usb_init.s

/*
 * Copyright (c) 2018 Atmosphère-NX
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms and conditions of the GNU General Public License,
 * version 2, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope 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.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
.section .text.start
.align 4
 
.globl _start
 
_start:
  bl restore_svc_vector
  adr r0, (usb_init+1)
  mov lr, pc
  bx r0
  b   _crt0
 
.pool
 
.globl _crt0
.type  _crt0,%function
 
_crt0:
  ldr   r0,=0x52425430 @ RBT0
  mov   r1, #0x0
  mov   r2, #0x0
  mov   r3, #0x0
  mov   r4, #0x0
  mov   r5, #0x0
  mov   r6, #0x0
  mov   r7, #0x0
  mov   r8, #0x0
  mov   r9, #0x0
  mov   r10,#0x0
  mov   r11,#0x0
  mov   r12,#0x0
  mov   lr, #0x0
  ldr   sp,=0x40010000
  ldr   pc,=0x40010000

restore_svc_vector:
    ldr r0, =0x6000F208 /* SVC vector address */
    ldr r1, =0x40004C30 /* original SVC handler address */
    str r1, [r0]
    bx lr

.thumb

usb_init:
    push {lr} /* save return address on the stack */
    adr r0, usb_mode
    ldr r1, =0x1021B3
    ldr r2, =(set_usb_ops+1)
    mov lr, r2 /* required; early revision ARM does not have the ability to load directly into r8-r15 in thumb mode. */
    bx r1 /* get_usb_mode(&usb_mode) */
set_usb_ops:
    adr r0, usb_mode
    ldr r0, [r0]
    ldr r1, =0x102B75
    ldr r2, =(usb_initialize+1)
    mov lr, r2
    bx r1 /* set_usb_ops(usb_mode) */
usb_initialize:
    ldr r0, =0x40003114 /* r0 = &g_usb_ops */
    ldr r0, [r0, #4] /* load usb_initialize func ptr from usb_ops */
    ldr r1, =(charger_setup+1)
    mov lr, r1
    bx r0 /* usb_ops->usb_initialize() */
charger_setup:
    ldr r0, =0x40003114 /* r0 = &g_usb_ops */
    mov r1, #1
    strb r1, [r0, #1] /* set is_initialized flag to 1 */
    strb r1, [r0, #2] /* set buffer to 1; causes rcm_read_command_and_payload() to be called immediately */
    ldr r0, =0x104283
    ldr r1, =(handle_rcm+1)
    mov lr, r1
    bx r0
handle_rcm:
    ldr r0, =0x40003114 /* r0 = &g_usb_ops */
    pop {r1} /* set r1 to the return address */
    str r1, [r0, #0x10] /* replace read_ep1_out_finish with a jump to return address */
    mov r0, #0 /* this seems to be an "rcm reason" flag. Doesn't matter how it's set */
    mov r1, r0 /* set other args to 0 as they are unused for our purposes. */
    mov r2, r0
    mov r3, r0
    ldr r4, =0x102897 /* handle_rcm(0, 0, 0, 0) */
    bx r4
.pool

usb_mode: