Open Source Solution: V3S-PI – Portable Terminal Based on Allwinner V3S

git clone https://gitee.com/fhcloud/uboot-v3scd uboot-v3smake v3s_pi_defconfigmake

git clone https://gitee.com/fhcloud/linux-v3scd linux-v3smake v3s_pi_defconfigmake

git clone https://gitee.com/fhcloud/buildroot-v3s.gitcd buildroot-v3smake v3s_pi_defconfigmake

Main Control Part

The main control of this project uses Allwinner V3S, and it should be noted that R3/R5 resistors should use 1%, and there are two sets of voltages for EPHY.

Figure 1 Main Control Schematic

②ADC Keys

The board has four ADC keys, with a voltage span of 0.2V, implemented through voltage divider resistors.

Figure 2 ADC Keys

③2×16 PIN Expansion Interface

This is achieved through pin headers, leading out 8 expansion interfaces, including a serial port/a I2C bus, which can be used for connecting other devices.

Figure 3 Expansion Interface

④Auxiliary Power Supply

The board has four power supply chips that generate 3.0V, 3.3V, 1.8V, 1.2V, among which

• 3.0V is used for PLL and AVCC analog power supply
• 3.3V is responsible for chip IO and other peripheral power supply
• 1.8V is used for memory power supply
• 1.2V is used for V3S core main control power supply.

Three paths of DCDC have a maximum output current of 2A.

⑤WIFI Module

The board has a 2.4G WIFI module, using the RTL8723BS module, and the connection between V3S and the WIFI module isvia SDIO interface, leading out one IPEX interface for external antenna, R20-R27 are pull-up resistors required by SDIO and the chip, C50/C51/C70 are peripheral filter capacitors, and the module uses 3.3V power supply.

Figure 5 WIFI Module Schematic

⑥10M/100M Ethernet Interface

Fast Ethernet requires the use of two sets of differential pairs, RX/TX differential respectively.Ethernet PHY generally has automatic flip function, so RX/TX can be swapped.The V3S Ethernet uses voltage drive, just need to add a 100NF capacitor to ground at the center tap of the transformer on the network port.

The internal packaged resistors and 2KV capacitors are used to discharge the motherboard’s static electricity, preventing high voltage from damaging the main control chip.

R28/R29 are LED current limiting resistors, SH1 SH2 are the shell, which can be directly grounded.

Figure 6 Ethernet Interface Schematic

⑦2.4-inch LCD Color Screen

The 2.4-inch color screen communicates with the main control via SPI.

• PE8 connects to the color screen reset line
• PE9 connects to DC

Used to distinguish data/instruction.

LEDA is the backlight anode, LEDK connects to Q1 MOS, used for main control to control backlight switch.

The screen is soldered onto the PCB.

Figure 7 2.4-inch LCD Screen Schematic

⑧CH340 Serial to USB

Using the CH340N chip, achieving serial to USB, for computer connection to the terminal.

R30/R31 are used to ensure that the dual-headed TYPEC cable powers normally, D1 is a TVS, to protect the USB interface, since this part uses 3.3V power supply, CH340N’s VCC and V3 need to be connected together, and add 100nf capacitor.

Figure 8 CH340 Serial to USB

⑨CH334R 1-to-4 USB HUB

Through the CH334R chip, achieving one to four USB Host ports.

This part uses unified power supply, so VDD33 and V5 can be connected together.

• XI XO input 12Mhz crystal oscillator

• DPU/DMU connects to upstream USB port

⑩Headphone Interface

The headphone interface uses PJ-342 interface, with audio and recording:

Figure 10 PJ-342 Headphone Interface

⑪SD Card Interface

The SD card interface is used for inserting MicroSD cards.

R32-R36 are pull-up resistors for the SD card, and here CLK does not need to be pulled up, otherwise it may affect SDIO communication.

Figure 11 SD Card Interface

The software solution mainly covers these 8 parts

——Linux kernel, 2.4-inch LCD color screen driver, USB, Ethernet, wireless network card RTL8723BS, ADC keys, audio playback, libcurl.

①Linux Kernel

②2.4-inch LCD Color Screen Driver

The LCD color screen connects to the main control via SPI.

• Software part uses TinyDRM, compared to traditional fbtft, it is no longer fixed frame rate refresh.
• Uses DRM architecture, which can integrate with new architecture programs faster.

Since each manufacturer’s screen initialization code is different, we only need to modify the code in the st7735r_pipe_enable function based on the original st7735r.c file.

The modified code can be referenced in the file below, device tree configuration reference:

&spi0 {       status = "okay";       pinctrl-names = "default";       pinctrl-0 = <&spi0_pins>;

       display@0 {        compatible = "jianda,jd-t18003-t01";        reg = <0>;           spi-max-frequency = <95000000>;

        backlight = <&panel_backlight>;        dc-gpios = <&pio 4 9 0>; // PE9        reset-gpios = <&pio 4 8 0>; // PE8        rotation = <0>;    };};

panel_backlight: panel-backlight {              compatible = "gpio-backlight";        gpios = <&pio 4 7 GPIO_ACTIVE_HIGH>; // PE7              default-on;              status = "okay";       };

&usb_otg {       dr_mode = "host"; // peripheral       status = "okay"};

&usbphy {       status = "okay"};

soc {              ehci0: usb@01c1a000 {                     compatible = "allwinner,sun8i-v3s-ehci", "generic-ehci";                     reg = <0x01c1a000 0x100>;                     interrupts = <GIC_SPI 72 IRQ_TYPE_LEVEL_HIGH>;                     clocks = <&ccu CLK_BUS_EHCI0>, <&ccu CLK_BUS_OHCI0>;                     resets = <&ccu RST_BUS_EHCI0>, <&ccu RST_BUS_OHCI0>;                     status = "okay";              };

              ohci0: usb@01c1a400 {                     compatible = "allwinner,sun8i-v3s-ohci", "generic-ohci";                     reg = <0x01c1a400 0x100>;                     interrupts = <GIC_SPI 73 IRQ_TYPE_LEVEL_HIGH>;                     clocks = <&ccu CLK_BUS_EHCI0>, <&ccu CLK_BUS_OHCI0>,                     <&ccu CLK_USB_OHCI0>;                     resets = <&ccu RST_BUS_EHCI0>, <&ccu RST_BUS_OHCI0>;                     status = "okay";              };       };

④Ethernet

Directly reference the emac node in the DTSI file, device tree reference:

&emac {       allwinner,leds-active-low;       status = "okay"};

&mmc1 {       broken-cd;       bus-width = <4>;       vmmc-supply = <&reg_vcc3v3>;       status = "okay"};

[root@buildroot ~]# cat conn.shmodprobe r8723bs.kowpa_supplicant -B -i wlan0 -c /etc/wpa_supplicant.confudhcpc -i wlan0

ctrl_interface=/var/run/wpa_supplicantap_scan=1

network={        ssid="###############"        psk="###############"}

After adjustment, type mpv filename –no-video, insert headphones, and you can play music:

[root@buildroot ~]# mpv 2.flac --no-video     Video --vid=1 [P] (mjpeg 500x500 1.000fps) (+) Audio --aid=1 (flac 2ch 48000Hz)File tags: Album: 西厢寻他 Title: 西厢寻他 Track: 1AO: [alsa] 48000Hz stereo 2ch s32A: 00:00:04 / 00:03:43 (2%)

Exiting... (Quit)

export PS1='[\