199 строки
6.6 KiB
Plaintext
199 строки
6.6 KiB
Plaintext
README for MIPS time services
|
|
|
|
Jun Sun
|
|
jsun@mvista.com or jsun@junsun.net
|
|
|
|
|
|
ABOUT
|
|
-----
|
|
This file describes the new arch/mips/kernel/time.c, related files and the
|
|
services they provide.
|
|
|
|
If you are short in patience and just want to know how to use time.c for a
|
|
new board or convert an existing board, go to the last section.
|
|
|
|
|
|
FILES, COMPATABILITY AND CONFIGS
|
|
---------------------------------
|
|
|
|
The old arch/mips/kernel/time.c is renamed to old-time.c.
|
|
|
|
A new time.c is put there, together with include/asm-mips/time.h.
|
|
|
|
Two configs variables are introduced, CONFIG_OLD_TIME_C and CONFIG_NEW_TIME_C.
|
|
So we allow boards using
|
|
|
|
1) old time.c (CONFIG_OLD_TIME_C)
|
|
2) new time.c (CONFIG_NEW_TIME_C)
|
|
3) neither (their own private time.c)
|
|
|
|
However, it is expected every board will move to the new time.c in the near
|
|
future.
|
|
|
|
|
|
WHAT THE NEW CODE PROVIDES?
|
|
---------------------------
|
|
|
|
The new time code provide the following services:
|
|
|
|
a) Implements functions required by Linux common code:
|
|
time_init
|
|
do_gettimeofday
|
|
do_settimeofday
|
|
|
|
b) provides an abstraction of RTC and null RTC implementation as default.
|
|
extern unsigned long (*rtc_get_time)(void);
|
|
extern int (*rtc_set_time)(unsigned long);
|
|
|
|
c) a set of gettimeoffset functions for different CPUs and different
|
|
needs.
|
|
|
|
d) high-level and low-level timer interrupt routines where the timer
|
|
interrupt source may or may not be the CPU timer. The high-level
|
|
routine is dispatched through do_IRQ() while the low-level is
|
|
dispatched in assemably code (usually int-handler.S)
|
|
|
|
|
|
WHAT THE NEW CODE REQUIRES?
|
|
---------------------------
|
|
|
|
For the new code to work properly, each board implementation needs to supply
|
|
the following functions or values:
|
|
|
|
a) board_time_init - a function pointer. Invoked at the beginnig of
|
|
time_init(). It is optional.
|
|
1. (optional) set up RTC routines
|
|
2. (optional) calibrate and set the mips_counter_frequency
|
|
|
|
b) board_timer_setup - a function pointer. Invoked at the end of time_init()
|
|
1. (optional) over-ride any decisions made in time_init()
|
|
2. set up the irqaction for timer interrupt.
|
|
3. enable the timer interrupt
|
|
|
|
c) (optional) board-specific RTC routines.
|
|
|
|
d) (optional) mips_counter_frequency - It must be definied if the board
|
|
is using CPU counter for timer interrupt or it is using fixed rate
|
|
gettimeoffset().
|
|
|
|
|
|
PORTING GUIDE
|
|
-------------
|
|
|
|
Step 1: decide how you like to implement the time services.
|
|
|
|
a) does this board have a RTC? If yes, implement the two RTC funcs.
|
|
|
|
b) does the CPU have counter/compare registers?
|
|
|
|
If the answer is no, you need a timer to provide the timer interrupt
|
|
at 100 HZ speed.
|
|
|
|
You cannot use the fast gettimeoffset functions, i.e.,
|
|
|
|
unsigned long fixed_rate_gettimeoffset(void);
|
|
unsigned long calibrate_div32_gettimeoffset(void);
|
|
unsigned long calibrate_div64_gettimeoffset(void);
|
|
|
|
You can use null_gettimeoffset() will gives the same time resolution as
|
|
jiffy. Or you can implement your own gettimeoffset (probably based on
|
|
some ad hoc hardware on your machine.)
|
|
|
|
c) The following sub steps assume your CPU has counter register.
|
|
Do you plan to use the CPU counter register as the timer interrupt
|
|
or use an exnternal timer?
|
|
|
|
In order to use CPU counter register as the timer interrupt source, you
|
|
must know the counter speed (mips_counter_frequency). It is usually the
|
|
same as the CPU speed or an integral divisor of it.
|
|
|
|
d) decide on whether you want to use high-level or low-level timer
|
|
interrupt routines. The low-level one is presumably faster, but should
|
|
not make too mcuh difference.
|
|
|
|
|
|
Step 2: the machine setup() function
|
|
|
|
If you supply board_time_init(), set the function poointer.
|
|
|
|
Set the function pointer board_timer_setup() (mandatory)
|
|
|
|
|
|
Step 3: implement rtc routines, board_time_init() and board_timer_setup()
|
|
if needed.
|
|
|
|
board_time_init() -
|
|
a) (optional) set up RTC routines,
|
|
b) (optional) calibrate and set the mips_counter_frequency
|
|
(only needed if you intended to use fixed_rate_gettimeoffset
|
|
or use cpu counter as timer interrupt source)
|
|
|
|
board_timer_setup() -
|
|
a) (optional) over-write any choices made above by time_init().
|
|
b) machine specific code should setup the timer irqaction.
|
|
c) enable the timer interrupt
|
|
|
|
|
|
If the RTC chip is a common chip, I suggest the routines are put under
|
|
arch/mips/libs. For example, for DS1386 chip, one would create
|
|
rtc-ds1386.c under arch/mips/lib directory. Add the following line to
|
|
the arch/mips/lib/Makefile:
|
|
|
|
obj-$(CONFIG_DDB5476) += rtc-ds1386.o
|
|
|
|
Step 4: if you are using low-level timer interrupt, change your interrupt
|
|
dispathcing code to check for timer interrupt and jump to
|
|
ll_timer_interrupt() directly if one is detected.
|
|
|
|
Step 5: Modify arch/mips/config.in and add CONFIG_NEW_TIME_C to your machine.
|
|
Modify the appropriate defconfig if applicable.
|
|
|
|
Final notes:
|
|
|
|
For some tricky cases, you may need to add your own wrapper functions
|
|
for some of the functions in time.c.
|
|
|
|
For example, you may define your own timer interrupt routine, which does
|
|
some of its own processing and then calls timer_interrupt().
|
|
|
|
You can also over-ride any of the built-in functions (gettimeoffset,
|
|
RTC routines and/or timer interrupt routine).
|
|
|
|
|
|
PORTING NOTES FOR SMP
|
|
----------------------
|
|
|
|
If you have a SMP box, things are slightly more complicated.
|
|
|
|
The time service running every jiffy is logically divided into two parts:
|
|
|
|
1) the one for the whole system (defined in timer_interrupt())
|
|
2) the one that should run for each CPU (defined in local_timer_interrupt())
|
|
|
|
You need to decide on your timer interrupt sources.
|
|
|
|
case 1) - whole system has only one timer interrupt delivered to one CPU
|
|
|
|
In this case, you set up timer interrupt as in UP systems. In addtion,
|
|
you need to set emulate_local_timer_interrupt to 1 so that other
|
|
CPUs get to call local_timer_interrupt().
|
|
|
|
THIS IS CURRENTLY NOT IMPLEMNETED. However, it is rather easy to write
|
|
one should such a need arise. You simply make a IPI call.
|
|
|
|
case 2) - each CPU has a separate timer interrupt
|
|
|
|
In this case, you need to set up IRQ such that each of them will
|
|
call local_timer_interrupt(). In addition, you need to arrange
|
|
one and only one of them to call timer_interrupt().
|
|
|
|
You can also do the low-level version of those interrupt routines,
|
|
following similar dispatching routes described above.
|
|
|
|
Note about do_gettimeoffset():
|
|
|
|
It is very likely the CPU counter registers are not sync'ed up in a SMP box.
|
|
Therefore you cannot really use the many of the existing routines that
|
|
are based on CPU counter. You should wirte your own gettimeoffset rouinte
|
|
if you want intra-jiffy resolution.
|