Lua: Calling functions in own module

Question

I created a module for an RTC. It looks like this:

local moduleName = ...
local M = {}
_G[moduleName] = M

---------- Local variables ---------------------
local id = 0
local address = 0x68


---------- Helper functions --------------------
local function bcdToDec(val)
    local hl=bit.rshift(val, 4)
    local hh=bit.band(val,0xf)
    local hr = string.format("%d%d", hl, hh)
  return string.format("%d%d", hl, hh)
end

local function decToBcd(val)
   local d = string.format("%d",tonumber(val / 10))
   local d1 = tonumber(d*10)
   local d2 = val - d1
   return tonumber(d*16+d2)
end

---------- Module functions --------------------
function M.Init(sda, scl)
    i2c.setup(id, sda, scl, i2c.SLOW)
end


function M.PrintTime()
    i2c.start(id)
    i2c.address(id, address, i2c.TRANSMITTER)
    i2c.write(id, 0x00)
    i2c.stop(id)
    i2c.start(id)
    i2c.address(id, address, i2c.RECEIVER)
    c=i2c.read(id, 7)
    i2c.stop(id)
    s = bcdToDec(string.byte(c,1))
    m = bcdToDec(string.byte(c,2))
    h = bcdToDec(string.byte(c,3))

    time=string.format(" %s:%s:%s", h, m, s)
    print(time);
end

function M.PrintDate()
    i2c.start(id)
    i2c.address(id, address, i2c.TRANSMITTER)
    i2c.write(id, 0x00)
    i2c.stop(id)
    i2c.start(id)
    i2c.address(id, address, i2c.RECEIVER)
    c=i2c.read(id, 7)
    i2c.stop(id)
    s = bcdToDec(string.byte(c,1))
    m = bcdToDec(string.byte(c,2))
    h = bcdToDec(string.byte(c,3))
    wkd = bcdToDec(string.byte(c,4))
    day = bcdToDec(string.byte(c,5))
    month = bcdToDec(string.byte(c,6))
    year = bcdToDec(string.byte(c,7))

    time=string.format(" %s.%s.%s", day, month, year)
    print(time);
end

return M

I saved this file as "ds3231_m.lua". Calling functions from another file works like this:

m = require 'ds3231_m'
m.Init(2,1)   --sda, scl = 2, 1
m.PrintTime()
--m.PrintDate()
package.loaded.ds3231_m = Nil

as well as

m = require 'ds3231_m'
m.Init(2,1)   --sda, scl = 2, 1
--m.PrintTime()
m.PrintDate()
package.loaded.ds3231_m = Nil

But when I try calling both functions:

m = require 'ds3231_m'
m.Init(2,1)   --sda, scl = 2, 1
m.PrintTime()
m.PrintDate()
package.loaded.ds3231_m = Nil

I get an error:

test.lua:4: attempt to call field 'PrintDate' (a nil value)

Can anyone tell me what is going wrong?

Thank you very much in advance!

Regards

EinsteinK · Accepted Answer · 2016-02-16 17:14:30Z

4

Inside PrintTime (and PrintDate) you're doing m = something. That does overwrite your m from m = require(...). You should use locals in those functions:

function M.PrintTime()
    i2c.start(id)
    i2c.address(id, address, i2c.TRANSMITTER)
    i2c.write(id, 0x00)
    i2c.stop(id)
    i2c.start(id)
    i2c.address(id, address, i2c.RECEIVER)
    local c=i2c.read(id, 7)
    i2c.stop(id)
    local s = bcdToDec(string.byte(c,1))
    local m = bcdToDec(string.byte(c,2))
    local h = bcdToDec(string.byte(c,3))

    local time=string.format(" %s:%s:%s", h, m, s)
    print(time);
end

That way, you won't be editing any globals. Also do the same for PrintDate.

(If you did other_name_than_m = require(...) you wouldn't have noticed, but print(m) would still print a number, the amount of minutes from something)

answered Feb 16, 2016 at 17:14

EinsteinK

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4 Comments

mfkfx1 Over a year ago

Thank you very much, sometimes the solution is so simple :)

Rochet2 Over a year ago

He could / should possibly also use local m = require 'ds3231_m'. Depends on what he needs though.

EinsteinK Over a year ago

He probably should, but it doesn't really matter here. Inside a function, for temporary variables, you should use locals. What he does in his main script is up to him. (although locals are better in most cases)

warspyking Over a year ago

@mfxfx1 If this answer helped you be sure to press the green checkmark to accept it! That helps future readers with similar problems to find answers just like you!

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