UART Sending Extra 0x00 Bytes

[neuro]

Hello,

I am working on a IMX6 Solo X chip with Linux and using 3 UARTS (RS485) to send/receive data from the serial ports interfacing with another board. I'm simply testing these ports with a simple C program utilizing Linux libraries (termios, read, write) by sending and receiving simple messages (e.g. ABCDEFGHIJ).

I'm reading bytes from the external board fine, however, anytime i send bytes, the external board receives a large amount of 0x00 bytes that come after the bytes i sent.

What can I do to prevent these extra 0x00 bytes from being sent after my initial message? I preferably do not want to modify the external boards code to band aid this.

I have been reading some other posts and it seems like it might be the DMA, however, I also was reading the uarts have to have DMA enabled. Is this true or can i disable DMA?

An example device tree node for a uart is setup as such:

uart3: serial@021ec000 {
                compatible = "fsl,imx6sx-uart",
                         "fsl,imx6q-uart", "fsl,imx21-uart";
                reg = <0x021ec000 0x4000>;
                interrupts = <GIC_SPI 28 IRQ_TYPE_LEVEL_HIGH>;
                clocks = <&clks IMX6SX_CLK_UART_IPG>,
                     <&clks IMX6SX_CLK_UART_SERIAL>;
                clock-names = "ipg", "per";
                dmas = <&sdma 29 4 0>, <&sdma 30 4 0>;
                dma-names = "rx", "tx";
                status = "disabled";
};

pinctrl_uart3: uart3grp {
            fsl,pins = <
                MX6SX_PAD_NAND_DATA04__GPIO4_IO_8    0x1b0b1
                MX6SX_PAD_NAND_DATA06__UART3_RX        0x1b0b1
                MX6SX_PAD_NAND_DATA07__UART3_TX        0x1b0b1
            >;
 };

&uart3 {
    pinctrl-names = "default";
    pinctrl-0 = <&pinctrl_uart3>;
    dma-names = "","tx";
    status = "okay";
};

Thank you

[neuro]

This happened to be a compiler issue. I was recompiled pre-built application and caused the issue. If I left the pre-built application alone and only recompiled certain files, it worked fine.

This issue can be closed.

[igorpadykov]

Hi Jon

nxp does not officially supports rs485 in its bsps, however one can look at below

link with good overview of possible issues:

https://community.nxp.com/thread/499630 

Best regards
igor
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[neuro]

Igor,

Are you implying I need to add the marked and space parity bits in a kernel patch to get it working which will remove the extra 0x00 bytes that are being sent out?

I don't use parity bit currently when sending/receiving.

Thanks,

Jon

[igorpadykov]

Hi Jon

one can try these patches.

Best regards
igor