Keeping state when awaking from sleep

[gregcope]

Hi,

When sleeping other micro controllers (e.g. ATMEL) pick up where they left off, with state mostly the same (ie pin states, memory structures, but usually not the clock - depends on mode). This makes sleeping and saving power easy.

As the pycom boards seem to restart (ie (re)run boot.py and main.py) when re-awaking from sleep what are peoples thoughts on maintaining state?

For example you can use pin.hold([hold])to fix pin state which is good.

What about variables or state? Use pycom.nvs_set(key, value)? However this can only hold 32 bit ints'.

Thoughts?

[jcaron]

@gregcope Depending on what you need to save exactly, you can also use the flash file system to save/restore data. Probably not a good idea if you save on each sleep and you wake up often, but for data that does not change too much, it should be a good option.

[gregcope]

@jcaron Good point.

[mdk22]

I had to create a library myself to save a string of streams in the nvram, along with this, the soft reset option can keep hardware states saved.

[gregcope]

@mdk22 can you share your lib?

[mdk22]

@gregcope

# Written by Mayunk Kulkarni
import binascii
from pycom import nvs_set, nvs_get

class NvsStore():
#   this class basically stores the string and topic provided in the nvram
#    given the fact that the string sizes can be variable. Using a variety of
#    functions to convert string in to int and int back to string we use this
#    class to store a topic and string in a series of nvram cells

    def __init__(self, topic, stringToStore):

        self.string = stringToStore
        self.topic = topic
        self.__Init(self.string, self.topic)

    def __Init(self, string, topic):
        # step 1: split string into a list of strings each of maximum 4 chars
        # step 2: store the topic and string in the nvram cell and use str2int
        #         to shift each list componenent into nvram
        self.strSplit(string)
        self.store(topic)

    def str2int(self, string):
        x = binascii.hexlify(string)
        x = int(x, 16)
        x = x + 0x200
        return x

    def store(self, topic):
        # store list values into nvram topic spaces
        for i in range(len(self.strlist)):
            nvs_set(topic+str(i), self.str2int(self.strlist[i]))

    def strSplit(self, string):
        # split string into 4 chars each and put it in a list
        self.strlist = []
        temp = string
        while temp != "":
            if len(temp) < 4 or len(temp) == 4:
                self.strlist.append(temp)
                break
            self.strlist.append(temp[len(temp)-4:len(temp)])
            temp = temp[:len(temp)-4]

    def intcount(self, val):
        # old function used for debugging
        y = val
        i = 0
        while int(y/10) != 0:
            y = y / 10
            i+=1
        return i


class NvsExtract():
#   This class will be used to extract and return string values back to  
#   pycom for their use in lora, wifi, LTE services. The topic keys are
#   constant hence we can find the strings yet we need to use try/except
#   to catch error for finding limit of a certain topic string

    def __init__(self, topic):
        self.topic = topic
        self.__Init(self.topic)

    def __Init(self, topic):
        self.extractInt(topic)

    def extractInt(self, topic):
        # extract integer from nvram topic and put string in self.string
        cnt = 0
        self.string = ""
        x = []
        while True:
            if nvs_get(topic+str(cnt)) == None:
                break
            else:
                x.append(self.int2str(nvs_get(topic+str(cnt))).decode("utf-8"))
                cnt += 1
        while len(x) > 0:
            self.string = self.string + x[len(x) -1]
            x = x[:len(x)-1]
        temp = self.string

    def retval(self):
        return self.string

    def int2str(self, integer):
        #convert integer obtained into character string
        integer = integer - 0x200
        integer = hex(integer)
        return binascii.unhexlify(integer[2:])

test = False
if test == True:
    NvsStore("ssid", "one")
    NvsExtract("ssid")

Here it is, let me know any suggestions or issues, I am new to this developer community.

[jcaron]

@mdk22 A few comments:

• You should probably store the length separately
• You should add a (documented) separator between the topic and the index. Otherwise you may end up with collisions when you store thing and thing1 for instance
• Not sure I figured the reason for the 0x200, but that means you can end up with an overflow

[gregcope]

@jcaron thanks

[mdk22]

@jcaron thanks, I will keep improving the library.