Negociate new "connection parameters" from low to high speed

Question

Dear Nordic Developer Zone, 
 I have modified the ble_conn_params.c file in order to be able to negotiate new connections speeds between IOS app and Nordic nRF51822 chip on demand. It is working well, but only from high to low communication speed between devices. 
 The target is to have the lowest current consumption possible with a low communication speed during standard processes (95% of the usage), and switch to a high communication speed during configuration and update processes, then switch back to the low communication speed. 
 The default connection params working with the chip are: 
 //Default IOS params
#define MIN_CONN_INTERVAL 24 //(1.25ms) = 30 ms
#define MAX_CONN_INTERVAL 24 //(1.25ms) = 30 ms
#define SLAVE_LATENCY 0 //(1.25ms) = 0 ms 
#define CONN_SUP_TIMEOUT 72 //(10ms) = 720 ms
 
 I am able to negociate a lower speed communication with these params 
 //Low speed comm
#define MIN_CONN_INTERVAL 24 //(1.25ms) = 30 ms
#define MAX_CONN_INTERVAL 50 //(1.25ms) = 62.5 ms
#define SLAVE_LATENCY 4 //(1.25ms) = 5 ms 
#define CONN_SUP_TIMEOUT 550 //(10ms) = 5.5 s
 
 But, when IOS and Nordic chip are using these params, I can't set the default params anymore. The negotiation failed. 
 Is there any limitation to switch from low speed conn params to high speed conn params? 
 I am using nRF51822 with Softdevice. 
 Best regards

Pål Håland · Accepted Answer

Hi Sébastien 
 if you have a look at the developer.apple.com/.../BluetoothDesignGuidelines.pdf and read the section about Connection Parameters. 
 
 Connection Parameters
The Bluetooth accessory is responsible for the connection parameters used for the LE connection. The accessory should request connection parameters appropriate for its use case by sending an L2CAP Connection Parameter Update Request at the appropriate time. See the Bluetooth 4.0 specification, Volume 3, Part A, Section 4.20 for details. 
 The connection parameter request may be rejected if it does not comply with all of these rules:
Interval Max * (Slave Latency + 1) ≤ 2 seconds
Interval Min ≥ 20 ms
 Interval Min + 20 ms ≤ Interval Max 
Slave Latency ≤ 4
connSupervisionTimeout ≤ 6 seconds
Interval Max * (Slave Latency + 1) * 3 < connSupervisionTimeout 
 The Apple product will not read or use the parameters in the Peripheral Preferred Connection Parameters characteristic. See the Bluetooth 4.0 specification, Volume 3, Part C, Section 12.5. 
 
 The default ones will be rejected because MIN_CONN_INTERVAL == MAX_CONN_INTERVAL

Negociate new "connection parameters" from low to high speed

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