avr: added docu

avr/devices/all/README

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+
+Functions
+
+AqHome knows these driver/module/app functions:
+- INIT: initialize the driver
+- RUN:  called on every loop
+- MSGRECEIVED: called whenever a message has been received
+- EVERY100MS:  called every 100ms (the system timer tick)
+- EVERY1S:     called every second
+- EVERY1M:     called every minute
+- EVERY1H:     called every hour
+- EVERY1D:     called every day
+
+
+Modules and Apps
+
+Modules are lowlevel drivers for specific hardware (like for the environment
+sensor SI7021).
+
+Apps on the other hand are kind of sub-programs running in parallel on the
+microprocessor. E.g. there are apps for networking, motion-activated-light, statistics
+reporting and sensor value reporting.
+
+
+Modules
+
+If your driver/module implements those functions they need to be added
+to the appropriate files:
+- include instructions to the file "modules_include.asm"
+- calls to INIT function to        "modules_init.asm"
+- calls to RUN function to         "modules_run.asm"
+- calls to MSGRECEIVED function to "modules_msg.asm"
+- calls to EVERY100MS function to  "modules_100ms.asm"
+- calls to EVERY1S function to     "modules_1s.asm"
+- calls to EVERY1M function to     "modules_1m.asm"
+- calls to EVERY1H function to     "modules_1h.asm"
+- calls to EVERY1D function to     "modules_1d.asm"
+
+Only implemented routine calls need to be added, e.g. if a driver doesn't need
+the RUN functionality it doesn't need to be implemented.
+
+
+Apps
+
+The same rules apply to apps. The only difference is the prefix of the files calls and
+include directives need to be added (using "apps_xxx.asm" instead of "modules_xxx.asm").
+
+