Nios® V Processor Software Developer Handbook

ID 743810
Date 10/31/2022
Public

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Document Table of Contents

7.7.1.1. Create a Device Instance

For a device to be made available as a character mode device, it must provide an instance of the alt_dev structure. The alt_dev structure, defined in <Intel Quartus Prime installation directory>/ip/altera/soft_processor/altera_hal2/HAL/inc/sys/alt_dev.h , is essentially a collection of function pointers. These functions are called in response to application accesses to the HAL file system. For example, if you call the function open() with a file name that corresponds to this device, the result is a call to the open() function provided in this structure.

alt_dev Structure

typedef struct 
{
   alt_llist llist; /* for internal use */
   const char* name; 
   int (*open) (alt_fd* fd, const char* name, int flags, int mode);
   int (*close) (alt_fd* fd);
   int (*read) (alt_fd* fd, char* ptr, int len);
   int (*write) (alt_fd* fd, const char* ptr, int len); 
   int (*lseek) (alt_fd* fd, int ptr, int dir);
   int (*fstat) (alt_fd* fd, struct stat* buf);
   int (*ioctl) (alt_fd* fd, int req, void* arg);
} 
alt_dev;

For more information about open(), close(), read(), write(), lseek(), fstat(), and ioctl(), refer to the HAL API Reference section.