pxsi: parameter update over serial interface
============================================

Markus Zolliker (markus.zolliker@psi.ch)

helper library for micropython on RP2040 (e.g. Arduino Nano Connect or Paspberry Pico)

Code example
------------

    from pxsi import Pxsi
    
    # declare variables visibile over serial
    
    with Pxsi('MyBox'):   # idn will be: pxsi,MyBox
        pollinterval = 5.0  # important: add decimal point in case you want this to be a float
        anint = 2
        afloat = 0.0      
        astring = 'text'

    # the given variables are now available in the main namespace

    # create action functions for some of the variables

    def change_afloat(value):
        value = float(value)  # check value is compatible with float
        # write here what to do when t changes
        return value  # return the validated value

    # here follows your real code
    
    while True:
        # handle IO, wait at most 0.5 secs
        Pxsi.handle(0.5)
        # read out sensors, do control logic here
        # important: do not sleep here!


In the change_xxx function the validity of <value> has to be checked, and if any conversion
happens the converted value has to be returned. When no change function is present, the value
is converted to the type of the initial value (e.g. float, int or str)



Serial protocol
---------------

Commands:

    name         # get value of variable name
    name=value   # change value (value must be a valid JSON value)
    ["name1", ["name2", value]]     # multiple commands: query name1, change name2. must be a valid JSON array
    {"name1": null, "name2": value} # alternative form - be aware that order is not guaranteed

    The values must match the type of initial values

Special command for identification

    *IDN?

returns:

    pxsi,<idn>


For all other commands the reply is always a JSON object:

    {"name1": value1, "name2", value2}

In case of an error, the result contains an item with the key "_error_" and a JSON array as value,
listing the errors appeared.


Hints for Arduino Nano Connect
------------------------------

For a soft reset send '\x03\x04' (Ctrl-C Ctrl-D).
The reply will be quite some text, with the last line:

    pxsi:<idn>