6 Appendix: Q App Source Code

This utility can be used for temperature conversion of any Q format encoding. This code is written and tested for a Unix-like shell. We recommend to save the source code as q.c and compile the code using cc q.c -o qapp.

#include <stdio.h>
#include <unistd.h>

void main(int argc, char *argv[])
{
	int c;
	uint8_t bits = 16;
	uint8_t qnum = 7;
	uint8_t byte1;
	uint8_t byte2;
	int16_t data;
	int mode = 0;
	while ((c = getopt(argc, argv, "b:q:hx")) != -1)
		switch (c)
		{
		case 'b':
			sscanf(optarg, "%hhi", &bits);
			break;
		case 'q':
			sscanf(optarg, "%hhi", &qnum);
			break;
		case 'h':
			mode = 1; /* print help */
			break;
		case 'x':
			mode = 2; /* print example code */
		}
	uint8_t shift = 16 - bits;
	float resolution = (float)1 / (1 << qnum);
	/* recommend using a constant for resolution in application code */
	if (mode == 0)
	{ /* parse byte(s) and print celsius */
		switch (argc - optind)
		{
		case 2:
			sscanf(argv[optind], "%hhi", &byte1);
			sscanf(argv[optind + 1], "%hhi", &byte2);
			data = (int8_t)byte1 << 8 | byte2;
			printf("input: %d (0x%hhX) and %d (0x%hhX) becomes %d (0x%hX)\n", byte1, byte1, byte2, byte2, data, data);
			break;
		case 1:
			sscanf(argv[optind], "%hi", &data);
			printf("input: %d (0x%hX) is assumed to be 16-bit\n", data, data);
			break;
		case 0:
			data = 0x7FFF;
			printf("demo: %d (0x%hX)\n", data, data);
			break;
		}
		printf("%d-bit format will have %d bits discarded by right shift\n", bits, shift);
		data >>= shift;
		printf("q%d is %f resolution\n", qnum, resolution);
		float f = data * resolution;
		printf("float: %f C\n", f);
		/* preserve fractional result while using int only */
		int mC = data * 1000 >> qnum;
		printf("int: %d mC\n", mC);
		/* discard fractional result while using int only */
		int C = data >> qnum;
		printf("int: %d C\n", C);
	}
	else if (mode == 1) /* print help */
	{
		printf("qapp [-b bits] [-q qnum] [byte] [byte2]\n\
use -b to specify number of bits\n\
use -q to specify Q format, which describes resolution\n\
byte can be 16 bit data or the first of two 8 bit bytes\n\
byte2 is the second 8 bit byte that will be assembled with byte\n\
\n\
Device settings:\n\
TMP117, TMP114:\n\
 qapp -b 16 -q 7 0x0C80\n\
TMP102, TMP112, TMP1075:\n\
 qapp -b 12 -q 4 0x1900\n\
TMP102, TMP112 EM=1:\n\
 qapp -b 13 -q 4 0x0C80\n\
TMP468:\n\
 qapp -b 13 -q 4 0x0C80\n\
TMP107:\n\
 qapp -b 14 -q 6 0x1900\n\
TMP126:\n\
 qapp -b 14 -q 5 0x0C80\n\
");
	}
	else if (mode == 2) /* print example code */
	{
		/* use 24.5 to represent nominal, ambient temperature with the first fractional bit set */
		int16_t exdata = 24.5f / resolution;
		exdata <<= shift;
		printf("C Code Examples:\n");
		printf("/* %d-bit format will have %d bits discarded by right shift\n", bits, shift);
		printf("   q%d is %f resolution\n", qnum, resolution);
		printf("   the following bytes represent 24.5C */ \n");
		printf("uint8_t byte1 = 0x%hhX;\n", exdata >> 8);
		printf("uint8_t byte2 = 0x%hhX;\n", exdata);
		if (shift)
			printf("float f = (((int8_t) byte1 << 8 | byte2) >> %d) * %gf;\n", shift, resolution);
		else
			printf("float f = ((int8_t) byte1 << 8 | byte2) * %gf;\n", resolution);
		if (shift)
			printf("int mC = (((int8_t) byte1 << 8 | byte2) >> %d) * 1000 >> %d;\n", shift, qnum);
		else
			printf("int mC = ((int8_t) byte1 << 8 | byte2) * 1000 >> %d;\n", qnum);
		if (shift + qnum == 8)
			printf("int C = (int8_t) byte1;\n");
		else if (shift)
			printf("int C = (((int8_t) byte1 << 8 | byte2) >> %d) >> %d;\n", shift, qnum);
		else
			printf("int C = ((int8_t) byte1 << 8 | byte2) >> %d;\n", qnum);
	}
}