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Forum Index : Microcontroller and PC projects : Micromite eXtreme 5.04.17: JSON parsing

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Joined: 11/12/2012
Location: United Kingdom
Posts: 6619
Posted: 01:25pm 08 Jun 2018
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Please find attached MMX version 5.04.17 for the 100/144pin chip


and for the 64-pin chip


Updated manual


This release includes the ability to parse JSON strings stored in a longstring. The attached program shows how I use this to read the weather from openweathermap.org using a ESP8266 with standard "AT" firmware. Substitute myAPIKEY, mySSID and myPASSWORD with your own values.

The release also includes a new sub command LONGSTRING PRINT [#n,] src%(). This prints the longstring stored in src%() to either a file, a serial port, or the console.

option explicit
option default none
Dim MYID$="2638878"
Dim report$="weather"
dim b$= "GET /data/2.5/"+report$+"?id="+MYID$+"&APPID="+APIKEY$
Dim m%(8000)
b$=b$+" HTTP/1.0"+Chr$(13)+Chr$(10)+Chr$(13)+Chr$(10)

open "com1:115200,8192" as #1
LongString clear m%()
print #1,"AT+CWMODE_CUR=1"+chr$(13)+chr$(10);
if NOT OKwait(4000) then errorexit("AT+CWMODE_CUR=1")
print #1,"AT+CWJAP_CUR="+chr$(34)+"mySSID"+chr$(34)+","+chr$(34)+"myPASSWORD"+chr$(34)+chr$(13)+chr$(10);
if NOT OKwait(10000) then errorexit("AT+CWJAP_CUR=")
print #1,"AT+CIPSTART="+chr$(34)+"TCP"+chr$(34)+","+chr$(34)+"api.openweathermap.org"+chr$(34)+",80"+chr$(13)+chr$(10);
if NOT OKwait(10000) then errorexit("AT+CIPSTART=")
print #1,"AT+CIPMODE=1"+chr$(13)+chr$(10);
if NOT OKwait(4000) then errorexit("AT+CIPMODE=1")
print #1,"AT+CIPSEND"+chr$(13)+chr$(10);
if NOT OKwait(4000) then errorexit("AT+CIPSEND")
print #1,b$;
Print "Weather for "+json$(m%(),"name")
Print "Temperature is ",val(json$(m%(),"main.temp"))-273
Print "Pressure is ",json$(m%(),"main.pressure")
Print json$(m%(),"weather[0].description")
print #1,"+++";
pause 1000
print #1,"AT+CIPMODE=0"+chr$(13)+chr$(10);
if NOT OKwait(4000) then errorexit("AT+CIPMODE=0")
print #1,"AT+CIPCLOSE"+chr$(13)+chr$(10);
if NOT OKwait(4000) then errorexit("AT+CIPCLOSE")

function OKwait(timeout as integer) as integer
loop until input$(1,1)="O" or timer>=timeout
loop until input$(1,1)="K" or timer>=timeout
if timer>=timeout then OKwait=0
end function

sub errorexit(calling as string)
print "AT call timeout from - ",calling
print #1,"AT+CIPCLOSE"+chr$(13)+chr$(10)
end sub

sub getinput(waitpause as integer)
local a$
local j%,i%=-1
If a$<>"" Then
LongString append m%(),a$
' print a$;
if a$="{" then
if i%=-1 then
if a$="}" then i%=i%-1
loop while timer<=waitpause and i%<>0
LongString trim m%(),LInStr(m%(),"{")-1
print ""
end sub
Edited by matherp 2018-06-09
Regular Member

Joined: 26/06/2016
Location: Australia
Posts: 51
Posted: 01:52am 19 Jan 2019
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Have been using JSON parsing on openweathermap on weather and just trying it out on the 5 day forecast. MMX64 v5.0501
I am running this command for testing, 'Print JSON$(m%(),"list[0].main.temp")', I get 'Error: Not enough memory'. Afterwards, running 'files' at the command line shows the same. Need to do a 'cpu restart' to clear. Using m%(8000), did try higher values.

The forecast JSON data has 39 part-day entries (list[x]) which may be the issue. I manually removed all but one entry and it ran ok. If I remove the part-day data after entry 18, it works ok. Doing the same after day 20 and the issue returns.

What's the limit for this type of parse?


Joined: 18/11/2011
Location: United Kingdom
Posts: 2922
Posted: 08:11am 19 Jan 2019
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m%(8000) sounds like nearly 64K RAM (*) just for that - is that available as well as all the other space needed?

(*) I think they're 64-bit, not 32-bit when it would be 32K

JohnEdited by JohnS 2019-01-20

Joined: 11/12/2012
Location: United Kingdom
Posts: 6619
Posted: 08:40am 19 Jan 2019
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  Quote  What's the limit for this type of parse?

It isn't possible to say. The parser allocates memory (malloc()) as it walks through the json string and the longer and more nested the string the more memory it will need. The array used should be the smallest possible that holds the string to leave as much other memory free as possible for the parser to allocate as it processes.

One specific technical issue in MMBasic is that the smallest amount of memory that can be "malloc"ed is 256 bytes. In general this works well but for this parser it is very wasteful - nothing I can do about this as it is deeply embedded in MMBasic.
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