CC2640R2F: Set MAX_PDU_SIZE 255 but Payload not 251

Part Number: CC2640R2F

Tool/software:

Hi,

Why I set MAX_PDU_SIZE = 255 I sent packet data 251 bytes, but payload remain 248 and spilt packet not 251 bytes in 1 time

and I try set MAX_PDU_SIZE = 251 I sent packet data 251 bytes, but payload remain 244 and spilt packet not 247 bytes in 1 time

From ATT_MTU=MAX_PDU_SIZE-L2CAP_HDR_SIZE or ATT_MTU(251) = MAX_PDU_SIZE(255) - L2CAP_HDR_SIZE(4) Follow figure below

I found note follow figure below I see about (ATT_MTU-3) bytes results. I don't know if this is related to the problems we're facing right now.

I use CCS version 10.1.1.00004 

software project Simple serial socket Server

Copyright (c) 2020, Texas Instruments Incorporated

SDK: 5.30.1.11

Thank,

Vasu Khwanyuen