The presence of the main function is a hardcoded trigger in sdcc that causes
the interrupt vectors and atomic rollback helpers to be generated as part of
compilation of the file containing the main function.
This makes sure the runtime library is correctly initialized and reduces
crtstart.asm to contain only the banked call helpers.
To ensure that the __interrupt_vect in area HOME is located at the beginning
of the firmware, the linker flags are updated to set the HOME start to
0x00000 and the linker object order is modified to have rtlplayground.rel
first.
Generated code in rtlplayground.asm:
```
;--------------------------------------------------------
; interrupt vector
;--------------------------------------------------------
.area HOME (CODE)
__interrupt_vect:
ljmp __sdcc_gsinit_startup
ljmp _isr_ext0
.ds 5
ljmp _isr_timer0
.ds 5
ljmp _isr_ext1
.ds 5
reti
.ds 7
ljmp _isr_serial
.ds 5
ljmp _isr_timer2
.ds 5
reti
.ds 7
reti
.ds 7
ljmp _isr_ext2
.ds 5
ljmp _isr_ext3
; restartable atomic support routines
.ds 2
sdcc_atomic_exchange_rollback_start::
nop
nop
sdcc_atomic_exchange_pdata_impl:
movx a, @r0
mov r3, a
mov a, r2
movx @r0, a
sjmp sdcc_atomic_exchange_exit
nop
nop
sdcc_atomic_exchange_xdata_impl:
movx a, @dptr
mov r3, a
mov a, r2
movx @dptr, a
sjmp sdcc_atomic_exchange_exit
sdcc_atomic_compare_exchange_idata_impl:
mov a, @r0
cjne a, ar2, .+#5
mov a, r3
mov @r0, a
ret
nop
sdcc_atomic_compare_exchange_pdata_impl:
movx a, @r0
cjne a, ar2, .+#5
mov a, r3
movx @r0, a
ret
nop
sdcc_atomic_compare_exchange_xdata_impl:
movx a, @dptr
cjne a, ar2, .+#5
mov a, r3
movx @dptr, a
ret
sdcc_atomic_exchange_rollback_end::
sdcc_atomic_exchange_gptr_impl::
jnb b.6, sdcc_atomic_exchange_xdata_impl
mov r0, dpl
jb b.5, sdcc_atomic_exchange_pdata_impl
sdcc_atomic_exchange_idata_impl:
mov a, r2
xch a, @r0
mov dpl, a
ret
sdcc_atomic_exchange_exit:
mov dpl, r3
ret
sdcc_atomic_compare_exchange_gptr_impl::
jnb b.6, sdcc_atomic_compare_exchange_xdata_impl
mov r0, dpl
jb b.5, sdcc_atomic_compare_exchange_pdata_impl
sjmp sdcc_atomic_compare_exchange_idata_impl
```
Downside of Timer0 is, we have to manually reload
the timer value. Timer2 can do that automaticly.
This saves a lot of time in the interrupt-handler
of the Timer.
Currently Timer2 is used for baudrate-generation
but in a separete commit this is moved to Timer1.
Tobias Diedrich
René van Dorst
logicog