Altera DE1-SoC - Page 18

DE1-SOC COMPUTER SYSTEM WITH NIOS II For Quartus II 15.0
/********************************************************************************
* RESET SECTION
* The Monitor Program automatically places the ".reset" section at the reset location
* specified in the CPU settings in Qsys.
* Note: "ax" is REQUIRED to designate the section as allocatable and executable.
*/
.section .reset, "ax"
movia r2, _start
jmp r2 /* branch to main program */
/********************************************************************************
* EXCEPTIONS SECTION
* The Monitor Program automatically places the ".exceptions" section at the
* exception location specified in the CPU settings in Qsys.
* Note: "ax" is REQUIRED to designate the section as allocatable and executable.
*/
.section .exceptions, "ax"
.global EXCEPTION_HANDLER
EXCEPTION_HANDLER:
subi sp, sp, 16 /* make room on the stack */
stw et, 0(sp)
rdctl et, ctl4
beq et, r0, SKIP_EA_DEC /* interrupt is not external */
subi ea, ea, 4 /* must decrement ea by one instruction */
/* for external interrupts, so that the */
/* interrupted instruction will be run after eret */
SKIP_EA_DEC:
stw ea, 4(sp) /* save all used registers on the Stack */
stw ra, 8(sp) /* needed if call inst is used */
stw r22, 12(sp)
rdctl et, ctl4
bne et, r0, CHECK_LEVEL_0 /* exception is an external interrupt */
NOT_EI: /* exception must be unimplemented instruction or TRAP */
br END_ISR /* instruction. This code does not handle those cases */
Figure 17. Reset and exception handler assembly language code (Part a).
18 Altera Corporation - University Program
2015