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JSON Details
(last updated 1/23/13 - ash)
This page is really a continuation of this page
NOTE: This page describes JSON operations in release 0.95 and later. Currently this code is only in the edge and dev branches. If you want to try it we recommend using the edge branch as it's more stable than dev.
#JSON Details ##JSON Mode Protocol
Commands in JSON mode are sent as JSON messages. Some examples:
{"x":""}<lf> get the X resource
{"xvm":12000}<lf> set the X maximum velocity to 12000 mm/min (assuming the system is in G21 mode)
{"gc":"g0 x100"}<lf> execute the Gcode block "G0 X100"
Responses are wrapped in a response body and include a footer. Responses can be up to 256 characters long but generally are much shorter.
The entire JSON response object is terminated by CR, LF or CR/LF depending on the board configuration settings ($ec, $el)
Responses to the above examples are:
{"r":{"x":{"am":1,"vm":16000.000,"fr":16000.000,"tm":220.000,"jm":5000000000.000,"jd":0.010,"sn":3,"sx":2,"sv":3000.000,"lv":100.000,"lb":20.000,"zb":3.000}},"f":[1,0,9,9580]}
{"r":{"xvm":12000.000},"f":[1,0,14,3009]}
{"r":{"gc":"g0x100"},"f":[1,0,17,9360]}
where "f":[1,0,255,1234]
is "f":[<protocol_version>, <status_code>, <input_available>, <checksum>]
The footer contains a 4 element array:
Element | Notes
-------|-------------------------
array_ID/version | Initially set to 1. This number identifies the array and version for the parser. It will be incremented if protocol changes are made that would affect hosts/clients
status_code | 0 is OK. All others are exceptions. See [tinyg.h](https://github.com/synthetos/TinyG/blob/edge/firmware/tinyg/tinyg.h) for details
RX_received | Indicates how many characters were removed from the serial RX buffer to process this command. This allows the host to keep a running total of the bytes available in the TinyG RX buffer. The RX buffer typically starts with 254 bytes free. The terminating `<LF>` counts as a byte.
checksum | A 4 digit checksum for the line. The checksum is generated for the JSON line up to but not including the comma preceding the checksum itself. I.e, the comma is where the nul termination would exist. The checksum is computed as a [Java hashcode](http://en.wikipedia.org/wiki/Java_hashCode(\)) from which a modulo 9999 is taken to limit the length to no more than 4 characters. See compute_checksum() in util.c for C code.
Character echo ($ee) is always an option; it's just not a good one for JSON. In JSON mode it should be turned off ( $ee=0, or {"ee":0} ). It's a matter of preference for text mode.
JSON verbosity ($jv) sets the level of verbosity in JSON responses. It is set by {"jv":N} where N is one of:
- 0 = SILENT - no response
- 1 = FOOTER_ONLY - no body data is returned, only footer data
- 2 = OMIT_GCODE_BODY - body returned for configs; omitted for Gcode commands
- 3 = GCODE_LINENUM_ONLY - body returned for configs; Gcode returns line number as 'n', otherwise body is omitted
- 4 = GCODE_MESSAGES - body returned for configs; Gcode returns line numbers and messages only
- 5 = VERBOSE - body returned for configs and Gcode - Gcode comments removed
Generally levels 2, 3 or 4 are recommended. Levels 4 and 5 will return Gcode comment messages of the form (msgSome text you want to show to the operator)
###Reading Configuration Parameters (GET) To get a parameter pass an object with a null value. The value is returned in the response. Some examples of valid requests and responses are provided below.
Request | Response | Description
------|---------|---------|--------------
xfr | $xfr | {"xfr":""} | X axis maximum feed rate
cjm | $cjm | {"cjm":""} | C axis maximum jerk
1mi | $1mi | {"1mi":""} | Motor 1 microstep setting
home | $home | {"home":""} | Homing state group - returns system state and each axis
Request | Response | Description
---------|--------------|-------------
{"xvm":""} | {"r":{"xvm":16000},"f":[1,0,11,1301]}<nl>| get X axis maximum velocity
{"x":{"vm":""}} | {"r":{"x":{"vm":16000}},"f":[1,0,16,2128]}<nl>| alternate form to get X axis maximum velocity
{"x":""} | {"r":{"x":{"am":1,"vm":16000.000,"fr":16000.000,.... | get entire X axis group
###Setting Configuration Parameters (PUT)
To set a parameter pass an object with the value to be set. The value taken is returned in the response. The response value may be different than the requested valued in some cases. For example, an attempt to set a status report interval less than the minimum will return the minimum interval. Trying to set a read-only value will return that value; for example, firmware version. In some other cases a value of 'false' will be returned. The following are examples of valid set commands.
Request | Response | Description
---------|--------------|-------------
{"xvm":15000} | {"r":{"xvm":15000},"f":[1,0,14,9253]}<nl>| set X axis maximum velocity to 15000
{"x":{"vm":15000}} | {"r":{"x":{"vm":15000},"f":[1,0,19,2131]}}<nl>| alternate form to set X axis maximum velocity to 15000
{"si":250} | {"r":{"si":250.000},"f":[1,0,19,2131]}<nl>| Set status minimum interval to 250 ms.
{"si":10} | {"r":{"si":50.000},"f":[1,0,19,2131]}<nl>| Attempt to set status interval to 10 ms, but minimum was 50, so that's what stuck
{"fv":2.0} | {"r":{"fv":0.950},"f":[1,0,19,2131]}<nl> | Whilst you may want a version 2.0 to magically appear the firmware remains at version 0.95 :(
'bd' '''{returned body object}''' This is a JSON object that is one of:
*a configuration parameter response, e.g. {"xvm":600.000}
*a group response, e.g. {"x":{"am":1,"vm":600.000,"fr":600.000,"tm":475.000,"jm":20000000.000,"jd":0.050,"sm":1,"sv":-500.000,"lv":100.000,"lb":2.000,"zb":1.000}}
*a Gcode response, e.g.{"gc":"G0X90"} (Note: this is a change from 0.93/0.94 as the gcode object is now just the command line, no status or message)
*a status report, e.g. {"sr":{"line":3,"posx":90.000,"posy":0.000,"posz":50.000,"posa":0.000,"feed":0.000,"vel":0.000,"unit":1,"coor":1,"dist":0,"frmo":0,"momo":0,"stat":2}}
*a message, e.g. {"msg":"Some text that should be displayed to the user"} (note, a mesage field may also follow any of the above in the response body)
'''"sc" Status Code'''
A status code of '0' is OK. All others are errors. Check tinyg.h for the most up-to-date list, and see controller.c for corresponding end-user status messages.
// OS, communications and low-level status (must align with XIO_xxxx codes in xio.h) #define TG_OK 0 // function completed OK #define TG_ERROR 1 // generic error return (EPERM) #define TG_EAGAIN 2 // function would block here (call again) #define TG_NOOP 3 // function had no-operation #define TG_COMPLETE 4 // operation is complete #define TG_TERMINATE 5 // operation terminated (gracefully) #define TG_ABORT 6 // operaation aborted #define TG_EOL 7 // function returned end-of-line #define TG_EOF 8 // function returned end-of-file #define TG_FILE_NOT_OPEN 9 #define TG_FILE_SIZE_EXCEEDED 10 #define TG_NO_SUCH_DEVICE 11 #define TG_BUFFER_EMPTY 12 #define TG_BUFFER_FULL_FATAL 13 #define TG_BUFFER_FULL_NON_FATAL 14 // NOTE: XIO codes align to here // Internal errors and startup messages #define TG_INTERNAL_ERROR 20 // unrecoverable internal error #define TG_INTERNAL_RANGE_ERROR 21 // number range other than by user input #define TG_FLOATING_POINT_ERROR 22 // number conversion error #define TG_DIVIDE_BY_ZERO 23 // Input errors (400's, if you will) #define TG_UNRECOGNIZED_COMMAND 40 // parser didn't recognize the command #define TG_EXPECTED_COMMAND_LETTER 41 // malformed line to parser #define TG_BAD_NUMBER_FORMAT 42 // number format error #define TG_INPUT_EXCEEDS_MAX_LENGTH 43 // input string is too long #define TG_INPUT_VALUE_TOO_SMALL 44 // input error: value is under minimum #define TG_INPUT_VALUE_TOO_LARGE 45 // input error: value is over maximum #define TG_INPUT_VALUE_RANGE_ERROR 46 // input error: value is out-of-range #define TG_INPUT_VALUE_UNSUPPORTED 47 // input error: value is not supported #define TG_JSON_SYNTAX_ERROR 48 // JSON string is not well formed #define TG_JSON_TOO_MANY_PAIRS 49 // JSON string or has too many JSON pairs // Gcode and machining errors #define TG_ZERO_LENGTH_MOVE 60 // move is zero length #define TG_GCODE_BLOCK_SKIPPED 61 // block is too short - was skipped #define TG_GCODE_INPUT_ERROR 62 // general error for gcode input #define TG_GCODE_FEEDRATE_ERROR 63 // move has no feedrate #define TG_GCODE_AXIS_WORD_MISSING 64 // command requires at least one axis present #define TG_MODAL_GROUP_VIOLATION 65 // gcode modal group error #define TG_HOMING_CYCLE_FAILED 66 // homing cycle did not complete #define TG_MAX_TRAVEL_EXCEEDED 67 #define TG_MAX_SPINDLE_SPEED_EXCEEDED 68 #define TG_ARC_SPECIFICATION_ERROR 69 // arc specification error
At some point we may want to distinguish between fatal and non fatal errors.
'''"sm" Status Message'''
Status messages are end-user text associated with each error code (see controller.c). Not all commands are required to return messages (for example, status reports may not). Parsers should work to the status codes, NOT the messages, as messages may change or be omitted.
Note: these are distinct from application messages that may be returned from Gcode MSG fields, or from system startup operations.
'''"buf"''' RX buffer bytes available
This value is how many bytes are available in the serial input buffer (RX buffer). An empty buffer has 254 bytes. As the RX buffer fill up this number goes down until a command is read out of the buffer. Then it goes back up by the length of the line read. This value is used for synchronization with host drivers.
'''"ln"''' Last line number processed
This is the line number of the line that was most recently pulled out of the buffer, or the "gcode model" line number. This number will be populate with the N word sent in the Gcode block - e.g. N300. If no N word is populated the line number will advance by 1 for each new line sent in. Since Gcode does not require every line to have a number (or any!), this can lead to some odd behaviors. Say you set N300, then followed with 20 lines without N words. Then sent N310. The line number will advance to 320, then reset to 310. You are your own master. Note that the line number reported in "ln" (the model line number) is different than the runtime line number reported as "line" in a status report. "Line" is the line currently being executed by the steppers. The model line number may lag the runtime line number by as many as 24 moves, depending on how deep the move planner is.
Be aware that BX buffer space is being under-reported in most cases. The controller module is continuously pulling characters off the RX buffer into a separate input buffer (string). When the input string has a full command ready for processing it's another 100 microseconds or so before the model line number is updated and available for return (e.g. on a status report or some other asynchronous response). Then typically it will be another 3000 microseconds (+ or -) before the command is actually processed and the response to the command is returned with the new model line number. This under-reporting should not cause problems for command synchronization with the host, but it's good to know it's happening.
'''"cks"''' Checksum
The checksum is always the last item on the line. The checksum is the decimal Java hashCode of the string starting with the opening curly (in front the "r") to the "cks" name. For example:
for this string ---------> {"r.:{"bd":{"gc":"g0x100"},"sc":0,"sm":"OK","cks":"3756753382"}}
take checksum of --> {"r.:{"bd":{"gc":"g0x100"},"sc":0,"sm":"OK","cks"
Do not include a CR or line terminator in the checksum.
See [http://en.wikipedia.org/wiki/Java_hashCode() en.wikipedia.org/wiki/Java_hashCode()] or the algorithm
== Get and Set Configuration Parameters ==
== Gcode in JSON ==
In JSON mode Gcode blocks may be provided either as native gcode text or wrapped in JSON as a "gc" object. In either case responses will be returned in JSON format. A JSON wrapper may only contain a single gcode block.
Gcode requests
{"gc":"g0 x100"} wrapped input
g0 x100 unwrapped input
{"gc":"g0 x100 (Initial move)"} wrapped input with a Gcode comment (see note)
{"gc":"m0 (MSGChange tool and hit Cycle Start when done)"} stop with a message
Gcode responses
{"r":{bd:{"gc":"G0X100"},"st":0,"sm":"OK","cks":123456789}}
{"r":{bd:{"gc":"G0X100 (Initial move)"},"st":0,"sm":"OK","cks":123456789}}
{"r":{bd:{"gc":"M0","msg":"Change tool and hit Cycle Start when done"},"st":0,"sm":"OK","cks":123456789}}
The first response is pretty normal. The second has a comment in it. The third is what would happen if a MSG were communicated in the Gcode comment.
Note: We are still undecided on how to handle comments in the Gcode. These could be returned in the gcode response as illustrataed, but currently they are stripped.
Note: We are still debating if line numbers should be returned as a separate JSON element, e.g. "gc":"G0X100","line":2245. See issue #23 on the TinyG github
== Status Reports in JSON ==
Status reports are parent/child objects with a "sr" parent and one or more child NV pairs, as in the example below.
{"sr": {"line":1245, "xpos":23.4352, "ypos":-9.4386, "zpos":0.125, "vel":600, "unit":"mm", "stat":"run"}}
The following use-cases are supported:
*SET status report fields. The elements to be included in a status reports may be specified by setting values to 'true'. The elements will be returned on subsequent SR requests in the order they were provided in the SET command. (I know, dictionaries are supposed to be unordered, but the firmware will record and return back the attributes in the order listed). There is no incremental setting of elements - all attributes are reset and must be specified in a single SET command. For example, the string below could be used to set up the status report in the example above, and eliminate any previously recorded settings. Note that the 'true' term is not in quotes - it is actually the JSON value for true, not a string that says "true". Examples:
{"sr":{"line":true,"xpos":true, "ypos":true,"zpos":true, "vel":true, "unit":true, "stat":true}}
{"status_report":{"line":true,"xpos":true, "ypos":true,"zpos":true, "vel":true, "unit":true, "stat":true}} - this is the same as the above but using the friendly name
*GET an on-demand status report - this will return a single status report. All forms below are equivalent. The first two use friendly names, the last two use mnemonic tokens.
{"status_report":""}
{"status_report":null} the 'null' value is used instead of "" in this case. Either are accepted.
{"sr":""}
{"sr":null}
*Request an ad-hoc report. An ad-hoc query for one or more name/value pairs can be performed. This is technically not a "status report", but it's useful. This is really just multiple GET requests in a single JSON object.
{"line":"","xpos":"","ypos":"","zpos":"","vel":"","unit":"","stat":""} request GETS for the listed values
{"line":1245, "xpos":23.4352, "ypos":-9.4386, "zpos":0.125, "vel":600, "unit":"mm", "stat":"run"} returns the NV pairs. Note the absence of the SR parent object.
*Automatic status reports. Status reports may also be automatically generated by setting the status report interval to a non-zero value. Reports will be generated during movement every N milliseconds, and at the end of each Gcode bloack that causes a movement, and when the machine has stopped (i.e. at the end of the final move in the buffer).
{"status_interval":0} disable automatic status reports
{"status_interval":200} request status reports every 200 ms during movement
{"si":200} same as above
A status report may contain one or more of the following attributes. The [token] and the friendly name are listed. Values are returned as numbers. (note: A CSV string is returned when in text mode)
[vel] velocity - actual velocity - may be different than programmed feed rate [line] line_number - either the Gcode line number (N word), or the auto-generated line count if N's are no present [feed] feed_rate - gcode programmed feed rate (F word) [stat] machine_state - 0=reset, 2=stop, 3=end, 4=run, 5=hold, 6=homing [unit] units_mode - 0=inch, 1=mm [coor] coordinate_system - 0=g53, 1=g54, 2=g55, 3=g56, 4=g57, 5=g58, 6=g59 [momo] motion_mode - 0=traverse, 1=straight feed, 2=cw arc, 3=ccw arc [plan] plane_select - 0=XY plane, 1=XZ plane, 2=YZ plane [path] path_control_mode - 0=exact stop, 1=exact path, 2=continuous [dist] distance_mode - 0=absolute distance, 1=incremental distance [frmo] feed_rate_mode - 0=units-per-minute-mode, 1=inverse-time-mode [gc] gcode_block - gcode block currently being run [mpox] mpox (x absolute position) - X machine position in absolute coordinate system in prevailing units (mm or inch) [mpoy] mpoy (y absolute position) [mpoz] mpoz (z_absolute position) [mpoa] mpoa (a absolute position) [mpob] mpob (b absolute position) [mpoc] mpoc (c absolute position) [posx] posx (x position) - X work position in prevailing units (mm or inch) [posy] posy (y position) [posz] posz (z position) [posa] posa (a position) [posb] posb (b position) [posc] posc (c position) [g92x] g92x - G92 origin offset for X axis [g92y] g92y [g92z] g92z [g29a] g92a [g92b] g92b [g92c] g92c Additionally, any valid token may be listed in a status report. For example, "g54x" will return the X offset in the G54 coordiante system (coordinate system #1). "fv" would return the firmware version.
== Group Resources ==
"Groups" are related parameters or settings. The following groups are defined:
*Axis groups [x,y,z,a,b,c] - contains all per-axis configuration settings such as maximum velocity and axis travel *Motor groups [1,2,3,4] - contains all per-motor configuration settings such as steps per revolution or microsteps *Coordinate system offset groups [g54,g55,g56,g57,g58,g59] - contains offsets for xyzabc axes. *System group - special group with system and global parameters
See TinyG:Configuring] for details about the settings available in groups.
Groups are treated specially in JSON. The group prefix is "pulled out" and used as the parent object ID for the child NV pairs. For example, here is a standard (non-group) JSON line with all motor parameters for motor #2:
{"2ma":1,"2sa":1.8,"2tr":1.275,"2mi":2,"2po":0,"2pm":1}
where:
[2ma] m2_map_to_axis
[2sa] m2_step_angle
[2tr] m2_travel_per_revolution
[2mi] m2_microsteps
[2po] m2_polarity
[2pm] m2_power_management
Here is the same set of parameters represented as a group resource:
{"2":{"ma":1,"sa":1.8,"tr":1.275,"mi":2,"po":0,"pm":1}}
These are handled identically by the JSON parser. Either line above would have set all the values in the list. If null's had been provided all values would have been returned.
A group resource can also be retrieved by its parent name alone:
{"2":""} returns:
{"2":{"ma":1,"sa":1.8,"tr":1.275,"mi":2,"po":0,"pm":1}}
Another advantage of the group form is that all motors will serialize / deserialize in host code to well-defined objects, making for convenient host coding. Essentially a resource can be instantiated in the host program, serialized to JSON, then sent to the the firmware to set all values in the resource. The same is true in reverse. You can think of r attributes as being in an implicit dotted notation: e.g. x.fr, 1.sa, or g55.x
'''''Here is an short Python Script that illustrates how easy it is to get data back from TinyG in a programatic way.'''''
#!/usr/bin/python
import json
motor_settings = '{"2":{"ma":1,"sa":1.8,"tr":1.275,"mi":2,"po":0,"pm":1}}'
#motor_settings is an example response you would get from TG if you issued a {"2":""}\n command
motors=json.loads(motor_settings) #load the response into a python dict.
#Break out individual values into vars.
microSteps, travelRevs, stepAngle, polarity, powerManagement = (motors["2"]["ma"], p["2"]["tr"], p["2"]["sa"], p["2"]["po"], p["2"]["pm"])
Some other examples of group resoruces:
{"x":{"am":1,"fr":1000,"vm":1000,"tm":100,"jm":100000000,"jd":0.05,"sm":1,"sv":1000,"lv":100,"zo":4,"abs":"","pos":""}}
{"y":{"am":1,"fr":1000,"vm":1000,"tm":100,"jm":100000000,"jd":0.05,"sm":1,"sv":1000,"lv":100,"zo":4,"abs":"","pos":""}}
{"z":{"am":1,"fr":1000,"vm":1000,"tm":100,"jm":100000000,"jd":0.05,"sm":1,"sv":1000,"lv":100,"zo":4,"abs":"","pos":""}}
{"g54":{"x":0.000,""y":0.000,"z":0.000,"a",0.000,"b":0.000,"c":0.000}}
{"g55":{"x":50.000,""y":50.000,"z":-10.000,"a",0.000,"b":0.000,"c":0.000}}
=== System Group ===
The System Group is a special case that handles system and global values that don't have have a common prefix. The system group is identified by "sys". Here are the members of the system group listed as a plain list and as a group resource.
{"fv":"","fb":"","si":"","gpl":"","gun":"","gco":"","gpa":"","gdi":"",ea":"","ja":"","ml":"","ma":"","mt":"","ic":"","il":"","ec":"","ee":"","ex":""} - as a plain list
{"sys":{"fv":"","fb":"","si":"","gpl":"","gun":"","gco":"","gpa":"","gdi":"",ea":"","ja":"","ml":"","ma":"","mt":"","ic":"","il":"","ec":"","ee":"","ex":""}} - as a system group
{"sys":""} - returns all values in the system group
[fv] firmware_version
[fb] firmware_build
[si] status_interval
[gpl] gcode_select_plane - power-on and reset default, not equivalent to G17, G18, G19
[gun] gcode_units_mode - power-on and reset default, not equivalent to G20, G21
[gco] gcode_coord_system - power-on and reset default, not equivalent to G54 - G59
[gpa] gcode_path_control - power-on and reset default, not equivalent to G61, G61.1, G64
[gdi] gcode_distance_mode - power-on and reset default, not equivalent to G90, G91
[ea] enable_acceleration
[ja] junction_acceleration
[ml] min_line_segment
[ma] min_arc_segment
[mt] min_segment_time
[ic] ignore_CR/LF (on RX)
[ec] enable_CR (on TX)
[ee] enable_echo
[ex] enable_xon_xoff
[ej] enable_json_mode on startup