Why does CBCentralManager report "Peer removed pairing information" with 1st phone after 2-CodePudding

Background

I'm using a couple of different hobbyist BLE devices (HM-10). This particular one is an

The device works great. I have it set to Type 3 which forces it to pair/bond (so iphone or ipad will force you to enter the 6-digit PASS code, which I've set on the device.

iPhone App Works

I have written a simple Single-View iOS app which runs on my iphone / ipad and finds local BLE peripherals.
Everything works great. When I select the item (HM-10) shown above by name I see the iOS pairing dialog & successfully pair the item.

I can send data and everything works fine. If I go out of distance or turn off bluetooth on my device then come back into proximity or turn the device back on, then the iphone can send data again and I see it in the Serial Monitor. Works great.

** The Problem ** The problem occurs if I then pair this device with any other iphone or ipad. After that, the new iphone / ipad can send data to the device with no problem.

However, if I then go back to my original iphone and attempt to send data again, I see the following error raised by the CBCentralManager: "Peer removed pairing information."

After that, I cannot send data from the original iphone to the device again, unless I go to Bluetooth settings on the phone and say, "Forget this device".

Android & HC-06 Bluetooth Devices

I've developed simple Android apps which use a similar Bluetooth classic device (HC-06) and I could pair multiple devices.

Questions

Does BLE 4.0 Allow multiple devices to be paired & bonded?

Do you know why the Peripheral would remove the pairing info? (again, this only occurs if I pair the device with a new iphone / ipad).

Is there a way to send something via iOS app that would tell it to renew the pairing information?

Do you have any suggestions (code to try or other) that would allow me to definitively know that this device does or does not allow multiple phones to pair with it? (I've contacted the manufacturer also.)

Note: I also have a another BLE device here and it seems to exhibit the same behavior. This seems odd though, because I have a BLE speaker that will pair with multiple devices so it must be possible. And I understand that could depend upon the BLE hardware.

CodePudding user response：

Does BLE 4.0 Allow multiple devices to be paired & bonded?

Sure. But that doesn't mean that the device does. It needs to allocate memory for it, and smaller devices often don't.

Do you know why the Peripheral would remove the pairing info? (again, this only occurs if I pair the device with a new iphone / ipad).

It doesn't remove the pairing info. It's telling you the device has removed the pairing info. Pairing info includes a shared secret, so if one side throws away their secret, there's no point in you keeping yours. You have to create a new one.

Is there a way to send something via iOS app that would tell it to renew the pairing information?

Unfortunately no. Apple doesn't give any access to the pairing experience.

There isn't any standardized way to ask devices this kind of information. Some devices support a single pairing Some support two. Some support "a few." But it's really up to the device.

It is very possible that you will get a better overall experience with a Bluetooth 4.1 or 4.2 device, because they've added better security protocols. With iOS 13, the phone also supports cross-transport key derivation, which possibly will help here (if the device also supports it). But I don't think you can improve things with a Bluetooth 4.0 device.