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3.2
Software design
35
a GPI/O pin is not needed anymore, it can be unallocated
with the function gpio free(portpin).
To make use of the metrology engine of the EM773,
the EM773 SDK contains a module that controls
this engine.
Before using the metrology engine, it
first needs to be configured. This is done by calling
metrology init(AHBClkFrequency, Fmains),
which needs the clock frequency (AHBClkFrequency)
and the frequency of the mains (Fmains). If Fmains is
set to EM AUTO, the mains frequency is detected automatically and returned as the result of the initialization
function. The second step of the configuration is to call
metrology set ranges(ranges). How the parameter
ranges is used, is extensively explained in the user
manual of the EM773. Before any metering data becomes
available, the metrology engine has to be started. This is
done with metrology start(). To stop the metering,
metrology stop() can be called. To obtain metering
data from the metrology engine the function metrology read data(metrology result) has to be used. This
function writes the metering data into the variable pointed
at by the pointer parameter metrology result, if metering data is available. The function returns whether reading
metering data was successful or not. This concludes the
part, in which I describe the modules I used from the
EM773 SDK. In the next part I will talk about the modules
I have added myself.
To refresh the data from the metrology engine in a certain
time interval and to make it available, I added the module
metering to the package METROLOGY. The functionality
of the refreshing is based on a timer. The used timer is
configured to count milliseconds. An interrupt is fired
and the counter resets, when the counter reaches the value
of the define METERING INTERRUPT FREQUENCY. The
corresponding ISR reads out the data using the function
metrology read data(&metering result).
The metering data is then available in the
The
function
variable
metering result.
Initialise Metering() handles the configuration
of the complete metering system. This includes calling the
functions metrology init(AHBClkFrequency,
the module
metrology can be
used to control the
metrology engine
init functions must
first be called before
use
after starting the
metrology engine, its
data can be read
with a read method
I wrote a module that
makes sure update
metering data is
available
the init function of
this module, takes
care of the complete
initialization of the
metrology engine