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|
!
! start_time.s - illustrate use of the timer device
!
! this file should be loaded using the -s flag; after user
! program has been loaded.
!
! some versions of the gnu linker (ld) like to start SPARC programs
! at 0x2020, others like 0x20. If your linker likes 0x20,
! this code won't work -- 0x20 is in the middle of the exception
! vectors.... usually, setting an explicit entry point forces the
! linker to use 0x2020 as an entry point -- to do this, use the
! -e start option to ld
!
!
! One word of caution.... make sure that the user level program
! starts at location 0x20 -- or change the definition
! MAIN
MAIN = 0x20 ! start address of the user program
TIMER_VECTOR = 0x110
TIMER_DEVICE = 1040 << 10
TICKS = 400 ! number of clock ticks before an interrupt
SAFE = 4 ! the address of a safe location in the user's
! data segment -- the timer interrupt will
! increment this value
!----------------------------------------------------------------------
! start:
! install a handler for the timer device
! start the timer
! then start the user program
!
.text
.global start
start:
save
! install the timer vector
! NOTE: we need to load instructions from the
! supervisor text space and store instructions to the
! supervisor text space
! supervisor text is address space 9
set 8, %r3
set timer_vect, %r2
ldda [%r2]9, %r4
ldda [%r2+%r3]9, %r6
set TIMER_VECTOR, %r2
stda %r4, [%r2]9
stda %r6, [%r2+%r3]9
! setup for a rett that will start the user program at the
! address MAIN
set MAIN, %r17
set MAIN+4, %r18
jmpl %r17, %r0
rett %r18
!----------------------------------------------------------------------
! timer_vect:
! the code to be placed in the timer interrupt vector
!
! this code uses a jump and link instead of a branch
! to avoid problems with relative addresses
! remember, we're going to copy this code to a different
! location.....
!
.text
.align 8
timer_vect:
set timer, %l3 ! 2 words
jmpl %l3, %r0 ! 1 word
nop ! 1 word
!----------------------------------------------------------------------
! timer:
! the timer interrupt handler
!
.text
timer:
! increment a value in the user address space, so they can
! observe the changes
set SAFE, %l0
lda [%l0]10, %l1
inc %l1
sta %l1, [%l0]10
! return to the user instruction that was just about to
! execute before the interrupt was detected
jmpl %r17, %r0
rett %r18
|
