CC2640R2F-Q1: The specification of HCI_EXT_SetLocalSupportedFeaturesCmd when Slave Latency enabled

Satoshi Shinohara

Part Number: CC2640R2F-Q1

I'm using SDK v2.40.00.32 with BLE v4.2.

When GATT write command is sent from the master to the slave, it seems that the slave ignores the command (or not responds) during Slave Latency interval.

It's not depend on the configuration by HCI_EXT_SetFastTxResponseTimeCmd() function.

Its specification is described below:

The default system value for this feature is HCI_EXT_ENABLE_FAST_TX_RESP_TIME. When the Host transmits data, the controller (by default) ensures the packet is sent over the LL connection with as little delay as possible, even when the connection is configured to use slave latency. That is, the transmit response time will tend to be no longer than the connection interval.

I think that this configuration influences the response time at the first Slave Latency interval ends after GATT write command is sent.

Is that right?

Best Regards,

Satoshi Shinohara

over 6 years ago

0 J Lindh over 6 years ago

TI__Guru 57865 points

Hello Satoshi-san,

I'm assigning this thread internally for follow-up.

0 Marie H over 6 years ago

TI__Guru* 82271 points

Hi Satoshi,

When using slave latency, the slave will not receive the master packets for as long as the slave latency * the connection interval. The master device will know that the packet has not been received by the slave and will re-send it until the slave has received it.

In your case, the master device is sending a GATT write request, but the slave device will not receive it until slave latency has expired (regardless of whether you use HCI_EXT_ENABLE_FAST_TX_RESP_TIME or not).

If you're using HCI_EXT_ENABLE_FAST_TX_RESP_TIME, the slave will wake up on the first connection event aft it has finished processing the GATT write request and send the GATT write response.

If you're not using HCI_EXT_ENABLE_FAST_TX_RESP_TIME, the slave will not necessarily wake up on the next connection event after finishing processing the GATT write request, it will wait for all the slave latency events to pass from the last conenction event it attended.

So yes, using HCI_EXT_ENABLE_FAST_TX_RESP_TIME will give you a lower latency for the GATT write exchange, but not using slave latency will give you an even lower latency.