javascript - BLE 主机 : scanning while connected

Question

基本上我的问题与BLE peripheral: scanning while connected非常相似，只是我指的是主机而不是外围设备。

如果主机已经连接到一个或多个外围设备，它是否仍然能够扫描其他进行广告的外围设备？

我也在使用 bleno 作为外设，使用 noble 作为主控，但我认为这个问题的答案不依赖于实际的模块，而是蓝牙低功耗规范，是吗？

Answer 1

是的，中央可以在与其他外围设备建立连接时进行扫描。请注意，单个外围设备在连接到中央设备时可能会停止广播。这可能会在测试时增加困惑。

这是一个使用 noble 的最小演示:

var noble = require('noble');
var connectedIDs = {};

noble.on('stateChange', (state) => {
  if (state == 'poweredOn') {
    noble.startScanning([], true);
  }
});

noble.on('discover', (peripheral) => {
  if (connectedIDs[peripheral.id] == 'known') {
    console.log(new Date() + ' ' + peripheral.id + ' discovered again');
  } else {
    console.log(new Date() + ' ' + peripheral.id + ' discovered first time')
    connectedIDs[peripheral.id] = 'known';
    // periodically connect to the same peripheral so we get the error
    // message telling us that we are already connected
    setInterval( () => {
      peripheral.connect( (err) => {
        if (err) {
          console.log(new Date() + ' ' + peripheral.id + ' ' + err);
          return;
        }
        console.log(new Date() + ' ' + peripheral.id + ' connected');
      });
    }, 1000);
  }
});

此代码示例连接到它发现的所有外围设备，并同时记录它从中接收广告数据的外围设备的 ID。

输出( chop 了一些列和行):

10:51:06 8652... Error: Peripheral already connected
10:51:06 567b... Error: Peripheral already connected
10:51:06 f0ba... Error: Peripheral already connected
10:51:06 d095... Error: Peripheral already connected
10:51:06 3800... Error: Peripheral already connected
10:51:07 6c20... discovered first time
10:51:07 f0ba... Error: Peripheral already connected
10:51:07 d095... Error: Peripheral already connected
10:51:07 3800... Error: Peripheral already connected
10:51:07 6c20... discovered again
10:51:08 8652... Error: Peripheral already connected
10:51:08 567b... Error: Peripheral already connected
10:51:08 f0ba... Error: Peripheral already connected
10:51:08 6c20... discovered again
10:51:08 d095... Error: Peripheral already connected
10:51:08 8652... Error: Peripheral already connected
10:51:08 3800... Error: Peripheral already connected
10:51:08 6c20... discovered again
10:51:08 f0ba... Error: Peripheral already connected
10:51:08 d095... Error: Peripheral already connected
10:51:08 3800... Error: Peripheral already connected
10:51:08 6c20... connected
10:51:08 6c20... connected

发生了什么？

当6c20...第一次被发现时，已经有多个外设连接到noble。重复连接尝试的错误消息显示外围设备在扫描时仍处于连接状态。在我的示例运行中，我连接了 6 个 BLE 外设，6c20... 是第 7 个加入的。我在 2015 年中期使用 OS X 10.11.3 的 MacBookPro 上使用了 noble v1.3.0 和 node v4.2.4。

这没有回答第二个问题:此行为是否取决于实际模块或蓝牙低功耗规范？

据我所知，BLE 规范没有指定中央必须支持的连接数量。 AFAIK 因为 BLE 核心规范相当大，所有对同时和多个连接的引用我都可以找到它取决于实现的状态。所以，这似乎完全取决于由硬件和软件组成的BLE产品。即使 BLE 规范会指定它，我也更愿意查看产品的数据表。此外，它也取决于主机上运行的软件。幸运的是，noble 做到了。

举个例子，我们看一下Nordic的Soft Device S120的datasheet:https://www.nordicsemi.com/eng/nordic/download_resource/26275/14/32008006

S120 软设备是 Nordic NRF51 系列 BLE IC(最著名的例子是 nRF51822)的 BLE 堆栈(固件)。

这里引用上面链接的数据表:

The SoftDevice supports eight concurrent master connections and an additional Scanner/Initiator role. When the maximum number of simultaneous connections are established, the Scanner role will be supported for new device discovery though the initiator is not available at that time.