CONFIG_BT_MESH_DFD_SRV_TARGETS_MAX questions

[AndyM]

Hello

I've been experimenting in increasing the number of targets that a mesh FOTA distribution server can support on nRF52840

The CONFIG_BT_MESH_DFD_SRV_TARGETS_MAX has a maximum  65535

But for practical purposes I'd be happy if I could have at least 50-60.

Ran into build asserts in zephyr\subsys\bluetooth\mesh\dfd_srv.c

"The Firmware Distribution Receivers List message does not fit into the maximum " "outgoing SDU size"

The comparison is done to the  BT_MESH_TX_SDU_MAX which is built as follows

#define BT_MESH_TX_SDU_MAX        MAX((BT_MESH_TX_SEG_MAX *     \

                       BT_MESH_APP_SEG_SDU_MAX),    \

                      BT_MESH_APP_UNSEG_SDU_MAX)

CONFIG_BT_MESH_TX_SEG_MAX is limited to 32

BT_MESH_APP_SEG_SDU_MAX is defined as 12

BT_MESH_APP_UNSEG_SDU_MAX is defined as 15

By trial and error I was able to set the number of targets to 39 with these configurations

ONFIG_BT_MESH_MSG_CACHE_SIZE=256

CONFIG_BT_MESH_ADV_BUF_COUNT=128

CONFIG_BT_MESH_TX_SEG_MAX=32

CONFIG_BT_MESH_RX_SEG_MAX=32

CONFIG_BT_MESH_TX_SEG_MSG_COUNT=64

CONFIG_BT_MESH_RX_SEG_MSG_COUNT=64

CONFIG_BT_MESH_DFD_SRV_TARGETS_MAX=39

Is this it? Or is there another way to increase the number of supported targets?

Thank you

 

[AndyM]

Please clarify what you mean by "send a few target once at a time"  What commands should I use??

Do you mean I can do
mesh models dfd receivers-add <1,2,3>

mesh models dfd start ...

mesh models dfd receivers-add <4,5.6>

mesh models dfd start ...

??
If that's the case - how long should I wait before sending the next batch?

[Hung Bui]

Please try: 

mesh models dfd receivers-add <1,2,3>

mesh models dfd receivers-add <4,5,6>

mesh models dfd receivers-add <7,8,9>

mesh models dfd start ...

[AndyM]

Set CONFIG_BT_MESH_DFD_SRV_TARGETS_MAX = 70

Set CONFIG_BT_MESH_TX_SEG_MAX = 32

Used method you suggested to add targets in batches of 3

Get the "SDU canceled" error and transfer fails
The error occurs regardless of the number of targets - even with just one.

What triggers it it seems is CONFIG_BT_MESH_TX_SEG_MAX  > 10

So at the moment I'm stuck with 22 targets - maximum possible with CONFIG_BT_MESH_TX_SEG_MAX =10 without getting build asserts.
Please advise

[Hung Bui]

Hi Andy, 
I'm finally back to the office and can actually do some tests. 
I was doing a quick test with NCS v2.9.0 and the default distributor sample. Here is my list of commands:

By default CONFIG_BT_MESH_DFD_SRV_TARGETS_MAX = 8 and CONFIG_BT_MESH_TX_SEG_MAX =10. 

So it seems to works with small number of receiver and multiple dfd receivers-add packet. 

However, when increasing CONFIG_BT_MESH_DFD_SRV_TARGETS_MAX  to 32 I hit what you reported earlier : 

BUILD_ASSERT((DFD_RECEIVERS_LIST_MSG_MAXLEN + BT_MESH_MODEL_OP_LEN(BT_MESH_DFD_OP_RECEIVERS_LIST) +

          BT_MESH_MIC_SHORT) <= BT_MESH_TX_SDU_MAX,

         "The Firmware Distribution Receivers List message does not fit into the maximum "

         "outgoing SDU size.");


So this issue is not about adding the target to the list, it's about that the report of the list can not fit into one mess message (the one what showed 8 target in my screenshot). I will check with the team how should we deal with this problem. My understanding is that this static assert can be modified so that the list can be acquired by multiple message dfd receivers-get message instead of one single message. 
I will keep you updated. 

 

[AndyM]

Yes, I'm using the same commands.
What you're describing is only 1 problem. 
There are actually 3

1. When CONFIG_BT_MESH_DFD_SRV_TARGETS_MAX is increased  the CONFIG_BT_MESH_TX_SEG_MAX must be increased as well otherwise there is a build assert. Might be good to document it somewhere, (The one you describe)

2. Asserts check against BT_MESH_TX_SDU_MAX or BT_MESH_RX_SDU_MAX ( that the values they check are smaller)
However those defines use 2 hard coded values :BT_MESH_APP_SEG_SDU_MAX and  BT_MESH_APP_UNSEG_SDU_MAX (12 and 15 respectively)  - see in zephyr\include\zephyr\bluetooth\mesh\access.h
So even if CONFIG_BT_MESH_TX_SEG_MAX  is increased to 32 the CONFIG_BT_MESH_DFD_SRV_TARGETS_MAX cannot go higher than 70 or so.

3. Increasing CONFIG_BT_MESH_TX_SEG_MAX  to 32 causes DFD to fail almost immediately with "SDU canceled" error even if the number of targets is 1.