RE: Translating an embedded C algorithm

["Vo, Anh \(US SSA\)" <anh.vo@baesystems.com>]

-----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.

   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.

------------------------------------------------------------------------
--| MeasureTemperature
--|
--| Calculates the temperature in ºC given the ADC count by lookup
--| table and linear interpolation of the diode circuit characteristic.
--|
--| Parameters:
--| AdcCount Raw ADC count.
--|
--| Returns:
--| Temperature in ºC x 10. INVALID_TEMPERATURE if out of range.
--| 
--| Note: GNAT-GPL-2006 compiler on Windows was used
-------------------------------------------------------------------------
function Measure_Temperature (Adc_Count : in Integer) return Integer is

   Index : Integer := 0;
   InterpolationDistance : Integer := 0;
   TempDiff : Integer := 0;
   TempCalOffset : Integer := 0;
   Temperature : Integer := 0;
   
   TEMPERATURE_TABLE_NUM_ENTRIES : constant := 32;
   Table : constant array (0 .. TEMPERATURE_TABLE_NUM_ENTRIES - 1) of Integer :=
                               (1171, 1116, 1061, 1006, 952,   899,  846,  793,
                                 741,  689,  638,  588, 537,   488,  438,  389,
                                 341,  293,  246,  199, 152,   106,   61,   16,
                                 -29,  -73, -116, -160, -202, -244, -286, -327);

   MINIMUM_ADC_COUNT : constant := 220;
   MAXIMUM_ADC_COUNT : constant := 246;
   SPACING : constant := 8; 
   TEMPERATURE_CAL_VALUE : constant := 0;

   -- *** Important Note: 
   -- The algorithm of the following function needs to be defined.
   function ReadEEPROM (Temp : in Integer) return Integer is
   begin
      return Temp; -- for now
   end ReadEEPROM;
   -----------------------------------------------------------
   
begin
   
   -- Index is the index into the table. Each table entry is 8 ADC
   -- counts higher than the last one, so subtract the offset and
   -- divide by 8 to find the table index. InterpolationDistance
   -- is the linear distance between the the table entry ADC cou nt
   -- and the actual ADC count.
   -- Check range of Adc_Count and saturate index if out of range.
   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;
   else
      -- Find the index of the table entry just below the ADC value
      Index := (Adc_Count - MINIMUM_ADC_COUNT) / SPACING;
   end if;
   
   -- Calculate the interpolation between the table entries either side of
   -- the ADC value. This is the remainder of the difference between the
   -- ADC count and the minimum temperature ADC count divided by the
   -- spacing between table entries. Since the spacing is a power of 2,
   -- this can be achieved by simply masking all but the bottom 3 bits.
   InterpolationDistance := (Adc_Count - MINIMUM_ADC_COUNT) mod (SPACING - 1);
   TempDiff := (Table(Index) - Table (Index+1));
   
   -- The temperature is then the base temperature minus the amount
   -- calculated by linear interpolation. The compiler is clever enough
   -- to know that dividing by 8 is a right shift of three bits.
   Temperature := Table(Index) - ((TempDiff * InterpolationDistance) / SPACING);
   
   -- To this is then added the calibration offset to the temperature table.
   TempCalOffset := ReadEeprom (TEMPERATURE_CAL_VALUE);
   Temperature := Temperature + TempCalOffset;
   
   return Temperature;
        
end Measure_Temperature;