1//
2//  Copyright (c) 2011-2012, ARM Limited. All rights reserved.
3//
4//  This program and the accompanying materials
5//  are licensed and made available under the terms and conditions of the BSD License
6//  which accompanies this distribution.  The full text of the license may be found at
7//  http://opensource.org/licenses/bsd-license.php
8//
9//  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
10//  WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
11//
12//
13
14    EXPORT  return_from_exception
15    EXPORT  enter_monitor_mode
16    EXPORT  copy_cpsr_into_spsr
17    EXPORT  set_non_secure_mode
18
19    AREA   Helper, CODE, READONLY
20
21// r0: Monitor World EntryPoint
22// r1: MpId
23// r2: SecBootMode
24// r3: Secure Monitor mode stack
25enter_monitor_mode FUNCTION
26    cmp     r3, #0                      // If a Secure Monitor stack base has not been defined then use the Secure stack
27    moveq   r3, sp
28
29    mrs     r4, cpsr                    // Save current mode (SVC) in r4
30    bic     r5, r4, #0x1f               // Clear all mode bits
31    orr     r5, r5, #0x16               // Set bits for Monitor mode
32    msr     cpsr_cxsf, r5               // We are now in Monitor Mode
33
34    mov     sp, r3                      // Set the stack of the Monitor Mode
35
36    mov     lr, r0                      // Use the pass entrypoint as lr
37
38    msr     spsr_cxsf, r4               // Use saved mode for the MOVS jump to the kernel
39
40    mov     r4, r0                      // Swap EntryPoint and MpId registers
41    mov     r0, r1
42    mov     r1, r2
43    mov     r2, r3
44
45    bx      r4
46    ENDFUNC
47
48// Return-from-exception is not an interworking return, so we must do it
49// in two steps, in case r0 has the Thumb bit set.
50return_from_exception
51    adr     lr, returned_exception
52    movs    pc, lr
53returned_exception                           // We are now in non-secure state
54    bx      r0
55
56// Save the current Program Status Register (PSR) into the Saved PSR
57copy_cpsr_into_spsr
58    mrs     r0, cpsr
59    msr     spsr_cxsf, r0
60    bx      lr
61
62// Set the Non Secure Mode
63set_non_secure_mode
64    push    { r1 }
65    and     r0, r0, #0x1f     // Keep only the mode bits
66    mrs     r1, spsr          // Read the spsr
67    bic     r1, r1, #0x1f     // Clear all mode bits
68    orr     r1, r1, r0
69    msr     spsr_cxsf, r1     // write back spsr (may have caused a mode switch)
70    isb
71    pop     { r1 }
72    bx      lr                // return (hopefully thumb-safe!)
73
74dead
75    B       dead
76
77    END
78