Re: Translating an embedded C algorithm

[Cesar Rabak <csrabak@yahoo.com.br>]

Vo, Anh (US SSA) escreveu:
> -----Original Message----- From: comp.lang.ada-bounces@ada-france.org
> [mailto:comp.lang.ada-bounces@ada-france.org] On Behalf Of Cesar
> Rabak
> 
> Vo, Anh (US SSA) escreveu:
>> -----Original Message-----
> [snipped] A suggestion for the OP:
> 
> <    MINIMUM_ADC_COUNT : constant := Integer'Last; <
> MAXIMUM_ADC_COUNT : constant := Integer'Last; <    SPACING : constant
> := 1; ..
>> MINIMUM_ADC_COUNT : constant := 220; MAXIMUM_ADC_COUNT : constant
>> := 468; SPACING : constant := 8;
> 
> The values 220 and 468 come from its Table 1 (PDF file). Also SPACING
> is described as being 8.
> 
> Thanks for pointing these values out. I did it in hurry. So, I did
> not read the PDF file in details. Today I attempted to find out where
> ReadEEPROM table or function is defined. I did not see it. In
> addition, I did ask for its definition. However, it was left out.
> Again, here it is.

You're welcome. I also did read very diagonally, probably an
implementation of mine would have errors as well ;-)

> 
> function ReadEEPROM (Temp : in Integer) return Integer is begin 
> return Temp; -- for now end ReadEEPROM;
> 
> I assume ReadEEPROM is a function. Whether it is a table or a
> function, it needs to be defined. Assume that ReadEEPROM is defined,
> here is the updated version of it. Thanks to Christoph Grein for his
> correction.
> 

Here a comment: it's the right assumption per OP description and
C code. However, I think that in an embedded system (specially for a
microcontroller) the cost of a function call just to get a value may be
not worth of. As the value of the argument seems to be a constant (all
uppercase names in C normally are macros), I think ReadEEPROM just reads
a memory (in E�PROM probably).

> ----------------------------------------------------------------------
>  --| MeasureTemperature --| --| Calculates the temperature in �C
> given the ADC count by lookup --| table and linear interpolation of
> the diode circuit characteristic. --| --| Parameters: --| AdcCount
> Raw ADC count. --| --| Returns: --| Temperature in �C x 10.
> INVALID_TEMPERATURE if out of range. --| --| Note: GNAT-GPL-2006
> compiler on Windows was used 
> -----------------------------------------------------------------------
> 
Observe the 'specification' on this comment (not yours I know, but
rather a direct translation of the OP C code) and the implementation:


> function Measure_Temperature (Adc_Count : in Integer) return Integer
> is
[snipped]

I would have written this part (to be accord the spec):
> if (Adc_Count < MINIMUM_ADC_COUNT) then -- Underflow of ADC -
> saturate at minimum value Index := 0; elsif (Adc_Count >
> MAXIMUM_ADC_COUNT) then -- Overflow of ADC - saturate at maximum
> value Index := TEMPERATURE_TABLE_NUM_ENTRIES - 1;

this way:
         -- beware of line wrap in Usenet
	if Adc_Count < MINIMUM_ADC_COUNT or else Adc_Count >
	MAXIMUM_ADC_COUNT then
       return INVALID_TEMPERATURE;

> else -- Find the index of the table entry just below the ADC value 
> Index := (Adc_Count - MINIMUM_ADC_COUNT) / SPACING; end if;

and thus I would have put all the remaining of this code within the else
block above.