From 20fa8584e31d55b7f2953f917adcc190adab236f Mon Sep 17 00:00:00 2001
From: Christian Cunningham <cc@localhost>
Date: Tue, 31 Aug 2021 08:31:10 -0700
Subject: Initial Commit

---
 src/boot.S | 135 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 135 insertions(+)
 create mode 100644 src/boot.S

(limited to 'src/boot.S')

diff --git a/src/boot.S b/src/boot.S
new file mode 100644
index 0000000..f0caebc
--- /dev/null
+++ b/src/boot.S
@@ -0,0 +1,135 @@
+// To keep this in the first portion of the binary.
+.section ".text.boot"
+ 
+// Make _start global.
+.globl _start
+ 
+_start:
+reset:
+    // disable core0,1,2.
+    mrc p15, #0, r1, c0, c0, #5
+    and r1, r1, #3
+    cmp r1, #0
+    bne io_halt 
+
+    // set vector address.
+    ldr r0, =vector
+    mcR P15, 0, r0, c12, c0, 0
+
+    // save cpsr.
+    mrs r0, cpsr
+
+    // setup sp in IRQ mode.
+    bic r1, r0, #0x1f
+    orr r1, r1, #0x12
+    msr cpsr_c,r1
+    mov sp,#0x4000
+
+    // restore cpsr.
+    msr cpsr_c, r0
+
+    // setup the stack in SVC mode.
+    mov sp, #0x8000
+ 
+    // Clear out bss.
+    ldr r4, =__bss_start
+    ldr r9, =__bss_end
+    mov r5, #0
+    mov r6, #0
+    mov r7, #0
+    mov r8, #0
+    b       2f
+ 
+1:
+    // store multiple at r4.
+    stmia r4!, {r5-r8}
+ 
+    // If we are still below bss_end, loop.
+2:
+    cmp r4, r9
+    blo 1b
+
+    // Call kernel_main
+    ldr r3, =kernel_main
+    blx r3
+
+irq:
+    push {r0,r1,r2,r3,r4,r5,r6,r7,r8,r9,r10,r11,r12,lr}
+    bl a_irq_handler
+    pop  {r0,r1,r2,r3,r4,r5,r6,r7,r8,r9,r10,r11,r12,lr}
+    subs pc, lr, #4
+
+.globl io_halt
+io_halt:
+    wfi
+    b io_halt
+
+.globl enable_irq
+enable_irq:
+    cpsie i
+    bx lr
+
+.globl disable_irq
+disable_irq:
+    cpsid i
+    bx lr
+
+.align 5
+vector:
+    ldr pc, reset_handler
+    ldr pc, undefined_handler
+    ldr pc, swi_handler
+    ldr pc, prefetch_handler
+    ldr pc, data_handler
+    ldr pc, unused_handler
+    ldr pc, irq_handler
+    ldr pc, fiq_handler
+
+reset_handler:      .word reset
+undefined_handler:  .word io_halt
+swi_handler:        .word io_halt
+prefetch_handler:   .word io_halt
+data_handler:       .word io_halt
+unused_handler:     .word io_halt
+irq_handler:        .word irq
+fiq_handler:        .word io_halt
+
+.global a_irq_handler
+a_irq_handler:
+    push {lr}
+    bl disable_irq
+    // r2 = CORE0_INTERRUPT_SOURCE
+    // if r2 & 0b100000000
+    mov r2, #0x40000000
+    ldr r3, [r2, #0x60]
+    tst r3, #256
+    beq a_irq_handler.exit
+    // r2 = IRQ_PEND2
+    // r2 & 1 << 25
+    mov r2, #0xB208
+    movt r2, #0x3F00
+    ldr r3, [r2]
+    tst r3, #0x2000000
+    beq a_irq_handler.exit
+    mov r2, #0x1040
+    movt r2, #0x3F20
+    ldr r3, [r2]
+    tst r3, #16
+    beq a_irq_handler.exit
+    mov r2, #0x1000
+    movt r2, #0x3F20
+    ldrb r0, [r2]
+    push {r0}
+    bl enable_irq
+    pop {r0}
+    bl uart_char
+    ldr r0, =amsg
+    bl uart_string
+    pop {pc}
+a_irq_handler.exit:
+    bl enable_irq
+    pop {pc}
+
+.section ".data"
+amsg:
+    .asciz " a_irq_handler\n"
-- 
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