Re: [Paparazzi-devel] Cannon Launch Detection

[Pascal Brisset]

Hi David,

the modules mechanism should (almost) provide the features you require. 
You will have to write:
- a module description, a file in conf/modules/ : In your case, it will 
contain only a call to your init function, a call to your periodic task 
and the declaration of .c and .h files:

<!DOCTYPE module SYSTEM "module.dtd">
<module name="cld">
 <header>
   <file name="cld.h"/>
 </header>
 <init fun="cld_init()"/>
 <periodic fun="cld_check()" period="1./60" autorun="TRUE"/>
 <makefile>
   <file name="cld.c"/>
   <flag name="ADC_CLD" "ADC_7"/>
 </makefile>
</module>

- your .c and .h files in the sw/airborne/modules/cld/ folder:

---8<--- .h ---------
...
#include "std.h"
bool cld_launch_detected;
...

---8<--- .c ---------
#include "cld.h"
void cld_init(void) {
 ... initialisation code for your adc ...
 cld_launch_detected = false;
}
void cld_check(void) {
 if (... check condition...) {
    cld_launch_detected = false;
    cld_cld_status = MODULES_STOP; // stop calling me
}


- your flight plan, for example using an exception in the Holding Point 
block (in basic.xml):

   <block name="Holding point">
     <exception cond="cld_launch_detected"  deroute="Takeoff"/>
    ...
   </block>

- and finally in your airframe file:

 <modules>
   <load name="cld.xml"/>
 </modules>
...
# in the makefile section:
  ap.CFLAGS += -DUSE_MODULES


In the current implementation, 60Hz is the maximum frequency for a 
periodic task in a module. If you really need more ... let us know :-)

Hope this is enough

And feel free to update the wiki :-)

--Pascal


David Bryant wrote:
> Hi,
>
> I'm attempting to extend paparazzi to detect rapid acceleration launch 
> from a cannon. The cannon is activated by a separate system. The 
> aircraft is accelerated at approximately 24 g-force along a 3 metre 
> barrel length.
>
> I need to detect the launch within paparazzi immediately and am 
> investigating an approach based on sampling the output from a ADXL321 
> accelerometer on an ADC paparazzi input.
>
> I was hoping to be able to create a function that was periodically 
> invoked at say 200Hz and polled the accelerometer ADC input. The 
> routine would process the data until some criteria had been met that 
> indicated a launch. On detecting a launch the routine would do 
> something (invoke a function?) that would allow cause flightplan to 
> progress to the next stage. After this the routine would no longer 
> need to be called.
>
> I am currently going down the path of using the conf/modules mechanism 
> to define my function and its periodicity, and writing the function.
>
> Could someone please provide some general advice and any tips in 
> regard to my approach or an alternative approach? I am having trouble 
> finding any precedence or examples of this kind of thing. Can you draw 
> my attention to a example that I should be looking at?
>
> Thanks,
> Dave
>
>
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