For a professional project, i have to use a RPI4 as a central device to connect to a particular peripheral device. For testing, I developped a program to simulate a peripheral on a RPi (thanks to bleno Node.js module) by setting a GATT server and use another RPi as my central with the bluepy Python library.
All worked fine but when I set the advertising interval higher than 4000ms on my peripheral, connection doesn't work anymore (even on the RPi GATT server or with the production one).
I tried to use gatttool/hcitool on my central, same issues, it works well but only if advertising interval is less than 4000ms. But it works when I try to connect to my GATT server with my phone with a dedicated application (nRF connect).
After some research, I found that the Linux kernel only validates values of connection interval within the range 7.5ms - 4000ms (https://lkml.org/lkml/2019/8/2/358), which match exactly with my experimental values. But except if I don't understand something with BLE, connection interval and advertising interval are totally independent and it should not be a problem. In the Bluetooth documentation, I found that maximum advertising interval value should be 10240ms. There is something I don't understand.
Here is my GATT server running on one RPi4 if you want to reproduce that.
I start it using sudo BLENO_ADVERTISING_INTERVAL=xxxx node my_gatt_server.js with xxxx the advertising interval I want in ms.
var bleno = require('bleno');
// Once bleno starts, begin advertising our BLE address
bleno.on('stateChange', function(state) {
console.log('State change: ' + state);
if (state === 'poweredOn') {
bleno.startAdvertising('MyDevice',['6d79686561727473656e74696e656c10']);
} else {
bleno.stopAdvertising();
}
});
// Notify the console that we've accepted a connection
bleno.on('accept', function(clientAddress) {
console.log("Accepted connection from address: " + clientAddress);
});
// Notify the console that we have disconnected from a client
bleno.on('disconnect', function(clientAddress) {
console.log("Disconnected from address: " + clientAddress);
});
// When we begin advertising, create a new service and characteristic
bleno.on('advertisingStart', function(error) {
if (error) {
console.log("Advertising start error: " + error);
} else {
console.log("Advertising start success");
bleno.setServices([
// Define a new service
new bleno.PrimaryService({
uuid : '6d79686561727473656e74696e656c10',
characteristics : [
// ECG characteristic
new bleno.Characteristic({
value : 'hello!',
uuid : '6d79686561727473656e74696e656c11',
properties : ['read'],
// Send a message back to the client with the characteristic's value
onReadRequest : function(offset, callback) {
console.log("Read request received");
callback(this.RESULT_SUCCESS, new Buffer("Echo: " + this.value);
}
})
]
}),
]);
}
});
HCI packets logs
When connection succeeded
Bluetooth monitor ver 5.50
= Note: Linux version 4.19.57-v7l+ (armv7l) 0.501891
= Note: Bluetooth subsystem version 2.22 0.501900
= New Index: xx:xx:xx:xx:xx:xx (Primary,UART,hci0) [hci0] 0.501905
= Open Index: xx:xx:xx:xx:xx:xx [hci0] 0.501908
= Index Info: xx:xx:xx:xx:xx:xx (Cypress Semiconductor Corporation) [hci0] 0.501911
@ MGMT Open: bluetoothd (privileged) version 1.14 {0x0001} 0.501915
@ MGMT Open: btmon (privileged) version 1.14 {0x0002} 0.501989
< HCI Command: LE Set Scan Parameters (0x08|0x000b) plen 7 #1 [hci0] 4.586280
Type: Passive (0x00)
Interval: 60.000 msec (0x0060)
Window: 30.000 msec (0x0030)
Own address type: Public (0x00)
Filter policy: Ignore not in white list (0x01)
> HCI Event: Command Complete (0x0e) plen 4 #2 [hci0] 4.586656
LE Set Scan Parameters (0x08|0x000b) ncmd 1
Status: Success (0x00)
< HCI Command: LE Set Scan Enable (0x08|0x000c) plen 2 #3 [hci0] 4.586717
Scanning: Enabled (0x01)
Filter duplicates: Enabled (0x01)
> HCI Event: Command Complete (0x0e) plen 4 #4 [hci0] 4.587132
LE Set Scan Enable (0x08|0x000c) ncmd 1
Status: Success (0x00)
> HCI Event: LE Meta Event (0x3e) plen 33 #5 [hci0] 4.619942
LE Advertising Report (0x02)
Num reports: 1
Event type: Connectable undirected - ADV_IND (0x00)
Address type: Public (0x00)
Address: xx:xx:xx:xx:xx:xx (OUI DC-A6-32)
Data length: 21
Flags: 0x06
LE General Discoverable Mode
BR/EDR Not Supported
128-bit Service UUIDs (partial): 1 entry
Vendor specific (6d796865-6172-7473-656e-74696e656c10)
RSSI: -31 dBm (0xe1)
< HCI Command: LE Set Scan Enable (0x08|0x000c) plen 2 #6 [hci0] 4.620014
Scanning: Disabled (0x00)
Filter duplicates: Disabled (0x00)
> HCI Event: Command Complete (0x0e) plen 4 #7 [hci0] 4.621661
LE Set Scan Enable (0x08|0x000c) ncmd 1
Status: Success (0x00)
< HCI Command: LE Create Connection (0x08|0x000d) plen 25 #8 [hci0] 4.621724
Scan interval: 60.000 msec (0x0060)
Scan window: 60.000 msec (0x0060)
Filter policy: White list is not used (0x00)
Peer address type: Public (0x00)
Peer address: xx:xx:xx:xx:xx:xx (OUI DC-A6-32)
Own address type: Public (0x00)
Min connection interval: 30.00 msec (0x0018)
Max connection interval: 50.00 msec (0x0028)
Connection latency: 0 (0x0000)
Supervision timeout: 420 msec (0x002a)
Min connection length: 0.000 msec (0x0000)
Max connection length: 0.000 msec (0x0000)
> HCI Event: Command Status (0x0f) plen 4 #9 [hci0] 4.622251
LE Create Connection (0x08|0x000d) ncmd 1
Status: Success (0x00)
> HCI Event: LE Meta Event (0x3e) plen 19 #10 [hci0] 4.726113
LE Connection Complete (0x01)
Status: Success (0x00)
Handle: 64
Role: Master (0x00)
Peer address type: Public (0x00)
Peer address: xx:xx:xx:xx:xx:xx (OUI DC-A6-32)
Connection interval: 48.75 msec (0x0027)
Connection latency: 0 (0x0000)
Supervision timeout: 420 msec (0x002a)
Master clock accuracy: 0x00
@ MGMT Event: Device Connected (0x000b) plen 34 {0x0002} [hci0] 4.726162
LE Address: xx:xx:xx:xx:xx:xx (OUI DC-A6-32)
Flags: 0x00000000
Data length: 21
Flags: 0x06
LE General Discoverable Mode
BR/EDR Not Supported
128-bit Service UUIDs (partial): 1 entry
Vendor specific (6d796865-6172-7473-656e-74696e656c10)
@ MGMT Event: Device Connected (0x000b) plen 34 {0x0001} [hci0] 4.726162
LE Address: xx:xx:xx:xx:xx:xx (OUI DC-A6-32)
Flags: 0x00000000
Data length: 21
Flags: 0x06
LE General Discoverable Mode
BR/EDR Not Supported
128-bit Service UUIDs (partial): 1 entry
Vendor specific (6d796865-6172-7473-656e-74696e656c10)
< HCI Command: LE Read Remote Used Features (0x08|0x0016) plen 2 #11 [hci0] 4.726356
Handle: 64
> HCI Event: Command Status (0x0f) plen 4 #12 [hci0] 4.726943
LE Read Remote Used Features (0x08|0x0016) ncmd 1
Status: Success (0x00)
> HCI Event: Command Complete (0x0e) plen 14 #13 [hci0] 4.726951
LE Read Remote Used Features (0x08|0x0016) ncmd 1
Status: Success (0x00)
00 00 00 00 00 00 00 00 00 00 ..........
> HCI Event: LE Meta Event (0x3e) plen 12 #14 [hci0] 4.881359
LE Read Remote Used Features (0x04)
Status: Success (0x00)
Handle: 64
Features: 0x3f 0x00 0x00 0x00 0x00 0x00 0x00 0x00
LE Encryption
Connection Parameter Request Procedure
Extended Reject Indication
Slave-initiated Features Exchange
LE Ping
LE Data Packet Length Extension
> HCI Event: LE Meta Event (0x3e) plen 11 #15 [hci0] 5.027630
LE Data Length Change (0x07)
Handle: 64
Max TX octets: 251
Max TX time: 2120
Max RX octets: 251
Max RX time: 2120
When connection failed
Bluetooth monitor ver 5.50
= Note: Linux version 4.19.57-v7l+ (armv7l) 0.114663
= Note: Bluetooth subsystem version 2.22 0.114671
= New Index: xx:xx:xx:xx:xx:xx (Primary,UART,hci0) [hci0] 0.114675
= Open Index: xx:xx:xx:xx:xx:xx [hci0] 0.114678
= Index Info: xx:xx:xx:xx:xx:xx (Cypress Semiconductor Corporation) [hci0] 0.114681
@ MGMT Open: bluetoothd (privileged) version 1.14 {0x0001} 0.114686
@ MGMT Open: btmon (privileged) version 1.14 {0x0002} 0.114760
< HCI Command: Disconnect (0x01|0x0006) plen 3 #1 [hci0] 5.864108
Handle: 64
Reason: Remote User Terminated Connection (0x13)
> HCI Event: Command Status (0x0f) plen 4 #2 [hci0] 5.864469
Disconnect (0x01|0x0006) ncmd 1
Status: Success (0x00)
> HCI Event: Disconnect Complete (0x05) plen 4 #3 [hci0] 5.883803
Status: Success (0x00)
Handle: 64
Reason: Remote User Terminated Connection (0x13)
@ MGMT Event: Device Disconnected (0x000c) plen 8 {0x0002} [hci0] 5.883848
LE Address: xx:xx:xx:xx:xx:xx (OUI DC-A6-32)
Reason: Connection terminated by remote host (0x03)
@ MGMT Event: Device Disconnected (0x000c) plen 8 {0x0001} [hci0] 5.883848
LE Address: xx:xx:xx:xx:xx:xx (OUI DC-A6-32)
Reason: Connection terminated by remote host (0x03)
< HCI Command: LE Set Scan Parameters (0x08|0x000b) plen 7 #4 [hci0] 25.059876
Type: Passive (0x00)
Interval: 60.000 msec (0x0060)
Window: 30.000 msec (0x0030)
Own address type: Public (0x00)
Filter policy: Ignore not in white list (0x01)
> HCI Event: Command Complete (0x0e) plen 4 #5 [hci0] 25.060698
LE Set Scan Parameters (0x08|0x000b) ncmd 1
Status: Success (0x00)
< HCI Command: LE Set Scan Enable (0x08|0x000c) plen 2 #6 [hci0] 25.060762
Scanning: Enabled (0x01)
Filter duplicates: Enabled (0x01)
> HCI Event: Command Complete (0x0e) plen 4 #7 [hci0] 25.061665
LE Set Scan Enable (0x08|0x000c) ncmd 1
Status: Success (0x00)
> HCI Event: LE Meta Event (0x3e) plen 33 #8 [hci0] 39.473657
LE Advertising Report (0x02)
Num reports: 1
Event type: Connectable undirected - ADV_IND (0x00)
Address type: Public (0x00)
Address: xx:xx:xx:xx:xx:xx (OUI DC-A6-32)
Data length: 21
Flags: 0x06
LE General Discoverable Mode
BR/EDR Not Supported
128-bit Service UUIDs (partial): 1 entry
Vendor specific (6d796865-6172-7473-656e-74696e656c10)
RSSI: -28 dBm (0xe4)
< HCI Command: LE Set Scan Enable (0x08|0x000c) plen 2 #9 [hci0] 39.473746
Scanning: Disabled (0x00)
Filter duplicates: Disabled (0x00)
> HCI Event: Command Complete (0x0e) plen 4 #10 [hci0] 39.475900
LE Set Scan Enable (0x08|0x000c) ncmd 1
Status: Success (0x00)
< HCI Command: LE Create Connection (0x08|0x000d) plen 25 #11 [hci0] 39.475956
Scan interval: 60.000 msec (0x0060)
Scan window: 60.000 msec (0x0060)
Filter policy: White list is not used (0x00)
Peer address type: Public (0x00)
Peer address: xx:xx:xx:xx:xx:xx (OUI DC-A6-32)
Own address type: Public (0x00)
Min connection interval: 30.00 msec (0x0018)
Max connection interval: 50.00 msec (0x0028)
Connection latency: 0 (0x0000)
Supervision timeout: 420 msec (0x002a)
Min connection length: 0.000 msec (0x0000)
Max connection length: 0.000 msec (0x0000)
> HCI Event: Command Status (0x0f) plen 4 #12 [hci0] 39.476993
LE Create Connection (0x08|0x000d) ncmd 1
Status: Success (0x00)
< HCI Command: LE Create Connection Cancel (0x08|0x000e) plen 0 #13 [hci0] 43.544123
> HCI Event: Command Complete (0x0e) plen 4 #14 [hci0] 43.546763
LE Create Connection Cancel (0x08|0x000e) ncmd 1
Status: Success (0x00)
> HCI Event: LE Meta Event (0x3e) plen 19 #15 [hci0] 43.546914
LE Connection Complete (0x01)
Status: Unknown Connection Identifier (0x02)
Handle: 64
Role: Master (0x00)
Peer address type: Public (0x00)
Peer address: xx:xx:xx:xx:xx:xx (OUI DC-A6-32)
Connection interval: 48.75 msec (0x0027)
Connection latency: 0 (0x0000)
Supervision timeout: 420 msec (0x002a)
Master clock accuracy: 0x00
When it fails, gatttool output error is Error: connect error: Transport endpoint is not connected (107)
4000 ms is a quite large advertising interval. Anyway, bluepy uses BlueZ, and when BlueZ connects, it first scans and when it finds the wanted device, it stops scanning and initiates a connection. During this connection attempt, there is a timeout before starting scanning again. It could be that this 4000 ms advertising interval is larger than the timeout. It's commonly 2 seconds I think.
Please start "sudo btmon" on your central device before attempting to connect, let it capture and print the HCI packets and post the output here.
Advertising interval and Connection interval are completely independent.