gem5/system/arm/aarch64_bootloader/boot.S

/*
 * boot.S - simple register setup code for stand-alone Linux booting
 *
 * Copyright (C) 2012 ARM Limited. All rights reserved.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE.txt file.
 */

        .text

        .globl	_start
_start:
        /*
         * EL3 initialisation
         */
        mrs	x0, CurrentEL
        cmp	x0, #0xc			// EL3?
        b.ne	start_ns			// skip EL3 initialisation

        mov	x0, #0x30			// RES1
        orr	x0, x0, #(1 << 0)		// Non-secure EL1
        orr	x0, x0, #(1 << 8)		// HVC enable
        orr	x0, x0, #(1 << 10)		// 64-bit EL2
        msr	scr_el3, x0

        msr	cptr_el3, xzr			// Disable copro. traps to EL3

        ldr	x0, =CNTFRQ
        msr	cntfrq_el0, x0

        /*
         * Check for the primary CPU to avoid a race on the distributor
         * registers.
         */
        mrs	x0, mpidr_el1
        tst	x0, #15
        b.ne	1f				// secondary CPU

        ldr	x1, =GIC_DIST_BASE		// GICD_CTLR
        mov	w0, #3				// EnableGrp0 | EnableGrp1
        str	w0, [x1]

1:	ldr	x1, =GIC_DIST_BASE + 0x80	// GICD_IGROUPR
        mov	w0, #~0				// Grp1 interrupts
        str	w0, [x1], #4
        b.ne	2f				// Only local interrupts for secondary CPUs
        str	w0, [x1], #4
        str	w0, [x1], #4

2:	ldr	x1, =GIC_CPU_BASE		// GICC_CTLR
        ldr	w0, [x1]
        mov	w0, #3				// EnableGrp0 | EnableGrp1
        str	w0, [x1]

        mov	w0, #1 << 7			// allow NS access to GICC_PMR
        str	w0, [x1, #4]			// GICC_PMR

        msr	sctlr_el2, xzr

        /*
         * Prepare the switch to the EL2_SP1 mode from EL3
         */
        ldr	x0, =start_ns			// Return after mode switch
        mov	x1, #0x3c9			// EL2_SP1 | D | A | I | F
        msr	elr_el3, x0
        msr	spsr_el3, x1
        eret

start_ns:
        /*
         * Kernel parameters
         */
        mov	x0, xzr
        mov	x1, xzr
        mov	x2, xzr
        mov	x3, xzr

        mrs	x4, mpidr_el1
        tst	x4, #15
        b.eq	2f

        /*
         * Secondary CPUs
         */
1:	wfe
        ldr	x4, =PHYS_OFFSET + 0xfff8
        ldr     x4, [x4]
        cbz	x4, 1b
        br	x4				// branch to the given address

2:
        /*
         * UART initialisation (38400 8N1)
         */
        ldr	x4, =UART_BASE			// UART base
        mov	w5, #0x10			// ibrd
        str	w5, [x4, #0x24]
        mov	w5, #0xc300
        orr	w5, w5, #0x0001			// cr
        str	w5, [x4, #0x30]

        /*
         * CLCD output site MB
         */
        ldr	x4, =SYSREGS_BASE
        ldr	w5, =(1 << 31) | (1 << 30) | (7 << 20) | (0 << 16)	// START|WRITE|MUXFPGA|SITE_MB
        str	wzr, [x4, #0xa0]		// V2M_SYS_CFGDATA
        str	w5, [x4, #0xa4]			// V2M_SYS_CFGCTRL

        // set up the arch timer frequency
        //ldr	x0, =CNTFRQ
        //msr	cntfrq_el0, x0

        /*
         * Primary CPU
         */
        ldr	x0, =PHYS_OFFSET + 0x8000000	 // device tree blob
        ldr     x6, =PHYS_OFFSET + 0x80000       // kernel start address
        br	x6

        .ltorg

        .org	0x200