ST9 datasheet(46/146 Pages) STMICROELECTRONICS

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ST9 USER GUIDE

.org

IT_MFT0_VECT

.word

isr_ovf_unf; ISR address on OVF /UNF

.fill

1,2,0xffff ; does not exist in MFT0 interrupt ; skip one vector

.word

isr_capt

; ISR address on capture event

.word

isr_comp

; ISR on compare event

; somewhere in the initialisation code...

;MFT0 initialisation

mft0_init:

spp

#T0C_PG

; select MFT0 control register page

-; setting of some other registers...

T0_IVR, #IT_MFT0_VECT; pointer for the vector table

-; continuation of the program...

A similar scheme applies for all other peripherals, though the number of interrupt causes may

vary, and thus the size of the pointer table.

Note:

To summarize, the table of vectors to an interrupt service routine in ROM for a given peripheral

is itself pointed to by the Interrupt Vector Register of this peripheral that must be set to the prop-

er value. This gives you an unusual degree of flexibility: a peripheral may have different interrupt

service routines at different times, without the need to add tests at the beginning of the interrupt

service routine. Let’s consider for example that we want to transfer a string of data from a pe-

ripheral. When the first byte of data comes in, we must initialise some variables to handle the

string. Then, all subsequent transfers merely copy the data from the peripheral to memory and

increment the pointer. Switching between these two modes is very easy. Initially, the IVR of the

peripheral is set to the block of vectors that point to the interrupt service routine that serves the

first time. This interrupt service routine changes the value of the IVR to another block of vectors

and returns. The next interrupt will be automatically re-routed to the other, lighter, interrupt ser-

vice routine. This reduces the execution time of this routine, since we do not need to test wheth-

er this is the first time that the interrupt service routine is called or not.

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