[2024-feb-29] Sad news: Eric Layton aka Nocturnal Slacker aka vtel57 passed away on Feb 26th, shortly after hospitalization. He was one of our Wiki's most prominent admins. He will be missed.
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interfacing_i2c_devices [2014/04/03 21:25 (UTC)] – [Communicating With An I2C Device] louigi600 | howtos:hardware:arm:interfacing_i2c_devices [2023/05/28 13:16 (UTC)] – [Voltage Level Shifting] louigi600 | ||
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====== Preface ====== | ====== Preface ====== | ||
- | Most modern PC have several internal components that communicate vital information, | + | Most modern PC have several internal components that communicate vital information, |
+ | Should you want to hack one of the many I2C busses on your PC the easiest one to access is the one in the DIMM modules. Modern DIMM modules have an I2C eprom in them that the bios reads to find out the characteristics of the DIMM module. Since the DIMM module can be removed from PC and hacked separately without risking to damage permanently your PC it is probably your safest option. | ||
====== Preparing Your Host System ====== | ====== Preparing Your Host System ====== | ||
Line 18: | Line 20: | ||
===== Detecting Connected Devices ===== | ===== Detecting Connected Devices ===== | ||
- | There are probably many ways to determine what's connected to an I2C bus, I chose to use stuff out of the [[http:// | + | There are probably many ways to determine what's connected to an I2C bus, I chose to use stuff out of the [[http:// |
First thing you want to know is what I2C busses are present on your system as there may be more then one and looking in the wrong bus may be frustrating: | First thing you want to know is what I2C busses are present on your system as there may be more then one and looking in the wrong bus may be frustrating: | ||
Line 139: | Line 141: | ||
I hate showing my poor C programming capabilities but here's some code that uses i2c-dev to read stuff from the ITG3200 and takes an average over 10 readings: | I hate showing my poor C programming capabilities but here's some code that uses i2c-dev to read stuff from the ITG3200 and takes an average over 10 readings: | ||
- | |||
- | #include < | ||
- | #include < | ||
- | #include < | ||
- | #include < | ||
- | #include < | ||
- | #include < | ||
- | #include < | ||
- | #include < | ||
- | #include < | ||
- | | ||
- | #define I2C_DEVICE "/ | ||
- | #define I2C_DEV_ADDR 0x69 | ||
- | #define I2C_DEV_SELF 0x0 | ||
- | #define I2C_DEV_INT 0x1a | ||
- | #define I2C_DEV_REG_START_ADDR 0x1b | ||
- | #define I2C_DEV_REG_END_ADDR 0x22 | ||
- | | ||
- | #define TEMP_RAW_OFFSET 13200 | ||
- | #define TEMP_RAW_SENSITIVITY 280 | ||
- | #define TEMP_OFFSET 35 | ||
- | | ||
- | #define ROT_RAW_SENSITIVITY 14.375 | ||
- | | ||
- | void read_registers (int file, int *raw) | ||
- | { char buf[256] = {0}; | ||
- | int i,j,k; | ||
- | | ||
- | /*For some unexpected reason I'm getting responses from the other I2C devices | ||
- | on the same bus so I'm ignoring data that does not match the WHO AM I reg | ||
- | and also data that has not set the interrupt register (meaning that data is | ||
- | not really avalible) | ||
- | */ | ||
- | while (buf[0] != 0x69 || buf[26] == 0) | ||
- | { if (read(file, | ||
- | { /* ERROR HANDLING: i2c transaction failed */ | ||
- | printf(" | ||
- | exit(1); | ||
- | } | ||
- | } | ||
- | | ||
- | j=0; | ||
- | for(i=I2C_DEV_REG_START_ADDR; | ||
- | { k= (buf[i] << 8) + buf[i+1]; | ||
- | if ( k > 32768 ) *(raw+j)= k - 65536; | ||
- | else *(raw+j)=k; | ||
- | i++; | ||
- | j++; | ||
- | } | ||
- | } | ||
- | | ||
- | main () | ||
- | { int file, | ||
- | int i,j,k; | ||
- | int raw_data[4]; | ||
- | float data[4], | ||
- | char buf[256] = {0}; | ||
- | | ||
- | if ((file = open(I2C_DEVICE, | ||
- | { /* ERROR HANDLING: you can check errno to see what went wrong */ | ||
- | perror(" | ||
- | exit(1); | ||
- | } | ||
- | | ||
- | if (ioctl(file, | ||
- | { printf(" | ||
- | /* ERROR HANDLING; you can check errno to see what went wrong */ | ||
- | exit(1); | ||
- | } | ||
- | | ||
- | for(i=0; | ||
- | { read_registers(file,& | ||
- | tdata[i]=TEMP_OFFSET + (((float)raw_data[0] + TEMP_RAW_OFFSET) / TEMP_RAW_SENSITIVITY); | ||
- | rxdata[i]=(float)raw_data[1]/ | ||
- | rydata[i]=(float)raw_data[2]/ | ||
- | rzdata[i]=(float)raw_data[3]/ | ||
- | } | ||
- | close(file); | ||
- | | ||
- | for(i=0; | ||
- | { data[0]=data[0] + tdata[i]; | ||
- | data[1]=data[1] + rxdata[i]; | ||
- | data[2]=data[2] + rydata[i]; | ||
- | data[3]=data[3] + rzdata[i]; | ||
- | } | ||
- | for(i=0; | ||
- | | ||
- | printf(" | ||
- | printf(" | ||
- | printf(" | ||
- | printf(" | ||
- | } | ||
- | |||
- | With some help from LQ forum I realized that it's a bad idea to bulk dump the whole register set, instaad it's better to probe each register separately. The code that follows does not yet make the avarage like the one above bit it takes 10 consecutive readings without having to skip any data. | ||
#include < | #include < | ||
Line 262: | Line 170: | ||
#define ITG3200_TEMP_OFFSET 35 | #define ITG3200_TEMP_OFFSET 35 | ||
#define ITG3200_ROT_RAW_SENSITIVITY 14.375 | #define ITG3200_ROT_RAW_SENSITIVITY 14.375 | ||
- | + | ||
- | void read_itg3200 | + | int twosc2int(int twoscomplimentdata) |
+ | { int retval; | ||
+ | if( twoscomplimentdata > 32768 ) retval = twoscomplimentdata - 65536; | ||
+ | else retval = twoscomplimentdata; | ||
+ | return retval; | ||
+ | } | ||
+ | |||
+ | float ITG3200_rot_conv(int rawdata) | ||
+ | { float retval; | ||
+ | int raw; | ||
+ | |||
+ | raw=twosc2int(rawdata); | ||
+ | retval = (float)raw / (float)ITG3200_ROT_RAW_SENSITIVITY; | ||
+ | return retval; | ||
+ | } | ||
+ | |||
+ | float ITG3200_temp_conv(int rawdata) | ||
+ | { float retval; | ||
+ | int raw; | ||
+ | |||
+ | raw=twosc2int(rawdata); | ||
+ | retval = (float)ITG3200_TEMP_OFFSET + (((float)raw + ITG3200_TEMP_RAW_OFFSET) / ITG3200_TEMP_RAW_SENSITIVITY); | ||
+ | return retval; | ||
+ | } | ||
+ | | ||
+ | void ITG3200_read | ||
{ __s32 res; | { __s32 res; | ||
int i,j,k; | int i,j,k; | ||
Line 269: | Line 202: | ||
for(i=0; | for(i=0; | ||
{ k=0; | { k=0; | ||
- | printf(" | ||
for (j=0; | for (j=0; | ||
{ | { | ||
Line 279: | Line 211: | ||
else | else | ||
{ k += (int)res; | { k += (int)res; | ||
- | | + | *(raw + (i/2))=k; |
- | | + | |
} | } | ||
} | } | ||
Line 288: | Line 219: | ||
| | ||
main () | main () | ||
- | { int file,buffer; | + | { int file; |
int i,j,k; | int i,j,k; | ||
- | float data[4], | + | float data[4]={0}; |
- | char buf[256] = {0}; | + | |
| | ||
int ITG3200_REGS[8]={ITG3200_TH, | int ITG3200_REGS[8]={ITG3200_TH, | ||
Line 308: | Line 238: | ||
} | } | ||
| | ||
+ | /*Take an avarage over 10 consecuitve readings on the ITG3200*/ | ||
for (i=0; | for (i=0; | ||
- | { read_itg3200(file,& | + | { ITG3200_read(file,& |
- | printf(" | + | |
- | } | + | |
| | ||
- | for (i=0; | + | data[0] += ITG3200_temp_conv(ITG3200_RAW_DATA[0]); |
- | { printf("%2x ",ITG3200_RAW_DATA[i]); | + | data[1] += ITG3200_rot_conv(ITG3200_RAW_DATA[1]); |
+ | data[2] | ||
+ | | ||
} | } | ||
- | printf(" | + | |
+ | |||
+ | printf(" | ||
+ | printf(" | ||
+ | printf(" | ||
+ | | ||
+ | | ||
close(file); | close(file); | ||
} | } | ||
+ | |||
====== Voltage Level Shifting ====== | ====== Voltage Level Shifting ====== | ||
You may end up with heterogeneous voltage level devices and if you have many devices the correct way to work around this problem is by using bidirectional I2C voltage level shifters like the [[ http:// | You may end up with heterogeneous voltage level devices and if you have many devices the correct way to work around this problem is by using bidirectional I2C voltage level shifters like the [[ http:// | ||
- | This is how I connected my 5v IMU pcb to a 3.3v I2C bus on my RaspberryPI: | + | This is how I connected my 5v IMU pcb to a 3.3v I2C bus on my RaspberryPI: |
+ | ====== Hacking I2C in DIMM modules ====== | ||
+ | A | ||
====== Sources ====== | ====== Sources ====== | ||
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