Writing characteristics longer than 20 bytes

RE: Writing characteristics longer than 20 bytes

TCdeveloper — Wed, 22 Apr 2020 21:14:45 GMT

Thanks Amanda Hsieh. I guess what I am really asking in my second question is what are the pros/cons of using queued writes vs. simply increasing the MTU size? Increasing the MTU size seems inherently simpler so why would someone choose queued writes for longer transmissions?

RE: Writing characteristics longer than 20 bytes

Amanda Hsieh — Wed, 22 Apr 2020 09:35:06 GMT

Hi,

[quote user="TCdeveloper"]1) How large can I make the MTU size?[/quote]

Start from S132 v3.0 (for nRF52) you can increase the MTU to maximum 512.

[quote user="TCdeveloper"]2) Is there a preferred way to write larger amounts of data (from central to peripheral)?[/quote]

You can refer to the ATT_MTU Throughput Example which uses Queued Write.

-Amanda H.

RE: Writing characteristics longer than 20 bytes

Nguyen Hoan Hoang — Wed, 22 Apr 2020 06:46:01 GMT

251-3 for ble 4.2

512-3 for ble 5

RE: Writing characteristics longer than 20 bytes

TCdeveloper — Tue, 21 Apr 2020 16:15:12 GMT

Thanks Nguyen Hoan Hoang. This is indeed what I needed to do. Any thoughts on the follow-up questions I asked Amanda?

RE: Writing characteristics longer than 20 bytes

TCdeveloper — Tue, 21 Apr 2020 16:14:00 GMT

Amanda Hsieh This was helpful, thanks. It did fix my immediate problem. A couple of follow up questions.

1) How large can I make the MTU size?

2) Is there a preferred way to write larger amounts of data (from central to peripheral)?

For example, others on devzone have mentioned queued (or long) writes. I tried this out by instantiating the "ble_app_queued_writes" example and it also seems to work.

RE: Writing characteristics longer than 20 bytes

Nguyen Hoan Hoang — Tue, 21 Apr 2020 12:01:45 GMT

When you increase the MTU size, softdevice will requires more ram space for that matter. You need to readjust the reserve ram for softdevice as indicated in the log in the linker script.

RE: Writing characteristics longer than 20 bytes

Amanda Hsieh — Tue, 21 Apr 2020 08:27:41 GMT

Hi,

[quote user="TCdeveloper"]<warning> nrf_sdh_ble: Change the RAM start location from 0x20002220 to 0x20002228.
<warning> nrf_sdh_ble: Maximum RAM size for application is 0xDDD8.[/quote]

You need to modify the RAM start location and Maximum RAM size in the project option -> Linker -> Section Placement Marcos as the log indicates.

RE: Writing characteristics longer than 20 bytes

TCdeveloper — Mon, 20 Apr 2020 15:25:44 GMT

Nguyen Hoan Hoang I assume you mean the following #defines:

// <o> NRF_SDH_BLE_GATT_MAX_MTU_SIZE - Static maximum MTU size.
#ifndef NRF_SDH_BLE_GATT_MAX_MTU_SIZE
#define NRF_SDH_BLE_GATT_MAX_MTU_SIZE 24 // Default = 23
#endif

If I change the size greater to anything than the default value of 23, I wind up in the app_err_fault_handler() routine in app_error_weak.c.

Debug terminal warning messages include:

<warning> nrf_sdh_ble: Insufficient RAM allocated for the SoftDevice.
<warning> nrf_sdh_ble: Change the RAM start location from 0x20002220 to 0x20002228.
<warning> nrf_sdh_ble: Maximum RAM size for application is 0xDDD8.
<error> nrf_sdh_ble: sd_ble_enable() returned NRF_ERROR_NO_MEM.
<error> app: Fatal error

Note that I am using SDK 15.0.0 with the nRF52 development kit (if that is helpful).

Thoughts?

RE: Writing characteristics longer than 20 bytes

Nguyen Hoan Hoang — Mon, 20 Apr 2020 06:47:04 GMT

You need to initialize the softdevice with a max mtu value require otherwise the default is 20. look for MTU somewhere in sdk_config.h