The main.cpp program below demonstrates a simple way to interface with the MMA8452 accelerometer. The function reads in the acceleration data in the X, Y, and Z directions and displays them through a serial com port on a PC. The Putty Output figure below shows the output of the accelerometer using Putty. The program also dims or brightens the mbed LEDs 1-3 based on whether or not they are at 'level'( 0 Gs) or above respectively. The video below previews the code in action.
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main.cpp
- Committer:
- ashleymills
- Date:
- 2014-03-05
- Revision:
- 2:0630128bdb32
- Parent:
- 1:e9981919b524
- Child:
- 3:2a8e59a590db
File content as of revision 2:0630128bdb32:
#include "mbed.h" #include "MMA8452.h" DigitalOut myled(LED1); Serial pc(USBTX,USBRX); #define LOG(...) pc.printf(__VA_ARGS__); pc.printf("\r\n"); #define LOGX(...) pc.printf(__VA_ARGS__); void printByte(char b) { LOG("%d%d%d%d%d%d%d%d", (b&0x80)>>7, (b&0x40)>>6, (b&0x20)>>5, (b&0x10)>>4, (b&0x08)>>3, (b&0x04)>>2, (b&0x02)>>1, (b&0x01) ); } void sampleMMA8452Raw(MMA8452 *acc, int nsamples) { int samples = 0; int bufLen = 6; char buffer[6]; memset(&buffer,0x00,bufLen); while(samples<nsamples) { if(!acc->isXYZReady()) { wait(0.01); continue; } memset(&buffer,0x00,bufLen); acc->readXYZRaw(buffer); LOGX("Sample %d of %d: ",samples,nsamples); for(int i=0; i<bufLen; i++) { LOGX("%.2x ",buffer[i]); } LOG(" "); samples++; } } void sampleMMA8452Counts(MMA8452 *acc, int nsamples) { int samples = 0; int bufLen = 6; char buffer[6]; int x = 0, y = 0, z = 0; memset(&buffer,0x00,bufLen); while(samples<nsamples) { if(!acc->isXYZReady()) { wait(0.01); continue; } memset(&buffer,0x00,bufLen); if(acc->readXYZCounts(&x,&y,&z)) { LOG("Error reading sample"); break; } LOG("Sample %d of %d: %d, %d, %d",samples,nsamples,x,y,z); samples++; } } void sampleMMA8452Gravities(MMA8452 *acc, int nsamples) { int samples = 0; int bufLen = 6; char buffer[6]; double x = 0, y = 0, z = 0; memset(&buffer,0x00,bufLen); while(samples<nsamples) { if(!acc->isXYZReady()) { wait(0.01); continue; } memset(&buffer,0x00,bufLen); if(acc->readXYZGravity(&x,&y,&z)) { LOG("Error reading sample"); break; } LOG("Sample %d of %d: %lf, %lf, %lf",samples,nsamples,x,y,z); samples++; } } int test() { MMA8452 acc(p28, p27, 40000); acc.debugRegister(MMA8452_CTRL_REG_1); LOG("Entering standby"); if(acc.standby()) { LOG("Error putting MMA8452 in standby"); return false; } acc.debugRegister(MMA8452_CTRL_REG_1); LOG("Activating MMA8452"); if(acc.activate()) { LOG("Error activating MMA8452"); return false; } char devID = 0; if(acc.getDeviceID(&devID)) { LOG("Error getting device ID"); return false; } LOG("DeviceID: 0x%x",devID); if(devID!=0x2a) { LOG("Error, fetched device ID: 0x%x does not match expected 0x2a",devID); return false; } else { LOG("Device ID OK"); } // test setting dynamic range MMA8452::DynamicRange setRange = MMA8452::DYNAMIC_RANGE_UNKNOWN; MMA8452::DynamicRange readRange = MMA8452::DYNAMIC_RANGE_UNKNOWN; for(int i=0; i<=(int)MMA8452::DYNAMIC_RANGE_8G; i++) { setRange = (MMA8452::DynamicRange)i; if(acc.setDynamicRange(setRange)) { LOG("Error setting dynamic range. Failing."); return false; } readRange = acc.getDynamicRange(); if(readRange!=setRange) { LOG("Read dynamic range: 0x%x does not match set: 0x%x",readRange,setRange); return false; } LOG("Success on dynamic range %d",i); } // test setting data rate for(int i=0; i<=(int)MMA8452::RATE_1_563; i++) { if(acc.setDataRate((MMA8452::DataRateHz)i)) { LOG("Error setting data rate. Failing."); return false; } if(acc.getDataRate()!=(MMA8452::DataRateHz)i) { LOG("Read data rate: 0x%x does not match set: 0x%x",acc.getDataRate(),(MMA8452::DataRateHz)i); return false; } LOG("Success on data rate %d",i); } // set bit depth to 8 and read some values LOG("Sampling at BIT_DEPTH_8"); acc.setBitDepth(MMA8452::BIT_DEPTH_8); sampleMMA8452Raw(&acc,10); // set bit depth to 12 and read some values LOG("Sampling at BIT_DEPTH_12"); acc.setDataRate(MMA8452::RATE_100); acc.setBitDepth(MMA8452::BIT_DEPTH_12); sampleMMA8452Raw(&acc,10); LOG("Sampling counts"); acc.setDynamicRange(MMA8452::DYNAMIC_RANGE_2G); sampleMMA8452Counts(&acc,100); LOG("Samping gravities"); acc.setBitDepth(MMA8452::BIT_DEPTH_8); acc.setDynamicRange(MMA8452::DYNAMIC_RANGE_4G); sampleMMA8452Gravities(&acc,2000); return true; } void loop() { while(1) { wait(1); } } void u16d(uint16_t n) { int shift = 16; uint16_t mask = 0x8000; while(--shift>=0) { LOGX("%d",(n&mask)>>shift); mask >>= 1; } LOG(" "); } int eightBitToSigned(char *buf) { return (int8_t)*buf; } int twelveBitToSigned(char *buf) { //LOG("Doing twos complement conversion for 0x%x 0x%x",buf[0],buf[1]); // cheat by using the int16_t internal type // all we need to do is convert to little-endian format and shift right int16_t x = 0; ((char*)&x)[1] = buf[0]; ((char*)&x)[0] = buf[1]; // note this only works because the below is an arithmetic right shift return x>>4; // for reference, here is the full conversion, in case you port this somewhere where the above won't work /* uint16_t number = 0x0000; //u16d(number); int negative = false; // bit depth 12, is spread over two bytes // put it into a uint16_t for easy manipulation number |= (buf[0]<<8); number |= buf[1]; // if this is a negative number take the twos complement if(number&0x8000) { negative = true; // flip all bits (doesn't matter about lower 4 bits) number ^= 0xFFFF; // add 1 (but do so in a way that deals with overflow and respects our current leftwise shift) number += 0x0010; } // shifting down the result by 4 bits gives us the absolute number number >>= 4; int result = number; if(negative) { result *= -1; } return result; */ } int twosCompTest() { u16d((int16_t)5); u16d((int16_t)-5); // 12 bits of number gives 2048 steps int16_t i = -2047; while(1) { //LOG("number: %d",i); //u16d(number); uint16_t shiftedNumber = i<<4; //LOG("shifted:"); //u16d(shiftedNumber); // ARM is little endian whereas 12 bit 2's comp rep is big endian uint16_t flippedNumber = 0x0000; //LOG("switching bytes"); //u16d(flippedNumber); ((char*)&flippedNumber)[0] = ((char*)&shiftedNumber)[1]; //u16d(flippedNumber); ((char*)&flippedNumber)[1] = ((char*)&shiftedNumber)[0]; //u16d(flippedNumber); int value = twelveBitToSigned((char*)&flippedNumber); //LOG("%d converts to %d",i,value); if(i!=value) { return false; } if(i==2047) { break; } i++; } int8_t n = -127; while(1) { int value = eightBitToSigned((char*)&n); //LOG("%d converts to %d",n,value); if(n!=value) { return false; } if(n==127) { break; } n++; } return true; } int main() { pc.baud(115200); LOG("Begin"); if(!twosCompTest()) { LOG("twos comp test failed"); loop(); } LOG("twos comp test passed"); //loop(); for(int i=0; i<20; i++) { LOG(" "); } if(!test()) { LOG("FAIL."); loop(); } LOG("Tests passed"); loop(); }