hpet_example - HPET sample Application の履歴(No.12)

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hpet_example†

HPET (High Precision Event Timer) ドライバ /drivers/char/hpet.c の動作を理解するために、実際に動かすアプリケーション・プログラム hpet_example.tar.gz を使います。このプログラムは /Documentation/timers/hpet_example.c を修正して作成してあります。/Documentation/timers/hpet.txt で hpet_example.c について概要が書かれています。情報量は多く有りません。ioctl() API の仕様詳細は書かれていません。

ioctl API†

HPET driver's API†

Interrupt On - HPET_IE_ON†

• SYNOPSIS

  int ioctl(int fd, HPET_IE_ON);
  

• PRECONDITION
  
  • Set interrupt frequency by HPET_IRQFREQ.
  • Enable or disable hardware implemented periodic interrupt by HPET_EPI or HPET_DPI.
• DESCRIPTION
  Enable timer interrupt assigned to file descriptor fd. When the timer interrupts a processor, file descriptor fd becomes ready with event (POLLIN | POLLRDNORM) and also raise signal if a process sets file status flag O_ASYNC, valid owner, and signal number to fd.
• RETURN VALUE
  • 0: Success
  • -1: Error
• ERRORS
  • EBADF: Invalid file descriptor fd.
  • EIO: It occurs one of following conditions.
    • Invalid interrupt frequency.
    • Interrupt frequency has not been set.
    • Can't request IRQ handler. It may chipset or BIOS bug.
  • EBUSY
    • Already enabled interrupt.
• KERNEL SOURCE
  HPET_IE_ON, , hpet_interrupt()

Interrupt Off - HPET_IE_OFF†

• SYNOPSIS

  int ioctl(int fd, HPET_IE_OFF);
  

• DESCRIPTION
  Disable timer interrupt assigned to file descriptor fd.
• RETURN VALUE
  • 0: Success
  • -1: Error
• ERRORS
  • EBADF: Invalid file descriptor fd.
• KERNEL SOURCE
  HPET_IE_OFF

Get Information - HPET_INFO†

• SYNOPSIS

  struct hpet_info {
  	unsigned long  hi_ireqfreq; /* Period or time in Hz */
  	unsigned long  hi_flags;    /* Information: 0x0: Not supported periodic int., 0x10: Supported periodic int. */
  	unsigned short hi_hpet;     /* HPET device number, [0..TheNumberOfHPETDevicesInPlatform-1] */
  	unsigned short hi_timer;    /* Timer number in HPET device, [0..31] */
  };
  int ioctl(int fd, HPET_INFO, /* out */ struct hpet_info *info);
  

• DESCRIPTION
  Get timer information assigned to file descriptor fd. ioctl call with HPET_INFO stores timer information to *info. This ioctl call fills hpet_info members as follows.

  member	description
  hi_ireqfreq	Interrupt frequency in Hz.
  hi_flags	Timer capability. The value will be as follows, 0x00UL This timer doesn't have hardware implemented periodic interrupt. 0x10UL This timer has hardware implemented periodic interrupt.
  hi_hpet	HPET device number on platform. It satisfies (hi_hpet >= 0) && (hi_hpet < M), where M is the number of HPET devices (circuit blocks) on platform.
  hi_timer	Timer number in HPET device. It satisfies (hi_timer >= 0) && (hi_timer < N), where N is the number of timers in HPET device and N <= 32. NOTE: You may see {hi_hpet, hi_timer} == {0, 2} at first opened HPET timer, because the timer 0 and timer 1 replaces PIT(programmable Interval Timer) and RTC(Real Time Clock).

• RETURN VALUE
  • 0: Success
  • -1: Error
• ERRORS
  • EBADF: Invalid file descriptor fd.
  • EFAULT: info points an inaccessible memory area.
• KERNEL SOURCE
  HPET_INFO

Enable hardware periodic interrupt - HPET_EPI†

• SYNOPSIS

  int ioctl(int fd, HPET_EPI);
  

• PRECONDITION
  
  • Disabling timer interrupt, HPET_IE_OFF.
• DESCRIPTION
  Enable hardware implemented periodic interrupt at timer assigned to file descriptor fd, and disable software assisted periodic interrupt. Call HPET_EPI ioctl() before enabling timer interrupt HPET_IE_ON.
• RETURN VALUE
  
  • 0: Success
  • -1: Error
• ERRORS
  • EBADF: Invalid file descriptor fd.
  • ENXIO: The timer's hardware assigned to file descriptor fd doesn't support periodic interrupt.
• KERNEL SOURCE
  HPET_EPI

Disable hardware periodic interrupt - HPET_DPI†

• SYNOPSIS

  int ioctl(int fd, HPET_DPI);
  

• PRECONDITION
  
  • Disabling timer interrupt, HPET_IE_OFF.
• DESCRIPTION
  Disable hardware implemented periodic interrupt at timer assigned to file descriptor fd, and enable software assisted periodic interrupt. Call HPET_DPI ioctl() before enabling timer interrupt HPET_IE_ON.
  When using HPET timer with HPET_DPI (disabling hardware periodic interrupt), HPET driver updates interrupt time in interrupt handler. So timer interrupts periodically and interrupt period includes software response time delay.
• RETURN VALUE
  
  • 0: Success
  • -1: Error
• ERRORS
  • EBADF: Invalid file descriptor fd.
  • ENXIO: The timer's hardware assigned to file descriptor fd doesn't support periodic interrupt.
• KERNEL SOURCE
  HPET_DPI, hpet_interrupt()

Set Interrupt Frequency in Hz - HPET_IRQFREQ†

• SYNOPSIS

  int ioctl(int fd, HPET_IRQFREQ, unsigned long frequency);
  

• PRECONDITION
  
  • Disabling timer interrupt, HPET_IE_OFF.
• DESCRIPTION
  Set interrupt frequency to timer assigned to file descriptor fd. Specify frequency in Hz. If process hasn't CAP_SYS_RESOURCE capability, frequency is limited less or equal to the value read from /proc/sys/dev/hpet/max-user-freq. The default value read from max-user-freq is 64 (==HPET_USER_FREQ).
  Don't update frequency while enabling interrupt.
• RETURN
  
  • 0: Success
  • -1: Error
• ERRORS
  • EACCESS Process doesn't have capability CAP_SYS_RESOURCE and try to set frequency more than the value read from /proc/sys/dev/hpet/max-user-freq. The default value read from max-user-freq is 64 (==HPET_USER_FREQ).
  • EINVAL: Frequency is zero.
• KERNEL SOURCE
  HPET_IRQFREQ, hpet_max_freq, HPET_USER_FREQ, hpet_interrupt()

File System API related to HPET†

To see more details refer to man 2 fcntl.

open HPET timer†

• SYNOPSIS

  int open(const char *hpet_path, O_RDONLY);
  

• DESCRIPTION
  

close HPET timer†

int close(int fd);

• DESCRIPTION
  

F_GETOWN†

• SYNOPSIS

  int fcntl(int fd, F_GETOWN);
  

• DESCRIPTION
  Get owner assigned to file descriptor fd.
• RETURN VALUE
  
  • 0: no owner, it doesn't raise signal.
  • return_value > 0: process id number.
  • return_value < 0: Negative process group number. Be careful, it may treated as an error. It is better to use F_GETOWN_EX.
• KERNEL SOURCE
  F_GETOWN

F_GETOWN_EX†

• SYNOPSIS

  struct f_owner_ex {
    int    type; /* F_OWNER_PID, F_OWNER_PGRP, or     F_OWNER_TID */
    pid_t  pid;  /* process id,  process group id, or thread id. */
  }
  int fcntl(int fd, F_GETOWN_EX, /* out */ struct f_owner_ex *owner_ex);
  

• DESCRIPTION
  Get owner assigned to file descriptor fd. fcntl() F_GETOWN_EX call stores result in *owner_ex. See more details in F_SETOWN_EX.
• KERNEL SOURCE
  F_GETOWN_EX

F_SETOWN†

• SYNOPSIS

  int fcntl(int fd, F_SETOWN, int owner);
  

• DESCRIPTION
  Set owner to file descriptor fd. owner is process id, or negative process group id. When the timer assigned to fd interrupts a processor and the fd's file status flags has been ORed with O_ASYNC, a signal is sent to owner.
• KERNEL SOURCE
  F_SETOWN

F_SETOWN_EX†

• SYNOPSIS

  struct f_owner_ex {
    int    type; /* F_OWNER_PID, F_OWNER_PGRP, or     F_OWNER_TID */
    pid_t  pid;  /* process id,  process group id, or thread id. */
  }
  int fcntl(int fd, F_GETOWN_EX, /* in */ struct f_owner_ex *owner_ex);
  

• DESCRIPTION
  Set one of process id, process group id, or thread id to file descriptor fd. type specifies pid containing which id. type should be one of F_OWNER_PID (process id), F_OWNER_PGRP (process group id), or F_OWNER_TID (thread id), and set process, process group, or thread id to pid.
  When the timer assigned to fd interrupts a processor and the fd's file status flags has been ORed with O_ASYNC, a signal is sent to pid.
• KERNEL SOURCE
  F_SETOWN_EX

F_GETFL†

• SYNOPSIS

  int fcntl(int fd, F_GETFL);
  

• DESCRIPTION
  Use this function to set or clear O_ASYNC flag to file descriptor fd. See the description of F_SETFL.
• KERNEL SOURCE
  F_GETFL

F_SETFL†

• SYNOPSIS

  int fcntl(int fd, F_SETFL, int flags);
  

• DESCRIPTION
  To raise signal on timer interrupt, let flags be ORed with O_ASYNC, see following pseudo code piece.
  

  1 2 3 4 5 6 7 8 9 10

  - | - | ! | - | ! !

  { int flags; flags = fcntl(fd, F_GETFL); if (flags < 0) { /* error handling. */ } flags |= O_ASYNC; if (fcntl(fd, F_SETFL, flags) != 0) { /* error handling. */ } }

• KERNEL SOURCE
  F_SETFL, setfl(), #define O_ASYNC FASYNC

F_GETSIG†

• SYNOPSIS

  int fcntl(int fd, F_GETSIG);
  

• DESCRIPTION
  Get the signal number will be raised on timer interrupt.
• KERNEL SOURCE
  F_GETSIG

F_SETSIG†

• SYNOPSIS

  int fcntl(int fd, F_SETSIG, int signal);
  

• DESCRIPTION
  Set the signal number will be raised on timer interrupt.
• KERNEL SOURCE
  F_SETSIG, send_sigio()