Hello!
As there are many microcontrollers in the 12-bit ADC range, another way to do it
is to use a multiplication instead of a division (if dividing by 10, use a coefficient
for 1/10). This way you can perform a division by 10 in a few clocks (I just tried
with MSP430 : 2 clocks for the multiplication by 1/10, and 2 to move the result)
and also 2 clocks for the x10 multiplication.
And the bonus: no huge lookup table, no endless if-else statements. It can be
written a little bit shorter at the expense of efficiency (with a loop).
Here is the trick. Example with a = 1234.
1. Divide by 10, obtain 123
2. Multiply 123 by 10, obtain 1230
3. Last digit is the original value (1234) to which 1230 has been subtracted.
4. Set the original value to 123, repeat the trick until done.
As for the code (see below), without further optimization than the normal one (low optimization),
I get 100 clocks for this method, vs 82 ~ 91 for the half interval method above. The variation
is due to the number of if..else needed for a given number.
BUT: this method can translate any number from 0 to 9999, so the range is twice the
half-interval method.
NB: This code is not portable. It is efficient because of the hardware multiplier.
It can be done without hardware multiplier by using 32 bit multiplications and would
also be quite fast, I believe.
| Code C - [expand] |
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| #include "MSP430F5529.h"
#include "Types.h"
void adc2ascii(uint16 value, char *str) ;
void IToA(uint16 value, char * str);
char str1[6];
char str2[6];
void main(void) {
uint16 i;
uint16 div10, trick10;
MPY = 6554;
for(i = 100 ; i < 200 ; ++i) {
IToA(i, str1); // Runs in 100 clocks for range [0..9999] (*)
adc2ascii(i, str2); // Runs in 82 to 91 clocks for range [0..4999]
}
}
// (*) The above figures are given for MSP430F5529, IAR compiler, with low optimization
//
void IToA(uint16 value, char * str) {
// Get d0
MPY = 6554; // Divide by 10
OP2 = value; // Example val = 1234
MPY=10; // Multiply by 10
OP2 = RES1; // Recycle last result as an operand to multiply it back by 10
str[3] = '0' + value - RES0;
value = OP2; // Use last operand (that was divided by 10 as a new value, and do the same stuff again.
MPY = 6554;
OP2 = value;
MPY=10;
OP2=RES1;
str[2] = '0' + value - RES0;
value = OP2;
MPY = 6554;
OP2 = value;
str[0] = '0' + RES1;
MPY=10;
OP2=RES1;
str[1] = '0' + value - RES0;
}
void adc2ascii(uint16 value, char *str) {
char *p = str;
if (value > 2999) {
if (value > 3999) {
*p++ = '4';
value -= 4000;
}
else {
*p++ = '3';
value -= 3000;
}
}
else {
if(value > 1999) {
*p++ = '2';
value -= 2000;
}
else if(value > 999) {
*p++ = '1';
value -= 1000;
}
else {
*p++ = '0';
}
}
if (value > 499) {
if (value > 699) {
if (value > 899) {
*p++ = '9';
value -= 900;
}
else if (value > 799) {
*p++ = '8';
value -= 800;
}
else {
*p++ = '7';
value -= 700;
}
}
else {
if (value > 599) {
*p++ = '6';
value -= 600;
}
else {
*p++ = '5';
value -= 500;
}
}
}
else {
if (value > 299) {
if (value > 399) {
*p++ = '4';
value -= 400;
}
else {
*p++ = '3';
value -= 300;
}
}
else {
if (value > 199) {
*p++ = '2';
value -= 200;
}
else if (value > 99) {
*p++ = '1';
value -= 100;
}
else {
*p++ = '0';
}
}
}
if (value > 49) {
if (value > 69) {
if (value > 89) {
*p++ = '9';
value -= 90;
}
else if (value > 79) {
*p++ = '8'; value -= 80;
}
else {
*p++ = '7';
value -= 70;
}
}
else {
if (value > 59) {
*p++ = '6';
value -= 60;
}
else {
*p++ = '5';
value -= 50;
}
}
}
else {
if (value > 19) {
if (value > 39) {
*p++ = '4';
value -= 40;
}
else if (value > 29) {
*p++ = '3';
value -= 30;
}
else {
*p++ = '2';
value -= 20;
}
}
else {
if (value > 9) { *p++ = '1'; value -= 10; }
else if (p != str) { *p++ = '0'; }
}
}
*p++ = value + '0';
*p = 0;
} |
Dora.