DCSS504 - A class and a demo program to use with the DC-SS5…

Users » igorsk » Code » DCSS504

Igor Skochinsky / Mbed 2 deprecated DCSS504

A class and a demo program to use with the DC-SS504 board from SureElectronics which uses MMC2120MG magnetometer from Memsic. The program glows leds depending on the direction it is turned to.

Dependencies: mbed

MMCx12xM.cpp@0:a44429321af8, 2009-12-02 (annotated)

Committer:: igorsk
Date:: Wed Dec 02 23:03:25 2009 +0000
Revision:: 0:a44429321af8

Who changed what in which revision?

User	Revision	Line number	New contents of line
igorsk	0:a44429321af8	1	#include "MMCx12xM.h"
igorsk	0:a44429321af8	2	#include <stdarg.h>
igorsk	0:a44429321af8	3	#include <limits.h>
igorsk	0:a44429321af8	4
igorsk	0:a44429321af8	5	/*
igorsk	0:a44429321af8	6
igorsk	0:a44429321af8	7	Memsic datasheets use very obtuse language, here I tried to summarize it in plain English.
igorsk	0:a44429321af8	8
igorsk	0:a44429321af8	9	The device works over I2C ("fast" mode, i.e. 400 kHz max)
igorsk	0:a44429321af8	10	the slave address is determined by the last digit (x in MMC212x) :
igorsk	0:a44429321af8	11	0: 0x60, 1: 0x64, 2: 0x68, 3: 0x6C
igorsk	0:a44429321af8	12
igorsk	0:a44429321af8	13	Register map:
igorsk	0:a44429321af8	14	00 control register
igorsk	0:a44429321af8	15	01 most significant byte x axis
igorsk	0:a44429321af8	16	02 least significant byte x axis
igorsk	0:a44429321af8	17	03 most significant byte y axis
igorsk	0:a44429321af8	18	04 least significant byte y axis
igorsk	0:a44429321af8	19	05 most significant byte z axis (MMC312xM only)
igorsk	0:a44429321af8	20	06 least significant byte z axis (MMC312xM only)
igorsk	0:a44429321af8	21
igorsk	0:a44429321af8	22	Operation is initiated by sending the register address (must be 0, since
igorsk	0:a44429321af8	23	only control register is writable) and then the command code, which is one
igorsk	0:a44429321af8	24	of the bits from the control register.
igorsk	0:a44429321af8	25
igorsk	0:a44429321af8	26	Control register layout:
igorsk	0:a44429321af8	27	bit 0: TM (take measurements)
igorsk	0:a44429321af8	28	set to get measurements (i.e. send 0x01)
igorsk	0:a44429321af8	29	bit is reset when measurement is done, so you can use it
igorsk	0:a44429321af8	30	to check if the operation is finished
igorsk	0:a44429321af8	31	bit 1: SET (set coil)
igorsk	0:a44429321af8	32	set to send a large current through the set/reset coil
igorsk	0:a44429321af8	33	should be done if sensor was affected by a large magnetic field (>5.5 gauss)
igorsk	0:a44429321af8	34	also after power on
igorsk	0:a44429321af8	35	result can be checked same as above
igorsk	0:a44429321af8	36	bit 2: RESET (reset coil)
igorsk	0:a44429321af8	37	same as above but sends current in the opposite direction
igorsk	0:a44429321af8	38	set/reset should be interleaved in "low-power mode", whatever that is
igorsk	0:a44429321af8	39	bits 3-6: reserved
igorsk	0:a44429321af8	40	bit 7: not described
igorsk	0:a44429321af8	41
igorsk	0:a44429321af8	42	To read a register, write its address and then read the value. The address auto-increments
igorsk	0:a44429321af8	43	after reading, so it's not necessary to send it again if reading sequentially. The address
igorsk	0:a44429321af8	44	is reset to 0 on power-on.
igorsk	0:a44429321af8	45
igorsk	0:a44429321af8	46	Taking measurements works like following:
igorsk	0:a44429321af8	47	1. write 0 (control register address), then 0x01 (take measurements)
igorsk	0:a44429321af8	48	2. wait 5ms for the measurement to complete
igorsk	0:a44429321af8	49	3. write 0 again (control register address), then read the register value
igorsk	0:a44429321af8	50	4. check if the bit 0 is cleared. If not, repeat from 3.
igorsk	0:a44429321af8	51	5. read x msb
igorsk	0:a44429321af8	52	6. read x lsb
igorsk	0:a44429321af8	53	7. read y msb
igorsk	0:a44429321af8	54	8. read y lsb
igorsk	0:a44429321af8	55	9. (if MMC312xM) read z msb
igorsk	0:a44429321af8	56	10. (if MMC312xM) read z lsb
igorsk	0:a44429321af8	57
igorsk	0:a44429321af8	58	N.B.: ADC resolution is only 12 bits, so four high bits of values will be 0
igorsk	0:a44429321af8	59
igorsk	0:a44429321af8	60	You can also skip some values and read directly the value wanted
igorsk	0:a44429321af8	61	by sending its address before reading.
igorsk	0:a44429321af8	62	*/
igorsk	0:a44429321af8	63
igorsk	0:a44429321af8	64	// uncomment to show protocol debug tracing
igorsk	0:a44429321af8	65	//#define DEBUG
igorsk	0:a44429321af8	66
igorsk	0:a44429321af8	67	int dprintf(const char *fmt, ...)
igorsk	0:a44429321af8	68	{
igorsk	0:a44429321af8	69	#ifdef DEBUG
igorsk	0:a44429321af8	70	va_list args;
igorsk	0:a44429321af8	71	va_start (args, fmt);
igorsk	0:a44429321af8	72	int ret = vprintf(fmt, args);
igorsk	0:a44429321af8	73	va_end(args);
igorsk	0:a44429321af8	74	return ret;
igorsk	0:a44429321af8	75	#else
igorsk	0:a44429321af8	76	return 0;
igorsk	0:a44429321af8	77	#endif
igorsk	0:a44429321af8	78	}
igorsk	0:a44429321af8	79
igorsk	0:a44429321af8	80	enum command {
igorsk	0:a44429321af8	81	TM = 1, // take measurements
igorsk	0:a44429321af8	82	SET = 2, // set
igorsk	0:a44429321af8	83	RESET = 4 // reset
igorsk	0:a44429321af8	84	};
igorsk	0:a44429321af8	85
igorsk	0:a44429321af8	86	MMCx12xM::MMCx12xM(I2C &i2c, int address, const char *name) : Base(name),
igorsk	0:a44429321af8	87	_I2C(&i2c), _addr(address), _own_i2c(false)
igorsk	0:a44429321af8	88	{
igorsk	0:a44429321af8	89	}
igorsk	0:a44429321af8	90
igorsk	0:a44429321af8	91	MMCx12xM::MMCx12xM(PinName sda, PinName scl, int address, const char *name) : Base(name),
igorsk	0:a44429321af8	92	_addr(address)
igorsk	0:a44429321af8	93	{
igorsk	0:a44429321af8	94	_I2C = new I2C(sda, scl);
igorsk	0:a44429321af8	95	// we own the bus, so we can set frequency
igorsk	0:a44429321af8	96	// MMCx12x claims to handle 400 kHz
igorsk	0:a44429321af8	97	_I2C->frequency(400000);
igorsk	0:a44429321af8	98	_own_i2c = true;
igorsk	0:a44429321af8	99	}
igorsk	0:a44429321af8	100
igorsk	0:a44429321af8	101	MMCx12xM::~MMCx12xM()
igorsk	0:a44429321af8	102	{
igorsk	0:a44429321af8	103	if (_own_i2c)
igorsk	0:a44429321af8	104	delete _I2C;
igorsk	0:a44429321af8	105	}
igorsk	0:a44429321af8	106
igorsk	0:a44429321af8	107	// send the specified command: write it into the control register
igorsk	0:a44429321af8	108	bool MMCx12xM::_send_command(int command)
igorsk	0:a44429321af8	109	{
igorsk	0:a44429321af8	110	dprintf("* send command %d\n", command);
igorsk	0:a44429321af8	111	const char writecmd[] = {0, command}; // address: 0 (control reg)
igorsk	0:a44429321af8	112	int res = _I2C->write(_addr, writecmd, 2);
igorsk	0:a44429321af8	113	dprintf("write: %d\n", res);
igorsk	0:a44429321af8	114	return res == 0;
igorsk	0:a44429321af8	115	}
igorsk	0:a44429321af8	116
igorsk	0:a44429321af8	117	// wait until the command is done
igorsk	0:a44429321af8	118	// this is signalled by clearing of the
igorsk	0:a44429321af8	119	// corresponding bit in the control register
igorsk	0:a44429321af8	120	bool MMCx12xM::_wait_ready(int command)
igorsk	0:a44429321af8	121	{
igorsk	0:a44429321af8	122	dprintf("* wait ready %d\n", command);
igorsk	0:a44429321af8	123	const char writecmd = 0; // set read address to 0 (control reg)
igorsk	0:a44429321af8	124	int res = _I2C->write(_addr, &writecmd, 1);
igorsk	0:a44429321af8	125	dprintf(" write: %d\n", res);
igorsk	0:a44429321af8	126	if ( res != 0 )
igorsk	0:a44429321af8	127	return false;
igorsk	0:a44429321af8	128	char reg;
igorsk	0:a44429321af8	129	while ( 1 )
igorsk	0:a44429321af8	130	{
igorsk	0:a44429321af8	131	// read control register value
igorsk	0:a44429321af8	132	res = _I2C->read(_addr, &reg, 1);
igorsk	0:a44429321af8	133	dprintf(" read: %d, reg=%08X\n", res, reg);
igorsk	0:a44429321af8	134	if ( res != 0 )
igorsk	0:a44429321af8	135	return false;
igorsk	0:a44429321af8	136	// check if the command bit is cleared
igorsk	0:a44429321af8	137	if ( (reg & command) == 0 )
igorsk	0:a44429321af8	138	break; // data ready
igorsk	0:a44429321af8	139	dprintf("* Not ready, try again\n");
igorsk	0:a44429321af8	140	// otherwise tell the device that we want to read the register (address 0) again
igorsk	0:a44429321af8	141	res = _I2C->write(_addr, &writecmd, 1);
igorsk	0:a44429321af8	142	dprintf(" write: %d\n", res);
igorsk	0:a44429321af8	143	if ( res != 0 )
igorsk	0:a44429321af8	144	return false;
igorsk	0:a44429321af8	145	}
igorsk	0:a44429321af8	146	return true;
igorsk	0:a44429321af8	147	}
igorsk	0:a44429321af8	148
igorsk	0:a44429321af8	149	// read one axis value (two bytes)
igorsk	0:a44429321af8	150	// set read address if index specified explicitly
igorsk	0:a44429321af8	151	bool MMCx12xM::_read_axis(int *axis, int index)
igorsk	0:a44429321af8	152	{
igorsk	0:a44429321af8	153	dprintf("* read axis %d\n", index);
igorsk	0:a44429321af8	154	// accept only x, y or z (0, 1, 2)
igorsk	0:a44429321af8	155	if ( index > 2 )
igorsk	0:a44429321af8	156	return false;
igorsk	0:a44429321af8	157	int res;
igorsk	0:a44429321af8	158	if ( index != - 1 )
igorsk	0:a44429321af8	159	{
igorsk	0:a44429321af8	160	const char writecmd = index*2 + 1; // set read address for the axis value
igorsk	0:a44429321af8	161	res = _I2C->write(_addr, &writecmd, 1);
igorsk	0:a44429321af8	162	dprintf(" write: %d\n", res);
igorsk	0:a44429321af8	163	if ( res != 0 )
igorsk	0:a44429321af8	164	return false;
igorsk	0:a44429321af8	165	}
igorsk	0:a44429321af8	166	uint8_t pair[2]; // msb, lsb
igorsk	0:a44429321af8	167	res = _I2C->read(_addr, (char*)&pair, 2);
igorsk	0:a44429321af8	168	dprintf(" read: %d, msb=%02X, lsb=%02X\n", res, pair[0], pair[1]);
igorsk	0:a44429321af8	169	if ( res != 0 )
igorsk	0:a44429321af8	170	return false;
igorsk	0:a44429321af8	171	// make an integer from msb and lsb
igorsk	0:a44429321af8	172	*axis = (pair[0] << 8) \| pair[1];
igorsk	0:a44429321af8	173	return true;
igorsk	0:a44429321af8	174	}
igorsk	0:a44429321af8	175
igorsk	0:a44429321af8	176	// ask chip to take measurements and
igorsk	0:a44429321af8	177	// read specified number of raw axis values
igorsk	0:a44429321af8	178	bool MMCx12xM::read_raw_values(int *values, int count)
igorsk	0:a44429321af8	179	{
igorsk	0:a44429321af8	180	dprintf("* read_raw_values\n");
igorsk	0:a44429321af8	181	if ( !_send_command(TM) )
igorsk	0:a44429321af8	182	{
igorsk	0:a44429321af8	183	dprintf(" send_command(TM) failed\n");
igorsk	0:a44429321af8	184	return false;
igorsk	0:a44429321af8	185	}
igorsk	0:a44429321af8	186	wait_ms(5);
igorsk	0:a44429321af8	187	if ( !_wait_ready(TM) )
igorsk	0:a44429321af8	188	{
igorsk	0:a44429321af8	189	dprintf(" wait_ready(TM) failed\n");
igorsk	0:a44429321af8	190	return false;
igorsk	0:a44429321af8	191	}
igorsk	0:a44429321af8	192	// we have read the control register, so continue reading the data
igorsk	0:a44429321af8	193	// which will be the axis values
igorsk	0:a44429321af8	194	for ( int i=0; i < count; i++ )
igorsk	0:a44429321af8	195	{
igorsk	0:a44429321af8	196	// we're reading values sequentially, so no need to set the index
igorsk	0:a44429321af8	197	if ( !_read_axis(&values[i]) )
igorsk	0:a44429321af8	198	{
igorsk	0:a44429321af8	199	dprintf(" _read_axis() failed\n");
igorsk	0:a44429321af8	200	return false;
igorsk	0:a44429321af8	201	}
igorsk	0:a44429321af8	202	}
igorsk	0:a44429321af8	203	return true;
igorsk	0:a44429321af8	204	}
igorsk	0:a44429321af8	205
igorsk	0:a44429321af8	206	bool MMCx12xM::coil_set()
igorsk	0:a44429321af8	207	{
igorsk	0:a44429321af8	208	return _send_command(SET) && _wait_ready(SET);
igorsk	0:a44429321af8	209	}
igorsk	0:a44429321af8	210
igorsk	0:a44429321af8	211	bool MMCx12xM::coil_reset()
igorsk	0:a44429321af8	212	{
igorsk	0:a44429321af8	213	return _send_command(SET) && _wait_ready(SET);
igorsk	0:a44429321af8	214	}
igorsk	0:a44429321af8	215
igorsk	0:a44429321af8	216	void MMCx12xM::calibrate_begin()
igorsk	0:a44429321af8	217	{
igorsk	0:a44429321af8	218	// begin calibration: init the values arrays
igorsk	0:a44429321af8	219	for ( int i=0; i < 3; i++ )
igorsk	0:a44429321af8	220	{
igorsk	0:a44429321af8	221	_maxvals[i] = 0;
igorsk	0:a44429321af8	222	_minvals[i] = INT_MAX;
igorsk	0:a44429321af8	223	}
igorsk	0:a44429321af8	224	}
igorsk	0:a44429321af8	225
igorsk	0:a44429321af8	226	void MMCx12xM::calibrate_step(int count)
igorsk	0:a44429321af8	227	{
igorsk	0:a44429321af8	228	// take a measurement and update min-max values
igorsk	0:a44429321af8	229	int values[3];
igorsk	0:a44429321af8	230	if ( read_raw_values(values, count) )
igorsk	0:a44429321af8	231	{
igorsk	0:a44429321af8	232	for ( int i=0; i < count; i++ )
igorsk	0:a44429321af8	233	{
igorsk	0:a44429321af8	234	if ( _maxvals[i] < values[i] )
igorsk	0:a44429321af8	235	_maxvals[i] = values[i];
igorsk	0:a44429321af8	236	if ( _minvals[i] > values[i] )
igorsk	0:a44429321af8	237	_minvals[i] = values[i];
igorsk	0:a44429321af8	238	}
igorsk	0:a44429321af8	239	}
igorsk	0:a44429321af8	240	}
igorsk	0:a44429321af8	241
igorsk	0:a44429321af8	242	void MMCx12xM::calibrate_end()
igorsk	0:a44429321af8	243	{
igorsk	0:a44429321af8	244	// calculate sensitivity and offset for each axis
igorsk	0:a44429321af8	245	// see Memsic app note AN-00MM-003
igorsk	0:a44429321af8	246	dprintf("* calibration end\n");
igorsk	0:a44429321af8	247	for ( int i=0; i < 3; i++ )
igorsk	0:a44429321af8	248	{
igorsk	0:a44429321af8	249	_sensitivity[i] = (_maxvals[i] - _minvals[i]) / 2;
igorsk	0:a44429321af8	250	_offset[i] = (_maxvals[i] + _minvals[i]) / 2;
igorsk	0:a44429321af8	251	dprintf(" %i: min = %d, max = %d, s = %d, o = %d\n", i, _minvals[i], _maxvals[i], _sensitivity[i], _offset[i]);
igorsk	0:a44429321af8	252	}
igorsk	0:a44429321af8	253	}
igorsk	0:a44429321af8	254
igorsk	0:a44429321af8	255	bool MMCx12xM::read_values(float *values, int count)
igorsk	0:a44429321af8	256	{
igorsk	0:a44429321af8	257	int rvalues[3];
igorsk	0:a44429321af8	258	if ( read_raw_values(rvalues, count) )
igorsk	0:a44429321af8	259	{
igorsk	0:a44429321af8	260	// transform into calibrated values in the range -1.0 .. +1.0
igorsk	0:a44429321af8	261	for ( int i=0; i < count; i++ )
igorsk	0:a44429321af8	262	{
igorsk	0:a44429321af8	263	// NB: we use a temp float so that the division is not integer
igorsk	0:a44429321af8	264	float d = (rvalues[i] - _offset[i]);
igorsk	0:a44429321af8	265	values[i] = d / _sensitivity[i];
igorsk	0:a44429321af8	266	}
igorsk	0:a44429321af8	267	return true;
igorsk	0:a44429321af8	268	}
igorsk	0:a44429321af8	269	return false;
igorsk	0:a44429321af8	270	}

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Type:	Program
Mbed OS support:	Mbed 2 deprecated
Created:	02 Dec 2009
Imports:	6
Forks:	0
Commits:	1
Dependents:	0
Dependencies:	1
Followers:	3

MMCx12xM.cpp@0:a44429321af8, 2009-12-02 (annotated)

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