start.s

/*=============================================================================
Copyright (C) 2016-2017 Authors of rpi-open-firmware
All rights reserved.

This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

FILE DESCRIPTION
Entry.

A small explanation. The ROM loads bootcode.bin at 0x80000000 and jumps to
0x80000200. This region corresponds to L1/L2 cached IO and cache is never
evicted as long as we don't touch memory above that. This gives us 128KB
of memory at startup.

Exception names are from the public release from:
	brcm_usrlib\dag\vmcsx\vcfw\rtos\none\rtos_none.c

=============================================================================*/

.text

empty_space:
	.space 0x200

/* MMIO-mapped registers for the interrupt table */

.set IC0_BASE, 0x7e002000
.set IC0_VADDR, 0x7e002030

.set IC1_BASE, 0x7e002800
.set IC1_VADDR, 0x7e002830

/* main entry point */

.globl _start
.align 2
_start:
	version r0
	mov r5, r0

	/* vectors */
	mov r3, #0x1B000
	mov r1, r3

	/*
	 * populate the exception vector table using PC relative labels
	 * so the code isnt position dependent
	 */
.macro RegExceptionHandler label, exception_number
	lea r2, fleh_\label
	st r2, (r1)
	add r1, #4
.endm

	RegExceptionHandler zero, #0
	RegExceptionHandler misaligned, #1
	RegExceptionHandler dividebyzero, #2
	RegExceptionHandler undefinedinstruction, #3
	RegExceptionHandler forbiddeninstruction, #4
	RegExceptionHandler illegalmemory, #5
	RegExceptionHandler buserror, #6
	RegExceptionHandler floatingpoint, #7
	RegExceptionHandler isp, #8
	RegExceptionHandler dummy, #9
	RegExceptionHandler icache, #10
	RegExceptionHandler veccore, #11
	RegExceptionHandler badl2alias, #12
	RegExceptionHandler breakpoint, #13
	RegExceptionHandler unknown, #14
	RegExceptionHandler unknown, #15
	RegExceptionHandler unknown, #16
	RegExceptionHandler unknown, #17
	RegExceptionHandler unknown, #18
	RegExceptionHandler unknown, #19
	RegExceptionHandler unknown, #20
	RegExceptionHandler unknown, #21
	RegExceptionHandler unknown, #22
	RegExceptionHandler unknown, #23
	RegExceptionHandler unknown, #24
	RegExceptionHandler unknown, #25
	RegExceptionHandler unknown, #26
	RegExceptionHandler unknown, #27
	RegExceptionHandler unknown, #28
	RegExceptionHandler unknown, #29
	RegExceptionHandler unknown, #30
	RegExceptionHandler unknown, #31

	add r1, r3, #128
	lea r2, fleh_irq
	add r4, r3, #572

L_setup_hw_irq:
	st r2, (r1)
	add r1, #4
	ble r1, r4, L_setup_hw_irq

	/*
	 * load the interrupt and normal stack pointers. these
	 * are chosen to be near the top of the available cache memory
	 */

	mov r28, #0x1D000 
	mov sp, #0x1C000

	/* jump to C code */
	mov r0, r5
	lea r1, _start

	bl _main

/************************************************************
 * Exception Handling
 ************************************************************/

.macro SaveRegsLower 
	stm lr, (--sp)
	stm r0-r5, (--sp)
.endm

.macro SaveRegsUpper
	stm r6-r15, (--sp)
	stm r16-r23, (--sp)
.endm

.macro SaveRegsAll
	SaveRegsLower
	SaveRegsUpper
.endm

fatal_exception:
	SaveRegsUpper
	mov r0, sp
	b sleh_fatal

.macro ExceptionHandler label, exception_number
fleh_\label:
	SaveRegsLower
	mov r1, \exception_number
	b fatal_exception
.endm

	ExceptionHandler zero, #0
	ExceptionHandler misaligned, #1
	ExceptionHandler dividebyzero, #2
	ExceptionHandler undefinedinstruction, #3
	ExceptionHandler forbiddeninstruction, #4
	ExceptionHandler illegalmemory, #5
	ExceptionHandler buserror, #6
	ExceptionHandler floatingpoint, #7
	ExceptionHandler isp, #8
	ExceptionHandler dummy, #9
	ExceptionHandler icache, #10
	ExceptionHandler veccore, #11
	ExceptionHandler badl2alias, #12
	ExceptionHandler breakpoint, #13
	ExceptionHandler unknown, #14

fleh_irq:
	SaveRegsAll

	/* top of savearea */
	mov r0, sp
	mov r1, r29
	bl sleh_irq

return_from_exception:
	ldm r16-r23, (sp++)
	ldm r6-r15, (sp++)
	ldm r0-r5, (sp++)
	ld lr, (sp++)
	rti

/* include chainloader */

.align 2
.globl L_arm_code_start
L_arm_code_start:

	.incbin "arm_chainloader/build/arm_chainloader.bin"

.globl L_arm_code_end
L_arm_code_end: