance)
{
    uart_hal_disable_receiver(instance);
    uart_hal_disable_transmitter(instance);
    uart_hal_enable_rx_fifo(instance);
    uart_hal_enable_receiver(instance);
    uart_hal_enable_transmitter(instance);
    uart_hal_flush_rx_fifo(instance);
    uart_hal_flush_tx_fifo(instance);
}
    
int main()
{
    // USBTX/USBRX is connected to UART0
    RawSerial pc(USBTX, USBRX);
    enable_rx_fifo(0);
    // rest of program...
}

Also, in your interrupt handler you may have to handle more than one character from the FIFO.

Accepted Answer

Thanks Ned,

My interrupt handler does accept multiple characters.

...kevin

posted by Kevin Braun 08 May 2014