.section .text.init
.globl _start
.type _start, @function
_start:
    la sp, __stack_top

    # Zero .bss
    la t0, __bss_start
    la t1, __bss_end
1:
    bgeu t0, t1, 2f
    sw zero, 0(t0)
    addi t0, t0, 4
    j 1b

2:
    call main

3:
    j 3b

.size _start, .-_start


.section .text
.globl trap_entry
.type trap_entry, @function
trap_entry:
    # Save full integer context (except x0/x2) because an interrupt can
    # preempt code with live values in any register, not just caller-saved.
    addi sp, sp, -128
    sw   ra, 124(sp)
    sw   gp, 120(sp)
    sw   tp, 116(sp)
    sw   t0, 112(sp)
    sw   t1, 108(sp)
    sw   t2, 104(sp)
    sw   s0, 100(sp)
    sw   s1,  96(sp)
    sw   a0,  92(sp)
    sw   a1,  88(sp)
    sw   a2,  84(sp)
    sw   a3,  80(sp)
    sw   a4,  76(sp)
    sw   a5,  72(sp)
    sw   a6,  68(sp)
    sw   a7,  64(sp)
    sw   s2,  60(sp)
    sw   s3,  56(sp)
    sw   s4,  52(sp)
    sw   s5,  48(sp)
    sw   s6,  44(sp)
    sw   s7,  40(sp)
    sw   s8,  36(sp)
    sw   s9,  32(sp)
    sw   s10, 28(sp)
    sw   s11, 24(sp)
    sw   t3,  20(sp)
    sw   t4,  16(sp)
    sw   t5,  12(sp)
    sw   t6,   8(sp)

    csrr t0, mcause
    li   t1, 0x80000007      # machine timer interrupt (RV32)
    bne  t0, t1, 1f
    call timer_isr           # C function that ACKs/clears the timer so i_timer_irq goes low
1:
    lw   t6,   8(sp)
    lw   t5,  12(sp)
    lw   t4,  16(sp)
    lw   t3,  20(sp)
    lw   s11, 24(sp)
    lw   s10, 28(sp)
    lw   s9,  32(sp)
    lw   s8,  36(sp)
    lw   s7,  40(sp)
    lw   s6,  44(sp)
    lw   s5,  48(sp)
    lw   s4,  52(sp)
    lw   s3,  56(sp)
    lw   s2,  60(sp)
    lw   a7,  64(sp)
    lw   a6,  68(sp)
    lw   a5,  72(sp)
    lw   a4,  76(sp)
    lw   a3,  80(sp)
    lw   a2,  84(sp)
    lw   a1,  88(sp)
    lw   a0,  92(sp)
    lw   s1,  96(sp)
    lw   s0, 100(sp)
    lw   t2, 104(sp)
    lw   t1, 108(sp)
    lw   t0, 112(sp)
    lw   tp, 116(sp)
    lw   gp, 120(sp)
    lw   ra, 124(sp)
    addi sp, sp, 128
    mret