+++ /dev/null
-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
-
- 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) 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_hpt_frequency
-
- b) plat_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_hpt_frequency - It must be definied if the board
- is using CPU counter for timer interrupt.
-
-
-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.
-
- 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_hpt_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.
-
-
-Step 3: implement rtc routines, board_time_init() and plat_timer_setup()
- if needed.
-
- board_time_init() -
- a) (optional) set up RTC routines,
- b) (optional) calibrate and set the mips_hpt_frequency
- (only needed if you intended to use cpu counter as timer interrupt
- source)
-
- plat_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 (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.
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