Why 250 ms interval between subsequent reads?

RE: Why 250 ms interval between subsequent reads?

bjorn-spockeli — Tue, 16 May 2017 12:15:45 GMT

I am not familiar with how the MBED OS uses our SDK, so there might be some "bootlenecks" there, but if they've implemented it correctly then you should see the throughput that we list in the SoftDevice Product Specification, Chapter 18, here is the link to the SDS.

RE: Why 250 ms interval between subsequent reads?

HeS — Tue, 16 May 2017 07:44:59 GMT

I'm using MBED OS v5.3 (SDK v12.x) with SoftDevice S132 v2.0.1. Probably the best "strategy" is to wait for software update to SDK v13 and newer SD. I see that such upgrade is prepared.

RE: Why 250 ms interval between subsequent reads?

bjorn-spockeli — Mon, 15 May 2017 12:18:56 GMT

And the "Wait for bucket (off=xx) st=0x0" entries? Which SDK and SoftDevice version are you using?

RE: Why 250 ms interval between subsequent reads?

HeS — Mon, 15 May 2017 12:09:04 GMT

@BS:"Are you calling sd_ble_gattc_read immediately when you get the BLE_GATTC_EVT_READ_RSP event?" YES. I can delay read with EventQueue but i think is not necessary. Status after read is ZERO, so no error in read.

RE: Why 250 ms interval between subsequent reads?

HeS — Mon, 15 May 2017 12:07:05 GMT

@Bjørn Spockeli:"How are you handling the BLE_GATTC_EVT_READ_RSP event?" I have my own callback function (processOnRead). This function copy received fragment to buffer and executed next read command.

RE: Why 250 ms interval between subsequent reads?

bjorn-spockeli — Mon, 15 May 2017 12:04:10 GMT

Could you explain the "Wait for bucket (off=xx) st=0x0" entries? Are you calling sd_ble_gattc_read immediately when you get the BLE_GATTC_EVT_READ_RSP event?

RE: Why 250 ms interval between subsequent reads?

HeS — Mon, 15 May 2017 11:50:04 GMT

Explanation to logs: Receiver (central) send custom frame with command (in log "INFO;") and wait for response (sender). Sender (peripheral) receive command, execute and set response in read characteristic. Receiver read characteristic (128 byte long).

Log is completed in RAM buffer and displayed after end of transaction.

RE: Why 250 ms interval between subsequent reads?

bjorn-spockeli — Mon, 15 May 2017 11:49:17 GMT

I was referring to a Wireshark trace from nRF Sniffer so that we can see how many packets that are sent per connection interval. How are you handling the BLE_GATTC_EVT_READ_RSP event?

RE: Why 250 ms interval between subsequent reads?

HeS — Mon, 15 May 2017 11:43:17 GMT

Receiver log second half:

  0:39:845 Wait for bucket (off=44) st=0x0
  0:40:095 BLE-data (off=44, len=22) bodyLen:119
  0:40:095 Incomplete packet.Fragment: 66 != (119 + 9)
  0:40:095 Wait for bucket (off=66) st=0x0
  0:40:345 BLE-data (off=66, len=22) bodyLen:119
  0:40:345 Incomplete packet.Fragment: 88 != (119 + 9)
  0:40:345 Wait for bucket (off=88) st=0x0
  0:40:595 BLE-data (off=88, len=22) bodyLen:119
  0:40:595 Incomplete packet.Fragment: 110 != (119 + 9)
  0:40:595 Wait for bucket (off=110) st=0x0
  0:40:845 BLE-data (off=110, len=18) bodyLen:119
  0:40:845 BLE-packet completed (ftype:1) btype:0, len:119
  0:41:095 Disconnected for connection 0
  0:49:414 UART-Request 'log'

RE: Why 250 ms interval between subsequent reads?

HeS — Mon, 15 May 2017 11:42:19 GMT

Receiver log. First half (comment limits:)

  0:36:428 UART-Request 'ble.send'
  0:36:429 Setting BLE parameters err_code:0
  0:36:429 PA LNA setting: 0
  0:36:429 Prefered params(st:0): min:30 max:100 latency:0 timeout:400
  0:36:430 UART-Init bucket 1 chunks, 5 chars in queue. 0 in buffer 
  0:36:966 Connection for device 0 status: 0  (state : 0)
  0:37:968 Connection Callback (6 Tx buffers available)
  0:39:095 Terminated SD for handle 0.
  0:39:095 Send command 'info;' for connection 0
  0:39:595 BLE-data (off=0, len=22) bodyLen:119
  0:39:595 FRAME sNode:2 seq:0 dNode:0 fType:1 bLen:119 bType:0
  0:39:595 FRAME body: '?=========== ?'
  0:39:595 Incomplete packet.Fragment: 22 != (119 + 9)
  0:39:596 Wait for bucket (off=22) st=0x0
  0:39:845 BLE-data (off=22, len=22) bodyLen:119
  0:39:845 Incomplete packet.Fragment: 44 != (119 + 9)

RE: Why 250 ms interval between subsequent reads?

HeS — Mon, 15 May 2017 11:38:45 GMT

Ok. Sender log:

  0:06:151 Setting BLE parameters err_code:0
  0:06:151 PA LNA setting: 0
  0:06:151 Prefered params(st:0): min:30 max:100 latency:0 timeout:400
  0:06:152 UART-Init bucket 1 chunks, 15 chars in queue. 0 in buffer 
  0:19:233 Connect: AdrType:1 Addr:49436555FAF8 ownAddr:B272939FDAD5
  0:19:233 Connection Callback (7 Tx buffers available)
  0:20:484 BLE-data (off=0, len=14) bodyLen:5
  0:20:484 FRAME sNode:1 seq:0 dNode:0 fType:1 bLen:5 bType:0
  0:20:484 FRAME body: 'info;'
  0:20:484 BLE-packet completed (ftype:1) btype:0, len:5
  0:20:485 BLE-Request 'info'
  0:20:486 BLE-Init bucket 1 chunks, 462 chars in queue. 0 in buffer 
  0:20:487 FRAME sNode:2 seq:0 dNode:0 fType:1 bLen:119 bType:0
  0:20:487 FRAME body: '?=========== System statistics ========='
  0:20:488 BLE-set response (2) 128 length. Status:0
  0:22:359 BLE-disconnection reason: 0x13

RE: Why 250 ms interval between subsequent reads?

bjorn-spockeli — Mon, 15 May 2017 11:19:11 GMT

It would be very helpful if you could upload a sniffer trace of the transaction.

RE: Why 250 ms interval between subsequent reads?

HeS — Mon, 15 May 2017 08:58:59 GMT

I set on both side the same connection parameters (with sd_ble_gap_ppcp_set):

min:30,  
max:100,  
latency:0,  
timeout:400

and set on both side the same behavior strategy to BLE_CONN_BW_HIGH (6 Tx/Rx buffers in Central and 7 Tx on Peripheral) by this snippet:

//-----------------
...
    if(role == 2)
    	conn_bw.role = BLE_GAP_ROLE_CENTRAL;
    else
    	conn_bw.role = BLE_GAP_ROLE_PERIPH;
    conn_bw.conn_bw.conn_bw_rx = BLE_CONN_BW_HIGH;
    conn_bw.conn_bw.conn_bw_tx = BLE_CONN_BW_HIGH;
    ble_opt.common_opt.conn_bw = conn_bw;
    sd_ble_opt_set(BLE_COMMON_OPT_CONN_BW, &ble_opt)
...
//-----------------

I find only one place in SDK documentation where 250 ms interval is analysed. (SysTick driver settings, 24-bit counter on 64MHz clock overflows every ~250 ms).

RE: Why 250 ms interval between subsequent reads?

RK — Sun, 14 May 2017 22:54:44 GMT

well what are your connection parameters set to for that connection? You get to choose the max and min intervals when you make the connection, what did you choose? If you chose 250ms then that's why you're getting 250ms