I2C with HiPi::BCM2835::I2C
Part of the HiPi::BCM2835 distribution.
Class Methods
HiPi::BCM2835::I2C->get_baudrate($channel);
Returns the current baudrate of the BSC peripheral in $channel.
$channel can be one of BB_I2C_PERI_0 or BB_I2C_PERI_1.
On all Raspberry Pi models other than Model B Revsion 1 boards,
BB_I2C_PERI_1 is broken out on Raspberry Pins 3 and 5. For Model
B Revsion 1 boards alone, BB_I2C_PERI_0 is broken out on these pins.
Please note that the object method $obj->get_baudrate returns the
baudrate that will be used in transfers using that particular
instance of HiPi::BCM2835::I2C. You may be able to apply different
bus speeds to different devices using individual instance
settings.
HiPi::BCM2835::I2C->set_baudrate( $baudrate, $channel );
Sets the baudrate of the BSC peripheral in $channel.
$channel can be one of BB_I2C_PERI_0 or BB_I2C_PERI_1.
On all Raspberry Pi models other than Model B Revsion 1 boards,
BB_I2C_PERI_1 is broken out on Raspberry Pins 3 and 5. For Model
B Revsion 1 boards alone, BB_I2C_PERI_0 is broken out on these pins.
Common values for baudrate are:
3816 - the minimum supported
100000 - the i2c standard
400000 - fast i2c standard
1000000 - seems to be the fastest reliable speed that this
implementation supports. Of course, all the
devices on your bus must support this too.
32000 - the Broadcom I2C peripherals don't support
clock stretching so if you have a device that
employs this, a baudrate of 32000 ( or perhaps
even lower ) will often allow the device to work.
Please note that the object method $obj->set_baudrate($newrate) sets
the baudrate that will be used in transfers using that particular
instance of HiPi::BCM2835::I2C. You may be able to apply different
bus speeds to different devices using individual instance
settings.
Exported Constants
use HiPi::BCM2835 qw( :i2c );
exports:
BB_I2C_PERI_0
BB_I2C_PERI_1
BB_I2C_RESULT_SUCCESS
BB_I2C_RESULT_NACKRCV
BB_I2C_RESULT_CLOCKTO
BB_I2C_RESULT_DATAERR
Object Constructor and Methods
my $dev = HiPi::BCM2835::I2C->new( address => $devaddress );
$devaddress address of the device ( e.g. 0x20 ) on the
default perpheral. The default perpheral is determined according
to your Pi board revision.
Model B revision 1 = BB_I2C_PERI_0
All other boards = BB_I2C_PERI_1
Returns a new instance of the HiPi::BCM2835::I2C class.
You can specify which i2c channel to use in the constructor if
you wish using the key 'peripheral'.
my $dev = HiPi::BCM2835::I2C->new(
peripheral => BB_I2C_PERI_1,
address => 0x28
);
For interface modules that use I2C, you may specify
backend => 'bcm2835'
in the constructor to use this module as a backend.
HiPi::BCM2835::I2C supports 3 different read modes:
use HiPi::Constant qw( :i2c_readmode );
# default
my $dev = HiPi::BCM2835::I2C->new(
address => 0x28,
readmode => I2C_READMODE_SYSTEM,
);
The default and 2 other options:
I2C_READMODE_START_STOP
I2C_READMODE_REPEATED_START
are discussed in I2C Repeated Start
$dev->get_baudrate();
Returns the baudrate that will be used in transfers using this
particular instance of HiPi::BCM2835::I2C. You may be able to apply
different bus speeds to different devices using individual instance
settings.
$dev->set_baudrate( $baudrate );
Sets the baudrate that will be used in transfers using this
particular instance of HiPi::BCM2835::I2C. You may be able to apply
different bus speeds to different devices using individual instance
settings for baudrate.
Common values for baudrate are:
3816 - the minimum supported
100000 - the i2c standard
400000 - fast i2c standard
1000000 - seems to be the fastest reliable speed that this
implementation supports. Of course, all the
devices on your bus must support this too.
32000 - the Broadcom I2C peripherals don't support
clock stretching so if you have a device that
employs this, a baudrate of 32000 ( or perhaps
even lower ) will often allow the device to work.
Busmode Methods
HiPi::BCM2835::I2C provides wrappers for its i2c calls. Note that HiPi::Device::I2C also supports these methods so you may write code that works with backends i2c, smbus and bcm2835.
The bus methods implement support for the readmode settings ( I2C_READMODE_SYSTEM, I2C_READMODE_START_STOP, I2C_READMODE_REPEATED_START ). Specifically the method bus_read has its behaviour altered by the readmode constants.
See : I2C Repeated Start
$dev->bus_write( @params );
The module provides the method bus_write as
a generic call to the current backend.
@params is a list of bytes to write to the currently
addressed device.
$dev->bus_write_error( @params );
The module provides the method bus_write_error as
a generic call to the current backend.
@params is a list of bytes to write to the currently
addressed device.
The bus_write_error method is error tolerant and is
generally used when an external device has a soft reset
or reboot call that exits the i2c conversation when 'reset'
is set. The standard i2c_write command will return an
error in this case as the slave did not acknowledge the
reset byte.
$dev->bus_read( $cmdval, $numbytes );
The module provides the method bus_read as
a generic call to the current backend.
$cmdval is the value ( normally a register address
on the slave) that you wish to read from.
$numbytes is the number of bytes you wish to read.
Returns an array of bytes $numbytes long.
$dev->bus_read_bits( $cmdval, $numbytes );
The module provides the method bus_read_bits as
a generic call to the current backend.
Returns an array of bits 8 * $numbytes long from the
register in $cmdval.
If a single byte is read that has the value 0b01001100
then the bits in the array will have the values:
$return[7] == 0
$return[6] == 1
$return[5] == 0
$return[4] == 0
$return[3] == 1
$return[2] == 1
$return[1] == 0
$return[0] == 0
Usage:
my @bits = $dev->bus_read_bits(0xC1, 1);
$bits[3] = 1;
dev->bus_write_bits(0xC1, @bits);
$dev->bus_write_bits( $cmdval, @bits );
The module provides the method bus_write_bits as
a generic call to the current backend.
Writes a number of bytes equal to @bits / 8 to the
register in $cmdval.
For the array of 8 bits:
my @bits = ( 1,1,1,0,0,0,0,1 )
the value 0b10000111 will be written to $cmdval.
Usage:
my @bits = $dev->bus_read_bits(0xC1, 1);
$bits[3] = 1;
dev->bus_write_bits(0xC1, @bits);
I2C Methods
$dev->i2c_write( @params );
@params is a list of bytes to write to the slave device.
Normally, the first (and perhaps only) item in the list will
be a register address on the slave.
Use of the busmode wrapper methods is recommended.
$dev->i2c_write_error( @params );
@params is a list of bytes to write to the slave device.
Normally, the first (and perhaps only) item in the list will
be a register address on the slave.
The i2c_write_error method is error tolerant and is generally
used when an external device has a soft reset or reboot call
that exits the i2c conversation when 'reset' is set.
The standard i2c_write command will return an error in this case
as the slave did not acknowledge the reset byte.
$dev->i2c_read( $numbytes );
Reads a number of bytes $numbytes read from the current
register address in the slave (normally set using a previous
write).
Returns an array of bytes containing $numbytes items.
Use of the busmode wrapper methods is recommended.
$dev->i2c_read_register( $register, $numbytes );
Reads a number of bytes $numbytes read from the register
address in $register.
Combines the write of the register address with the subsequent
read in a single transaction.
Returns an array of bytes containing $numbytes items.
Use of the busmode wrapper methods is recommended.
$dev->i2c_read_register_rs( $register, $numbytes );
Reads a number of bytes $numbytes read from the register
address in $register.
Combines the write of the register address with the subsequent
read in a single transaction.
Returns an array of bytes containing $numbytes items.
This method is designed for slaves that require sending a
repeated start before a read can commence. It is used in place
of i2c_read_register for such devices.
HiPi::Interface::MPL3115A2 which provides access to a popular
temperature and pressure sensor requires this method.
Timing Methods
$dev->delay( $millis );
$millis Delay in milliseconds
Delays for the specified number of milliseconds. Uses nanosleep(),
and therefore does not use CPU until the time is up. However, you are
at the mercy of nanosleep(). From the manual for nanosleep(): If the
interval specified in req is not an exact multiple of the granularity
underlying clock (see time(7)), then the interval will be rounded up
to the next multiple. Furthermore, after the sleep completes, there
may still be a delay before the CPU becomes free to once again execute
the calling thread.
$dev->delayMicroseconds( $micros );
$micros Delay in microseconds
Delays for the specified number of microseconds. Uses a combination of
nanosleep() and a busy wait loop on the BCM2835 system timers, However,
you are at the mercy of nanosleep(). From the manual for nanosleep():
If the interval specified in req is not an exact multiple of the
granularity underlying clock (see time(7)), then the interval will be
rounded up to the next multiple. Furthermore, after the sleep completes,
there may still be a delay before the CPU becomes free to once again
execute the calling thread. For times less than about 450 microseconds,
uses a busy wait on the System Timer. It is reported that a delay of 0
microseconds on RaspberryPi will in fact result in a delay of about
80 microseconds. Your mileage may vary.