RemdesKVM/usbkvm/usbkvm_fw2/usbkvm_fw2.ino

/*
  RemdesKVM USB-KVM
  Firmware for PCB design v4 or above

  Author: tobychui

  Upload Settings
  CH552G  
  24Mhz (Internal)
*/

#include <Serial.h>

// Simple mapping: A-Z → HID code 0x04 - 0x1D
uint8_t asciiToHID(char c) {
    if (c >= 'A' && c <= 'Z') return (c - 'A') + 0x04;
    if (c >= 'a' && c <= 'z') return (c - 'a') + 0x04;
    return 0x00;
}

// Checksum = sum of all bytes except last
uint8_t calcChecksum(uint8_t* data, uint8_t len) {
    uint8_t sum = 0;
    for (uint8_t i = 0; i < len; i++) sum += data[i];
    return sum;
}

//Wrapper for writing an array to serial
void Serial0_writeBuf(const uint8_t* data, uint8_t len) {
    for (uint8_t i = 0; i < len; i++) {
        Serial0_write(data[i]);
    }
}

void sendKeyPress(char key) {
    uint8_t packet[] = {
        0x57, 0xAB, 0x00, 0x02, 0x08, // Header, addr, CMD, len
        0x00, 0x00, asciiToHID(key), 0x00, 0x00, 0x00, 0x00, 0x00,
        0x00 // checksum placeholder
    };
    packet[13] = calcChecksum(packet, 13);
    Serial0_writeBuf(packet, 14);
}

void sendKeyRelease() {
    uint8_t packet[] = {
        0x57, 0xAB, 0x00, 0x02, 0x08,
        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
        0x00 // checksum placeholder
    };
    packet[13] = calcChecksum(packet, 13);
    Serial0_writeBuf(packet, 14);
}

void setup() {
    USBSerial_println("Ready. Type a letter to send to CH9329.");

    Serial0_begin(9600); // CH9329 UART default baud
}

void loop() {
    if (USBSerial_available()) {
        char c = USBSerial_read();

        if (asciiToHID(c)) {
            USBSerial_print("Sending key: ");
            USBSerial_println((char)c);

            sendKeyPress(c);
            delay(50);
            sendKeyRelease();
        } else {
            USBSerial_print("Unsupported char: ");
            USBSerial_println((int)c);  // show ASCII code for debugging
        }
    }

    // Echo UART response from CH9329 to USB
    while (Serial1_available()) {
        uint8_t b = Serial1_read();

        USBSerial_print("CH9329 >> 0x");
        if (b < 0x10) USBSerial_print("0");
        USBSerial_println(b, HEX);
    }

}