Lua: Calling functions in own module - lua

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

Answer 1

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)