Embedded Files
The MCP23017SP is a I2C Bus expander featuring two 8-bit programmable ports, I picked this chip because of already existing support and using the I2C port seemed to be the easiest way to add the ports I need for a few projects I was looking at starting.
This is my first project for the Beaglebone black, pushing buttons and turning on LED's I done on so many other boards. With the higher cost of the beaglebone over some of the other boards I use. Using an external board with I2C help protect from blowing out any pins on the Beaglebone or the board itself. With the Bus expander chips only a couple of dollars, blowing one of them is not as big a deal as $30+ dollar board. Also the expander chips allows me to access 5 volt logic levels that I can not do with the beagledone.
My first step was learning how to read and write to the I2C bus, here is my simple library with the Z-80 bus control program to load programs. The Library is based around the Linux i2c_smbus system calls to access the i2c buss. Note on the to-do list better error handling
Below is example of the MCP23017 being used as a Host interface to my Z-80 system
List of basic i2c calls used by library, which could be the core of writing/read from any i2c device.
int Open_i2c_bus(int i2c_bus);
__u8 Read_i2c_port( int file, __u8 chip_add, __u8 chip_reg);
__u8 Read_i2c_port_bit (int file, __u8 chip_add, __u8 chip_reg, char bit);
__u8 Write_i2c_port( int file, __u8 chip_add, __u8 chip_reg, __u8 data);
__u8 Write_i2c_port_bit( int file, __u8 chip_add, __u8 chip_reg, __u8 bit, char set_bit);
Below is core files for access of the i2c bus
Notes: Beaglebone Black open I2C port is 1.
/* i2c utiility library 2015 */
/* eric.stringer@gmail.com */
#include <sys/ioctl.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include "i2c-dev.h"
#include "i2c_util.h"
unsigned char Bit_mask[8] = {0b00000001, 0b00000010, 0b00000100, 0b00001000, 0b00010000, 0b00100000, 0b01000000, 0b10000000};
int Open_i2c_bus(int i2c_bus)
{
int file;
char filename[20];
snprintf(filename, 19, "/dev/i2c-%d", i2c_bus);
file = open(filename, O_RDWR);
if (file < 0) {
printf("Could not open I2C \n");/* ERROR HANDLING; you can check errno to see what went wrong */
exit(1);
}else{
printf("Opened I2C bus \n");
}
return( file );
}
__u8 Read_i2c_port( int file, __u8 chip_add, __u8 chip_reg)
{
__u8 data;
if (ioctl(file, I2C_SLAVE, chip_add) < 0) {
printf("Failed to acquire bus access and/or talk to slave.\n");
/* ERROR HANDLING; you can check errno to see what went wrong */
exit(1);
}
data = i2c_smbus_read_byte_data(file, chip_reg);
return( data );
}
__u8 Write_i2c_port( int file, __u8 chip_add, __u8 chip_reg, __u8 data)
{
if (ioctl(file, I2C_SLAVE, chip_add) < 0) {
printf("Failed to acquire bus access and/or talk to slave.\n");
/* ERROR HANDLING; you can check errno to see what went wrong */
exit(1);
}
i2c_smbus_write_byte_data(file, chip_reg, data);
}
__u8 Read_i2c_port_bit (int file, __u8 chip_add, __u8 chip_reg, char bit)
{
__u8 data;
if (ioctl(file, I2C_SLAVE, chip_add) < 0) {
printf("Failed to acquire bus access and/or talk to slave.\n");
/* ERROR HANDLING; you can check errno to see what went wrong */
exit(1);
}
if (bit > 7 ) bit = 7;
data = i2c_smbus_read_byte_data(file, chip_reg) & Bit_mask[bit];
if (data != 0) data = 1;
return(data);
}
__u8 Write_i2c_port_bit( int file, __u8 chip_add, __u8 chip_reg, __u8 bit, char set_bit)
{
__u8 data;
if (ioctl(file, I2C_SLAVE, chip_add) < 0) {
printf("Failed to acquire bus access and/or talk to slave.\n");
/* ERROR HANDLING; you can check errno to see what went wrong */
exit(1);
}
if (bit > 7) bit = 7;
if (set_bit == 0)
{
data = i2c_smbus_read_byte_data(file, chip_reg) & ~Bit_mask[bit];
i2c_smbus_write_byte_data(file, chip_reg, data);
}else{
data = i2c_smbus_read_byte_data(file, chip_reg) | Bit_mask[bit];
i2c_smbus_write_byte_data(file, chip_reg, data);
}
}
/* i2c_util.h */
int Open_i2c_bus(int i2c_bus);
__u8 Read_i2c_port( int file, __u8 chip_add, __u8 chip_reg);
__u8 Read_i2c_port_bit (int file, __u8 chip_add, __u8 chip_reg, char bit);
__u8 Write_i2c_port( int file, __u8 chip_add, __u8 chip_reg, __u8 data);
__u8 Write_i2c_port_bit( int file, __u8 chip_add, __u8 chip_reg, __u8 bit, char set_bit);
#ifndef _LINUX_I2C_DEV_H
#define _LINUX_I2C_DEV_H
#include <linux/types.h>
#include <sys/ioctl.h>
#include <stddef.h>
/* -- i2c.h -- */
/*
* I2C Message - used for pure i2c transaction, also from /dev interface
*/
struct i2c_msg {
__u16 addr; /* slave address */
unsigned short flags;
#define I2C_M_TEN 0x10 /* we have a ten bit chip address */
#define I2C_M_RD 0x01
#define I2C_M_NOSTART 0x4000
#define I2C_M_REV_DIR_ADDR 0x2000
#define I2C_M_IGNORE_NAK 0x1000
#define I2C_M_NO_RD_ACK 0x0800
short len; /* msg length */
char *buf; /* pointer to msg data */
};
/* To determine what functionality is present */
#define I2C_FUNC_I2C 0x00000001
#define I2C_FUNC_10BIT_ADDR 0x00000002
#define I2C_FUNC_PROTOCOL_MANGLING 0x00000004 /* I2C_M_{REV_DIR_ADDR,NOSTART,..} */
#define I2C_FUNC_SMBUS_PEC 0x00000008
#define I2C_FUNC_SMBUS_BLOCK_PROC_CALL 0x00008000 /* SMBus 2.0 */
#define I2C_FUNC_SMBUS_QUICK 0x00010000
#define I2C_FUNC_SMBUS_READ_BYTE 0x00020000
#define I2C_FUNC_SMBUS_WRITE_BYTE 0x00040000
#define I2C_FUNC_SMBUS_READ_BYTE_DATA 0x00080000
#define I2C_FUNC_SMBUS_WRITE_BYTE_DATA 0x00100000
#define I2C_FUNC_SMBUS_READ_WORD_DATA 0x00200000
#define I2C_FUNC_SMBUS_WRITE_WORD_DATA 0x00400000
#define I2C_FUNC_SMBUS_PROC_CALL 0x00800000
#define I2C_FUNC_SMBUS_READ_BLOCK_DATA 0x01000000
#define I2C_FUNC_SMBUS_WRITE_BLOCK_DATA 0x02000000
#define I2C_FUNC_SMBUS_READ_I2C_BLOCK 0x04000000 /* I2C-like block xfer */
#define I2C_FUNC_SMBUS_WRITE_I2C_BLOCK 0x08000000 /* w/ 1-byte reg. addr. */
#define I2C_FUNC_SMBUS_BYTE (I2C_FUNC_SMBUS_READ_BYTE | \
I2C_FUNC_SMBUS_WRITE_BYTE)
#define I2C_FUNC_SMBUS_BYTE_DATA (I2C_FUNC_SMBUS_READ_BYTE_DATA | \
I2C_FUNC_SMBUS_WRITE_BYTE_DATA)
#define I2C_FUNC_SMBUS_WORD_DATA (I2C_FUNC_SMBUS_READ_WORD_DATA | \
I2C_FUNC_SMBUS_WRITE_WORD_DATA)
#define I2C_FUNC_SMBUS_BLOCK_DATA (I2C_FUNC_SMBUS_READ_BLOCK_DATA | \
I2C_FUNC_SMBUS_WRITE_BLOCK_DATA)
#define I2C_FUNC_SMBUS_I2C_BLOCK (I2C_FUNC_SMBUS_READ_I2C_BLOCK | \
I2C_FUNC_SMBUS_WRITE_I2C_BLOCK)
/* Old name, for compatibility */
#define I2C_FUNC_SMBUS_HWPEC_CALC I2C_FUNC_SMBUS_PEC
/*
* Data for SMBus Messages
*/
#define I2C_SMBUS_BLOCK_MAX 32 /* As specified in SMBus standard */
#define I2C_SMBUS_I2C_BLOCK_MAX 32 /* Not specified but we use same structure */
union i2c_smbus_data {
__u8 byte;
__u16 word;
__u8 block[I2C_SMBUS_BLOCK_MAX + 2]; /* block[0] is used for length */
/* and one more for PEC */
};
/* smbus_access read or write markers */
#define I2C_SMBUS_READ 1
#define I2C_SMBUS_WRITE 0
/* SMBus transaction types (size parameter in the above functions)
Note: these no longer correspond to the (arbitrary) PIIX4 internal codes! */
#define I2C_SMBUS_QUICK 0
#define I2C_SMBUS_BYTE 1
#define I2C_SMBUS_BYTE_DATA 2
#define I2C_SMBUS_WORD_DATA 3
#define I2C_SMBUS_PROC_CALL 4
#define I2C_SMBUS_BLOCK_DATA 5
#define I2C_SMBUS_I2C_BLOCK_BROKEN 6
#define I2C_SMBUS_BLOCK_PROC_CALL 7 /* SMBus 2.0 */
#define I2C_SMBUS_I2C_BLOCK_DATA 8
/* /dev/i2c-X ioctl commands. The ioctl's parameter is always an
* unsigned long, except for:
* - I2C_FUNCS, takes pointer to an unsigned long
* - I2C_RDWR, takes pointer to struct i2c_rdwr_ioctl_data
* - I2C_SMBUS, takes pointer to struct i2c_smbus_ioctl_data
*/
#define I2C_RETRIES 0x0701 /* number of times a device address should
be polled when not acknowledging */
#define I2C_TIMEOUT 0x0702 /* set timeout in units of 10 ms */
/* NOTE: Slave address is 7 or 10 bits, but 10-bit addresses
* are NOT supported! (due to code brokenness)
*/
#define I2C_SLAVE 0x0703 /* Use this slave address */
#define I2C_SLAVE_FORCE 0x0706 /* Use this slave address, even if it
is already in use by a driver! */
#define I2C_TENBIT 0x0704 /* 0 for 7 bit addrs, != 0 for 10 bit */
#define I2C_FUNCS 0x0705 /* Get the adapter functionality mask */
#define I2C_RDWR 0x0707 /* Combined R/W transfer (one STOP only) */
#define I2C_PEC 0x0708 /* != 0 to use PEC with SMBus */
#define I2C_SMBUS 0x0720 /* SMBus transfer */
/* This is the structure as used in the I2C_SMBUS ioctl call */
struct i2c_smbus_ioctl_data {
__u8 read_write;
__u8 command;
__u32 size;
union i2c_smbus_data *data;
};
/* This is the structure as used in the I2C_RDWR ioctl call */
struct i2c_rdwr_ioctl_data {
struct i2c_msg *msgs; /* pointers to i2c_msgs */
__u32 nmsgs; /* number of i2c_msgs */
};
#define I2C_RDRW_IOCTL_MAX_MSGS 42
static inline __s32 i2c_smbus_access(int file, char read_write, __u8 command,
int size, union i2c_smbus_data *data)
{
struct i2c_smbus_ioctl_data args;
args.read_write = read_write;
args.command = command;
args.size = size;
args.data = data;
return ioctl(file,I2C_SMBUS,&args);
}
static inline __s32 i2c_smbus_write_quick(int file, __u8 value)
{
return i2c_smbus_access(file,value,0,I2C_SMBUS_QUICK,NULL);
}
static inline __s32 i2c_smbus_read_byte(int file)
{
union i2c_smbus_data data;
if (i2c_smbus_access(file,I2C_SMBUS_READ,0,I2C_SMBUS_BYTE,&data))
return -1;
else
return 0x0FF & data.byte;
}
static inline __s32 i2c_smbus_write_byte(int file, __u8 value)
{
return i2c_smbus_access(file,I2C_SMBUS_WRITE,value,
I2C_SMBUS_BYTE,NULL);
}
static inline __s32 i2c_smbus_read_byte_data(int file, __u8 command)
{
union i2c_smbus_data data;
if (i2c_smbus_access(file,I2C_SMBUS_READ,command,
I2C_SMBUS_BYTE_DATA,&data))
return -1;
else
return 0x0FF & data.byte;
}
static inline __s32 i2c_smbus_write_byte_data(int file, __u8 command,
__u8 value)
{
union i2c_smbus_data data;
data.byte = value;
return i2c_smbus_access(file,I2C_SMBUS_WRITE,command,
I2C_SMBUS_BYTE_DATA, &data);
}
static inline __s32 i2c_smbus_read_word_data(int file, __u8 command)
{
union i2c_smbus_data data;
if (i2c_smbus_access(file,I2C_SMBUS_READ,command,
I2C_SMBUS_WORD_DATA,&data))
return -1;
else
return 0x0FFFF & data.word;
}
static inline __s32 i2c_smbus_write_word_data(int file, __u8 command,
__u16 value)
{
union i2c_smbus_data data;
data.word = value;
return i2c_smbus_access(file,I2C_SMBUS_WRITE,command,
I2C_SMBUS_WORD_DATA, &data);
}
static inline __s32 i2c_smbus_process_call(int file, __u8 command, __u16 value)
{
union i2c_smbus_data data;
data.word = value;
if (i2c_smbus_access(file,I2C_SMBUS_WRITE,command,
I2C_SMBUS_PROC_CALL,&data))
return -1;
else
return 0x0FFFF & data.word;
}
/* Returns the number of read bytes */
static inline __s32 i2c_smbus_read_block_data(int file, __u8 command,
__u8 *values)
{
union i2c_smbus_data data;
int i;
if (i2c_smbus_access(file,I2C_SMBUS_READ,command,
I2C_SMBUS_BLOCK_DATA,&data))
return -1;
else {
for (i = 1; i <= data.block[0]; i++)
values[i-1] = data.block[i];
return data.block[0];
}
}
static inline __s32 i2c_smbus_write_block_data(int file, __u8 command,
__u8 length, const __u8 *values)
{
union i2c_smbus_data data;
int i;
if (length > 32)
length = 32;
for (i = 1; i <= length; i++)
data.block[i] = values[i-1];
data.block[0] = length;
return i2c_smbus_access(file,I2C_SMBUS_WRITE,command,
I2C_SMBUS_BLOCK_DATA, &data);
}
/* Returns the number of read bytes */
/* Until kernel 2.6.22, the length is hardcoded to 32 bytes. If you
ask for less than 32 bytes, your code will only work with kernels
2.6.23 and later. */
static inline __s32 i2c_smbus_read_i2c_block_data(int file, __u8 command,
__u8 length, __u8 *values)
{
union i2c_smbus_data data;
int i;
if (length > 32)
length = 32;
data.block[0] = length;
if (i2c_smbus_access(file,I2C_SMBUS_READ,command,
length == 32 ? I2C_SMBUS_I2C_BLOCK_BROKEN :
I2C_SMBUS_I2C_BLOCK_DATA,&data))
return -1;
else {
for (i = 1; i <= data.block[0]; i++)
values[i-1] = data.block[i];
return data.block[0];
}
}
static inline __s32 i2c_smbus_write_i2c_block_data(int file, __u8 command,
__u8 length,
const __u8 *values)
{
union i2c_smbus_data data;
int i;
if (length > 32)
length = 32;
for (i = 1; i <= length; i++)
data.block[i] = values[i-1];
data.block[0] = length;
return i2c_smbus_access(file,I2C_SMBUS_WRITE,command,
I2C_SMBUS_I2C_BLOCK_BROKEN, &data);
}
/* Returns the number of read bytes */
static inline __s32 i2c_smbus_block_process_call(int file, __u8 command,
__u8 length, __u8 *values)
{
union i2c_smbus_data data;
int i;
if (length > 32)
length = 32;
for (i = 1; i <= length; i++)
data.block[i] = values[i-1];
data.block[0] = length;
if (i2c_smbus_access(file,I2C_SMBUS_WRITE,command,
I2C_SMBUS_BLOCK_PROC_CALL,&data))
return -1;
else {
for (i = 1; i <= data.block[0]; i++)
values[i-1] = data.block[i];
return data.block[0];
}
}
#endif /* _LINUX_I2C_DEV_H */
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