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• When the VALUE field is 0x0000, the mutex is unlocked and available. Otherwise, the mutex is locked

and unavailable.

• The mutex register is always readable. Avalon-MM master peripherals, such as a processor, can read

the mutex register to determine its current state.

• The mutex register is writable only under specific conditions. A write operation changes the mutex

• The VALUE field of the mutex register is zero.

• The OWNER field of the mutex register matches the OWNER field in the data to be written.

• A processor attempts to acquire the mutex by writing its ID to the OWNER field, and writing a non-zero

value to the VALUE field. The processor then checks if the acquisition succeeded by verifying the OWNER

field.

• After system reset, the RESET bit in the reset register is high. Writing a one to this bit clears it.

Configuration

The MegaWizard

™

Interface provides the following options:

• Initial Value—the initial contents of the VALUE field after reset. If the Initial Value setting is non-zero,

you must also specify Initial Owner.

• Initial Owner—the initial contents of the OWNER field after reset. When Initial Owner is specified, this

owner must release the mutex before it can be acquired by another owner.

Software Programming Model

The following sections describe the software programming model for the mutex core. For Nios II

processor users, Altera provides routines to access the mutex core hardware. These functions are specific

to the mutex core and directly manipulate low-level hardware. The mutex core cannot be accessed via the

HAL API or the ANSI C standard library. In Nios II processor systems, a processor locks the mutex by

writing the value of its cpuid control register to the OWNER field of the mutex register.

Software Files

Altera provides the following software files accompanying the mutex core:

• altera_avalon_mutex_regs.h—Defines the core's register map, providing symbolic constants to access the

low-level hardware.

• altera_avalon_mutex.h—Defines data structures and functions to access the mutex core hardware.

• altera_avalon_mutex.c—Contains the implementations of the functions to access the mutex core

Hardware Access Routines

This section describes the low-level software constructs for manipulating the mutex core. The file altera_

avalon_mutex.h declares a structure alt_mutex_dev that represents an instance of a mutex device. It also

declares routines for accessing the mutex hardware structure, listed in the table below.

Table 26-2: Hardware Access Routines

Function Name Description

altera_avalon_mutex_open() Claims a handle to a mutex, enabling all the other

functions to access the mutex core.

26-2

Configuration

UG-01085

2014.24.07

Altera Corporation

Mutex Core

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