AFP resource consumption on micro-controllers

Reducing resource consumption

Famouso and AFP provide several possibilities to reduce the resource consumption which is important for resource constrained embedded systems like micro-controllers.

Many proposals assume that you know how to configure AFP. See How to configure AFP and Changing AFP configuration used in the Abstract Network Layer on this topic.

Choose the most simple sufficient configuration! Supporting less features results in less code and less RAM usage.
- The configuration creating the least overhead is famouso::mw::afp::Disable which can be used to disable the AFP fragmentation and/or AFP defragmentation support completely.
- The most simple configuration is famouso::mw::afp::DefaultConfig. Note that you can only use it if there are neither duplicates nor reordering and multiple events cannot arise concurrently.
- If you only subscribe for one subject, you can set multiple_subjects = false even in the Abstract Network Layer. This reduces overhead significantly if event_seq = false. Be aware of the fact that concurrent reassembly of events from multiple subjects will result in undefined behaviour.
```
 // famouso layer stack configuration
typedef famouso::mw::nl::CANNL<can, ccpClient, etagClient> nl;
struct afp_cfg : nl::AFP_Config {
    enum {
        multiple_subjects = false
    };
};
typedef famouso::mw::anl::AbstractNetworkLayer< nl, afp_cfg, afp_cfg > anl; 
```
If you do not need to support events longer than 255 bytes, you can instruct AFP to use smaller data types with the following AFP config line:
```
 typedef afp::MinimalSizeProp SizeProperties; 
```
Adjust the values of the config options:
- concurrent_events (if event_seq or multiple_subjects set)
- old_event_ids (if event_seq set)
- max_fragments (if duplicates set)
Define a custom Allocator policy. You can reduce the size of the memory pool to save RAM or a different special allocator. E.g. if multiple_subjects = event_seq = duplicates = reordering = FEC = false you can use object::OneBlockAllocator.
You may disable overflow_error_checking.

Reducing resource consumption in general for release versions:

Define the preprocessor symbol LOGGING_DISABLE when invoking the compiler to disable logging globally.
Define the preprocessor symbol NDEBUG to disable all run-time assertions.

The following table illustrates the Flash and RAM resource consumption of some simple AFP configurations on an AVR at90can128 micro-controller build with avr-g++ 4.4.3. The values include the famouso middleware and a CAN driver. The source is located in the directory tst/approved/AFP/avr-size.

Node type	Max. event size (Bytes)	AFP	Section text (Bytes)	Section data (Bytes)	Section bss (Bytes)	Filename
publisher	8	none	2594	28	38	can-pub-no-afp
	255	ANL	3604	28	38	can-pub-anl
	255	Application Layer	3060	28	38	can-pub-al
subscriber	8	none	2640	28	38	can-sub-no-afp
	255	ANL	4092	28	347	can-sub-anl
	255	Application Layer	3386	28	301	can-sub-al

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AFP resource consumption on micro-controllers

Reducing resource consumption

Resource consumption examples