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UART Driver Debugging Guide

The S100(S600) chip has a total of 4(8) UARTs, namely uart0-uart3(uart0~uart7). Among them, uart0 is used as the debug console, DMA is not enabled by default, and the baud rate is determined by controlling the Bootstrip pin to be either 115200 or 921600.

The other UARTs are used for data transmission, with DMA enabled by default in the device tree. They support various baud rates configured via software, with the commonly used baud rate being 921600. uart0 and uart1 support hardware flow control, while the other UARTs do not support this feature.

UART Usage Instructions​

Code Path​

drivers/tty/serial/8250/8250_dw.c   # UART driver file
drivers/tty/serial/8250/8250_port.c    # UART port operation file
drivers/tty/serial/8250/8250_core.c    # 8250 UART driver core
hobot-drivers/serial/8250_pdma.c    # UART PDMA operation implementation file

Kernel Configuration​

Configuration file path: hobot-drivers/configs/drobot_s100_defconfig

Configuration file path: hobot-drivers/configs/drobot_s600_defconfig

CONFIG_SERIAL_8250=y   # 8250 driver configuration
CONFIG_SERIAL_8250_CONSOLE=y   # 8250 console driver configuration
CONFIG_SERIAL_8250_DW=y   # Enable Designware-specific features

DTS Device Node Configuration​

/*kernel/arch/arm64/boot/dts/hobot/drobot-s100-soc.dtsi*/
uart1: uart@394A0000 {
    power-domains = <&scmi_smc_pd PD_IDX_LSPERI_TOP>;
    compatible = "snps,dw-apb-uart";
    reg = <0x0 0x394A0000 0x0 0x10000>;
    reg-shift = <2>;
    reg-io-width = <4>;
    interrupts = <GIC_SPI PERISYS_UART0_INTR PERISYS_UART0_INTR_TRIG_TYPE>;
    clock-frequency = <200000000>;
    pinctrl-names = "default";
    pinctrl-0 = <&peri_uart0>;
    dmas = <&pdma0 0>, <&pdma0 1>;
    dma-names = "rx", "tx";
    status = "okay";
};
/*kernel/arch/arm64/boot/dts/hobot/drobot-s600-soc.dtsi*/
uart4: uart@3484E000 {
    // power-domains = <&scmi_smc_pd PD_IDX_LSPERI_TOP>;
    compatible = "snps,dw-apb-uart";
    reg-shift = <2>;
    reg-io-width = <4>;
    reg = <0x0 0x3484E000 0x0 0x10000>;
    interrupts = <GIC_SPI HSISYS_UART4_INTR IRQ_TYPE_LEVEL_HIGH>;
    clock-frequency = <500000000>;
    pinctrl-names = "default";
    pinctrl-0 = <&hsi_uart4_txd_uart4_txd &hsi_uart4_rxd_uart4_rxd>;
    dmas = <&pdma0 8>, <&pdma0 9>;
    dma-names = "rx", "tx";
};

Usage Examples​

Check UART Nodes​

ls /dev/ttyS*
/dev/ttyS0  /dev/ttyS1  /dev/ttyS2  /dev/ttyS3

Serial Port Operations​

  • View serial port baud rate and other configurations:

    stty -F /dev/ttyS1 -a

  • Configure baud rate, etc.:

    stty -F /dev/ttyS1 speed 921600 cs8 -cstopb parenb -parodd

  • Read serial port data:

    cat /dev/ttyS1

  • Test output data to the serial port:

    echo 123456789 > /dev/ttyS1

On RDK S600, uart4 is initialized as /dev/ttyS1. uart4 does not have physical pins exposed and does not support software loopback internally, so serial read/write testing cannot be performed.

Important Notes​

  • In the RDK S100 hardware design, the 40-pin GPIO uses a TXS series level shift chip from TI to convert 1.8V IO to 3.3V IO. For signal quality and reliability, it is recommended that the communication peer avoid using another level shift chip for further conversion. If multiple stages are used, please pay attention to the actual hardware signal quality.
  • In the RDK S600 hardware design, only uart6 and uart7 are exposed via expansion pin headers, and a TXB series level shift chip from TI is used to convert 1.8V IO to 3.3V IO. Due to hardware limitations on the RDK S600 V0P1 development board, uart6 and uart7 cannot be used.
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