add jsmn (Jasmine) JSON parser

[peterbarker]

No description provided.

[khancyr]

what is the advantage against picojson we are already using ?

[khancyr]

https://github.com/zserge/jsmn

https://github.com/kazuho/picojson

jsmm have no dynamic allocation

[peterbarker]

jsmm have no dynamic allocation

Yep. No standard library either. Really wanted json parsing on sitl-on-hardware, but had to cut it out.

[peterbarker]

I've done some more playing with this and this PR now replaced picojson with jasmine.

Cost of just having the jsmn in-play is 1424 bytes (i.e. create the parser and call it on a 1-byte string).

To actually walk through the tokens afterwards for Callisto.json to set parameters (in the same way that picojson did) costs an additional 1600 bytes.

[tridge]

we need comments, and need xplane working

[peterbarker]

we need comments, and need xplane working

So you are happy with the way this is turning out and I should pursue it, then? That's what this most recent push was in aid of - to make sure people didn't immediately throw up when they saw it.

I believe jasmine might be able to be run as a progressive parser, too - I haven't tried that, but it does have this:

  /* The string is not a full JSON packet, more bytes expected */
  JSMN_ERROR_PART = -3

... that would be rather awesome if it worked.

[peterbarker]

Works for making a CubeOrange-SimOnHardware behave like a Callisto:

I've run this through Valgrind and fixed the one false-positive.

I've made sure that XPlane dref extraction works:

... and of course, Callisto still loads in SITL.

[peterbarker]

Flash cost for CubeOrange-SimOnHW is 3kB (+ whatever JSON you want in ROMFS e.g. 1kB for Callisto.json)

--- a/libraries/AP_HAL_ChibiOS/hwdef/CubeOrange-SimOnHardWare/hwdef.dat
+++ b/libraries/AP_HAL_ChibiOS/hwdef/CubeOrange-SimOnHardWare/hwdef.dat
@@ -6,4 +6,7 @@ include ../include/SimOnHW.inc
 # short board name override (23 chars)
 define CHIBIOS_SHORT_BOARD_NAME "CubeOrangeSimOnHardWare"
 
+ROMFS models/Callisto.json Tools/autotest/models/Callisto.json
+define AP_JSONPARSER_ENABLED 1
+

./Tools/scripts/sitl-on-hardware/sitl-on-hw.py --frame octa-quad:@ROMFS/models/Callisto.json --simclass MultiCopter --vehicle copter --board CubeOrange-SimOnHardware --upload

[tridge]

failed on libraries/SITL/examples/XPlane/xplane_alia.json

[peterbarker]

failed on libraries/SITL/examples/XPlane/xplane_alia.json

Fixed - it was just the maximum number of tokens we support in a file.

[peterbarker]

@Ryanf55 I've changed this to use strtol etc

[peterbarker]

Fixed XPlane.

[peterbarker]

Going with tridge's picojson changes instead.