Updated Static Buffer Allocation section

wolfSSL/src/chapter04.md

@@ -551,7 +551,10 @@ By default, wolfSSL assumes that the execution environment provides dynamic memo
 
 Using static-buffer-allocation is equivalent in API to using dynamic memory with wolfSSL. This functional equivalency is achieved in wolfSSL by abstracting memory allocation/free into XMALLOC/XFREE function calls. Once static-buffer-allocation is set, wolfSSL will use it from then on to allocate buffers and other structures used internally. Since this feature is set for WOLFSSL_CTX, it will continue to work for the lifetime of the context object.
 
-The static-buffer-allocation set in a WOLFSSL_CTX is thread-safe. Even if the same WOLFSSL_CTX is shared by different threads, buffer allocation/free is used under exclusive control inside wolfSSL.
+The static-buffer-allocation set in a WOLFSSL_CTX is thread-safe. Even if the same WOLFSSL_CTX is shared by different threads, buffer allocation/free is used under exclusive control inside wolfSSL. The following is a visual representation of the CTX structure, the arrows indicate passing a pointer to the heap and "..." references all structs and not to the ones listed.
+
+![Alt text](CTX_structure.png)
+
 In comparison to a memory pool functionality offered by an RTOS implementation, memory functionality in an RTOS will commonly suspend a thread (task) if an unused memory block cannot be found when requested until a free block becomes available. wolfSSL’s static memory functionality has no such synchronization capability.
 
 ### Specifying Static Buffer Use
@@ -582,6 +585,36 @@ user_settings.h
     #define WOLFSSL_NO_MALLOC
 ```
 
+In addition there are two build configurations. `--enable-staticmemory=small` which is a
+smaller version that has smaller struct sizes and less supporting API's available. The other build
+configuration is `--enable-staticmemory=debug` that enables the ability to set a callback function. This is
+useful in cases where printf() is not available for determining what is being allocated and what
+bucket sizes are being used. Here is what the example client output looks like with example
+callback:
+
+```
+./examples/client/client
+...
+...
+...
+Free'ing : 16128
+OUT BUFFER: Alloc'd 6 bytes using bucket size 16992
+Alloc'd 848 bytes using bucket size 1024
+OUT BUFFER: Alloc'd 150 bytes using bucket size 16992
+Alloc'd 13 bytes using bucket size 64
+Alloc'd 12 bytes using bucket size 64
+Alloc'd 848 bytes using bucket size 1024
+IN BUFFER: Alloc'd 40 bytes using bucket size 16992
+Alloc'd 13 bytes using bucket size 64
+Alloc'd 12 bytes using bucket size 64
+Free'ing : 1024
+Free'ing : 512
+
+...
+...
+...
+```
+
 ### Using Static Buffer Allocation
 
 This can be helpful for environments without dynamic memory support, or safety-critical applications where dynamic memory use is disallowed.
@@ -727,9 +760,10 @@ For DTLS server
 
 |API|description|
 |:---|:---|
-|`wolfSSL_CTX_load_static_memory`|Set buffer for WOLFSSL_CTX as a heap memory.
-|`wolfSSL_CTX_is_static_memory`|Returns whether "Static buffer Allocation" is used. If it is the case, gets usage report. 
-|`wolfSSL_is_static_memory`|Returns whether "Static buffer Allocation" is used. If it is the case, gets usage report. |
+|[`wolfSSL_CTX_load_static_memory`](group__Memory.md#function-wolfSSL_CTX_static_memory)| Set buffer for WOLFSSL_CTX as a heap memory. |
+|[`wolfSSL_CTX_is_static_memory`](group__Memory.md#function-wolfSSL_CTX_is_static_memory)| Returns whether "Static buffer Allocation" is used. If it is the case, gets usage report. |
+|[`wolfSSL_is_static_memory`](group__Memory.md#function-wolfSSL_is_static_memory)| Returns whether "Static buffer Allocation" is used. If it is the case, gets usage report. |
+|[`wc_LoadStaticMemory`](group__Memory.md#function-wc_LoadStaticMemory)| Used to set aside static memory for wolfCrypt use. |
 |[`wolfSSL_StaticBufferSz`](group__Memory.md#function-wolfssl_staticbuffersz)| Calculate required buffer size for "Static buffer Allocation" based on the macros defined in /wolfssl/wolfcrypt/memory.h. |