PUBLIC MeasureTemperature

//    1 typedef unsigned int    uint16_t;
//    2 typedef int             int16_t;
//    3 typedef unsigned char   uint8_t;
//    4 
//    5 #define MINIMUM_ADC_COUNT               220
//    6 #define MAXIMUM_ADC_COUNT               468
//    7 #define SPACING                         8
//    8 #define TEMPERATURE_TABLE_NUM_ENTRIES   32
//    9 
//   10 //----------------------------------------------------------------------
//   11 // MeasureTemperature
//   12 //
//   13 // Calculates the temperature in §C given the ADC count by lookup
//   14 // table and linear interpolation of the diode circuit characteristic.
//   15 //
//   16 // Parameters:
//   17 // AdcCount Raw ADC count.
//   18 //
//   19 // Returns:
//   20 // Temperature in degC x 10. INVALID_TEMPERATURE if out of range.
//   21 //--------------------------------------------------------------------- }

        SECTION `.text`:CODE:NOROOT(1)
        THUMB
//   22 uint16_t MeasureTemperature(uint16_t AdcCount)
//   23 {
//   24     uint8_t     Index;
//   25     uint16_t    InterpolationDistance;
//   26     uint16_t    TempDiff;
//   27     uint16_t    Temperature;
//   28     static const int16_t Table[] =
//   29     {
//   30         1171, 1116, 1061, 1006,  952,  899,  846,  793,  741,  689, 638,
//   31          588,  537,  488,  438,  389,  341,  293,  246,  199,  152, 106,
//   32           61,   16,  -29,  -73, -116, -160, -202, -244, -286, -327
//   33     };
//   34 
//   35 
//   36     // Index is the index into the table. Each table entry is 8 ADC
//   37     // counts higher than the last one, so subtract the offset and
//   38     // divide by 8 to find the table index. InterpolationDistance
//   39     // is the linear distance between the the table entry ADC count
//   40     // and the actual ADC count.
//   41     // Check range of AdcCount and saturate index if out of range.
//   42 
//   43     if (AdcCount < MINIMUM_ADC_COUNT)
MeasureTemperature:
        CMP      R0,#+220
        BCS.N    ??MeasureTemperature_0
//   44     {
//   45         // Underflow of ADC - saturate at minimum value
//   46         Index = 0;
        MOVS     R1,#+0
        B.N      ??MeasureTemperature_1
//   47     }
//   48     else if (AdcCount > MAXIMUM_ADC_COUNT)
??MeasureTemperature_0:
        CMP      R0,#+468
        BLS.N    ??MeasureTemperature_2
//   49     {
//   50         // Overflow of ADC - saturate at maximum value
//   51         Index = TEMPERATURE_TABLE_NUM_ENTRIES - 1;
        MOVS     R1,#+31
        B.N      ??MeasureTemperature_1
//   52     }
//   53     else
//   54     {
//   55         // Find the index of the table entry just below th e ADC value
//   56         Index = (AdcCount - MINIMUM_ADC_COUNT) / SPACING;
??MeasureTemperature_2:
        SUBS     R1,R0,#+220
        LSRS     R1,R1,#+3
//   57     }
//   58 
//   59     // Calculate the interpolation between the table entries either side of
//   60     // the ADC value. This is the remainder of the difference between the
//   61     // ADC count and the minimum temperature ADC count divided by the
//   62     // spacing between table entries. Since the spacing is a power of 2,
//   63     // this can be achieved by simply masking all but the bottom 3 bits.
//   64 
//   65     InterpolationDistance = (AdcCount - MINIMUM_ADC_COUNT) & (SPACING - 1);
??MeasureTemperature_1:
        SUBS     R0,R0,#+220
        ANDS     R0,R0,#0x7
//   66     TempDiff = (Table[Index] - Table[Index+1]);
        LDR.N    R2,??DataTable0
        UXTB     R1,R1            ;; ZeroExt  R1,R1,#+24,#+24
        LDR      R2,[R2, R1, LSL #+2]
        LDR.N    R3,??DataTable0
        UXTB     R1,R1            ;; ZeroExt  R1,R1,#+24,#+24
        ADDS     R3,R3,R1, LSL #+2
        LDR      R3,[R3, #+4]
        SUBS     R2,R2,R3
//   67 
//   68     // The temperature is then the base temperature minus the amount
//   69     // calculated by linear interpolation. The compiler is clever enough
//   70     // to know that dividing by 8 is a right shift of three bits.
//   71     Temperature = Table[Index] - ((TempDiff * InterpolationDistance) / SPACING);
        LDR.N    R3,??DataTable0
        UXTB     R1,R1            ;; ZeroExt  R1,R1,#+24,#+24
        LDR      R1,[R3, R1, LSL #+2]
        MUL      R0,R0,R2
        SUBS     R0,R1,R0, LSR #+3
//   72 
//   73     return Temperature;
        BX       LR               ;; return
//   74 }
        SECTION `.text`:CODE:NOROOT(2)
        SECTION_TYPE SHT_PROGBITS, 0
        DATA
??DataTable0:
        DC32     ??Table
        SECTION `.rodata`:CONST:REORDER:NOROOT(2)
??Table:
        DATA
        DC32 1171, 1116, 1061, 1006, 952, 899, 846, 793, 741, 689, 638, 588
        DC32 537, 488, 438, 389, 341, 293, 246, 199, 152, 106, 61, 16, -29, -73
        DC32 -116, -160, -202, -244, -286, -327

        SECTION `.text`:CODE:NOROOT(1)
        THUMB
        END