NAME
<avr/lock.h>: Lockbit Support - Introduction
The Lockbit API allows a user to specify the lockbit settings for the
specific AVR device they are compiling for. These lockbit settings will
be placed in a special section in the ELF output file, after linking.
Programming tools can take advantage of the lockbit information
embedded in the ELF file, by extracting this information and
determining if the lockbits need to be programmed after programming the
Flash and EEPROM memories. This also allows a single ELF file to
contain all the information needed to program an AVR.
To use the Lockbit API, include the <avr/io.h> header file, which in
turn automatically includes the individual I/O header file and the
<avr/lock.h> file. These other two files provides everything necessary
to set the AVR lockbits.
Lockbit API
Each I/O header file may define up to 3 macros that controls what kinds
of lockbits are available to the user.
If __LOCK_BITS_EXIST is defined, then two lock bits are available to
the user and 3 mode settings are defined for these two bits.
If __BOOT_LOCK_BITS_0_EXIST is defined, then the two BLB0 lock bits are
available to the user and 4 mode settings are defined for these two
bits.
If __BOOT_LOCK_BITS_1_EXIST is defined, then the two BLB1 lock bits are
available to the user and 4 mode settings are defined for these two
bits.
If __BOOT_LOCK_APPLICATION_TABLE_BITS_EXIST is defined then two lock
bits are available to set the locking mode for the Application Table
Section (which is used in the XMEGA family).
If __BOOT_LOCK_APPLICATION_BITS_EXIST is defined then two lock bits are
available to set the locking mode for the Application Section (which is
used in the XMEGA family).
If __BOOT_LOCK_BOOT_BITS_EXIST is defined then two lock bits are
available to set the locking mode for the Boot Loader Section (which is
used in the XMEGA family).
The AVR lockbit modes have inverted values, logical 1 for an
unprogrammed (disabled) bit and logical 0 for a programmed (enabled)
bit. The defined macros for each individual lock bit represent this in
their definition by a bit-wise inversion of a mask. For example, the
LB_MODE_3 macro is defined as:
#define LB_MODE_3 (0xFC)
`
To combine the lockbit mode macros together to represent a whole byte,
use the bitwise AND operator, like so:
(LB_MODE_3 & BLB0_MODE_2)
<avr/lock.h> also defines a macro that provides a default lockbit
value: LOCKBITS_DEFAULT which is defined to be 0xFF.
See the AVR device specific datasheet for more details about these lock
bits and the available mode settings.
A convenience macro, LOCKMEM, is defined as a GCC attribute for a
custom-named section of '.lock'.
A convenience macro, LOCKBITS, is defined that declares a variable,
__lock, of type unsigned char with the attribute defined by LOCKMEM.
This variable allows the end user to easily set the lockbit data.
Note:
If a device-specific I/O header file has previously defined
LOCKMEM, then LOCKMEM is not redefined. If a device-specific I/O
header file has previously defined LOCKBITS, then LOCKBITS is not
redefined. LOCKBITS is currently known to be defined in the I/O
header files for the XMEGA devices.
API Usage Example
Putting all of this together is easy:
#include <avr/io.h>
LOCKBITS = (LB_MODE_1 & BLB0_MODE_3 & BLB1_MODE_4);
int main(void)
{
return 0;
}
Or:
#include <avr/io.h>
unsigned char __lock __attribute__((section ('.lock'))) =
(LB_MODE_1 & BLB0_MODE_3 & BLB1_MODE_4);
int main(void)
{
return 0;
}
However there are a number of caveats that you need to be aware of to
use this API properly.
Be sure to include <avr/io.h> to get all of the definitions for the
API. The LOCKBITS macro defines a global variable to store the lockbit
data. This variable is assigned to its own linker section. Assign the
desired lockbit values immediately in the variable initialization.
The .lock section in the ELF file will get its values from the initial
variable assignment ONLY. This means that you can NOT assign values to
this variable in functions and the new values will not be put into the
ELF .lock section.
The global variable is declared in the LOCKBITS macro has two leading
underscores, which means that it is reserved for the 'implementation',
meaning the library, so it will not conflict with a user-named
variable.
You must initialize the lockbit variable to some meaningful value, even
if it is the default value. This is because the lockbits default to a
logical 1, meaning unprogrammed. Normal uninitialized data defaults to
all locgial zeros. So it is vital that all lockbits are initialized,
even with default data. If they are not, then the lockbits may not
programmed to the desired settings and can possibly put your device
into an unrecoverable state.
Be sure to have the -mmcu=device flag in your compile command line and
your linker command line to have the correct device selected and to
have the correct I/O header file included when you include <avr/io.h>.
You can print out the contents of the .lock section in the ELF file by
using this command line:
avr-objdump -s -j .lock <ELF file>
Author
Generated automatically by Doxygen for avr-libc from the source code.
Version 1.6.8 Thu Aug 12 201<avr/lock.h>: Lockbit Support(3)