Question

请，我需要任何帮助来解决我的问题。我无法使用HCE在Android（4.4.2）手机和Arduino之间通过NFC模块正常交换数据。
我从Android示例中获取了示例，并略微更改为仅返回IMEI编号。

public byte[] processCommandApdu(byte[] commandApdu, Bundle extras) {
    if (Arrays.equals(SELECT_APDU, commandApdu)) {
        String data = ((TelephonyManager)getSystemService(Context.TELEPHONY_SERVICE)).getDeviceId();
        return ConcatArrays(data.getBytes(), SELECT_OK_SW);
    } else {
        return UNKNOWN_CMD_SW;
    }
}

在Arduino方面，我的代码是：

void loop(){
    Serial.println("Waiting for an ISO14443A card");
    uint8_t success;

    success = nfc.inListPassiveTarget();
    if(success){
        Serial.println("Found something!");      
        uint8_t responseLength = 32;
        uint8_t response[32];
        uint8_t selectApdu[] = { 
             0x00, /* CLA */
             0xA4, /* INS */
             0x04, /* P1  */
             0x00, /* P2  */
             0x05, /* Length of AID  */
             0xF2, 0x22, 0x022, 0x22, 0x22, /* AID */
             0x00  /* Le  */};

        success = nfc.inDataExchange(selectApdu, sizeof(selectApdu), response, &responseLength);
        Serial.print("EX_RES:");
        Serial.println(success);

        if(success) {
            Serial.print("responseLength: "); 
            Serial.println(responseLength);
            for(int i=0; i<responseLength; i++){
                Serial.print(response[i]);
                Serial.print(", ");
            }
            Serial.println();
            Serial.println("========================");
        }
        else {
            Serial.println("Failed sending SELECT AID"); 
        }
    }
    else {
        Serial.println("Didn't find anything!");
    }

    delay(1000);
}

最初，我收到“发送SELECT AID失败”，所以我试图找出原因。所以我在 PN532.cpp 文件中更新了 inDataExchange 的代码。所以现在它看起来像这样：

// initially function was returning bool
uint8_t PN532::inDataExchange(uint8_t *send, uint8_t sendLength, uint8_t *response, uint8_t *responseLength){

uint8_t i;
pn532_packetbuffer[0] = 0x40; // PN532_COMMAND_INDATAEXCHANGE;
pn532_packetbuffer[1] = inListedTag;

if (HAL(writeCommand)(pn532_packetbuffer, 2, send, sendLength)) {
    return 2; // initially was false
}

int16_t status = HAL(readResponse)(response, *responseLength, 1000);
if (status < 0) {
    return 3;  // initially was false
}

if ((response[0] & 0x3f) != 0) {
    DMSG("Status code indicates an error\n");
    return 4;  // initially was false
}

uint8_t length = status;
length -= 1;

if (length > *responseLength) {
    length = *responseLength; // silent truncation...
}

for (uint8_t i = 0; i < length; i++) {
    response[i] = response[i + 1];
}
*responseLength = length;

return 5;  // initially was true
}

现在，我收到了这样的日志输出：

Waiting for an ISO14443A card
Found something!
EX_RES:5
responseLength1: 18
35, 51, 53, 55, 50, 52, 54, 48, 53, 52, 49, 57, 50, 55, 49, 57, 144, 0, 
========================
Waiting for an ISO14443A card
Found something!
EX_RES:4
responseLength1: 32
11, 51, 53, 55, 50, 52, 54, 48, 53, 52, 49, 57, 50, 55, 49, 57, 144, 0, 0, 36, 0, 0, 3, 5, 17, 2, 117, 0, 194, 1, 6, 7, 
========================
Waiting for an ISO14443A card
Found something!
EX_RES:4
responseLength1: 32
1, 51, 53, 55, 50, 52, 54, 48, 53, 52, 49, 57, 50, 55, 49, 57, 144, 0, 0, 36, 0, 0, 3, 5, 17, 2, 117, 0, 194, 1, 6, 7, 
========================
Waiting for an ISO14443A card
Found something!
EX_RES:4
responseLength1: 32
11, 51, 53, 55, 50, 52, 54, 48, 53, 52, 49, 57, 50, 55, 49, 57, 144, 0, 0, 36, 0, 0, 3, 5, 17, 2, 117, 0, 254, 0, 0, 0, 
========================

我知道这个结果是不正确的，并且值是不变的缓冲区（因为错误），除了第一个数字，它会不时变化。
有时我收到这样奇怪的日志：

EX_RES:4
responseLength: 18
11, 219, 13, 51, 8, 187, 181, 0, 2, 54, 1, 1, 2, 140, 0, 7, 72, 1, 
EX_RES:4
responseLength: 18
1, 72, 1, 2, 37, 0, 4, 228, 4, 160, 4, 168, 7, 236, 2, 138, 50, 0,

有什么问题？也许有人遇到过这个问题？也许库存在一些问题，或者我做错了什么？
我正在使用：

Elechouse NFC Module v2.0
Arduino UNO SMD R3
来自https://github.com/elechouse/PN532

Answer 1

我终于开始工作了。首先要说的是问题出现是因为我在Android编程中无能（我完全是新手）。

responseLength必须手动设置，理想情况下，必须等于响应缓冲区大小（感谢来自arduino论坛的Traveller99）
如果屏幕关闭，HCE将无效（这是有趣的部分:)）

当设备的屏幕关闭时，当前的Android实施方案会完全关闭NFC控制器和应用程序处理器。因此，当屏幕关闭时，HCE服务将不起作用。但是，HCE服务可以在锁定屏幕上运行。

感谢Michael尝试提供帮助！

使用HCE，无法通过NFC模块在Android手机和Arduino之间交换数据

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