1 ; /*
2    * ; * FreeRTOS Kernel V11.1.0
3    * ; * Copyright (C) 2021 Amazon.com, Inc. or its affiliates. All Rights Reserved.
4    * ; *
5    * ; * SPDX-License-Identifier: MIT
6    * ; *
7    * ; * Permission is hereby granted, free of charge, to any person obtaining a copy of
8    * ; * this software and associated documentation files (the "Software"), to deal in
9    * ; * the Software without restriction, including without limitation the rights to
10    * ; * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
11    * ; * the Software, and to permit persons to whom the Software is furnished to do so,
12    * ; * subject to the following conditions:
13    * ; *
14    * ; * The above copyright notice and this permission notice shall be included in all
15    * ; * copies or substantial portions of the Software.
16    * ; *
17    * ; * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
18    * ; * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
19    * ; * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
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21    * ; * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
22    * ; * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
23    * ; *
24    * ; * https://www.FreeRTOS.org
25    * ; * https://github.com/FreeRTOS
26    * ; *
27    * ; */
28 EXTERN pxCurrentTCB
29 EXTERN ulCriticalNesting
30 
31 ;
32 Context save and restore macro definitions
33 ;
34 
35 portSAVE_CONTEXT MACRO
36 
37 ;
38 Push R0 as we are going to use the register.
39    STMDB SP !, {
40     R0
41 }
42 
43 Set R0 to point to the task stack pointer.
44    STMDB SP, {
45     SP
46 }
47 ^
48 NOP
49 SUB SP, SP, # 4
50 LDMIA SP !, {
51     R0
52 }
53 
54 ;
55 Push the return address onto the stack.
56           STMDB R0 !, {
57            LR
58        }
59 
60        Now we have saved LR we can use it instead of R0.
61           MOV LR, R0
62 
63 ;
64 
65 Pop R0 so we can save it onto the system mode stack.
66    LDMIA SP !, {
67     R0
68 }
69 
70 Push all the system mode registers onto the task stack.
71    STMDB LR, {
72     R0 - LR
73 }
74 ^
75 NOP
76 SUB LR, LR, # 60
77 
78 ;
79 Push the SPSR onto the task stack.
80    MRS R0, SPSR
81 STMDB LR !, {
82     R0
83 }
84 
85 LDR R0, = ulCriticalNesting
86           LDR R0, [ R0 ]
87 STMDB LR !, {
88     R0
89 }
90 
91 Store the new top of stack
92 
93 for the task.
94    LDR R1, = pxCurrentTCB
95              LDR R0, [ R1 ]
96 STR LR, [ R0 ]
97 
98 ENDM
99 
100 
101 portRESTORE_CONTEXT MACRO
102 
103 ;
104 Set the LR to the task stack.
105    LDR R1, = pxCurrentTCB
106              LDR R0, [ R1 ]
107 LDR LR, [ R0 ]
108 
109 ;
110 The critical nesting depth is the first item on the stack.
111    ;
112 Load it into the ulCriticalNesting variable.
113    LDR R0, = ulCriticalNesting
114              LDMFD LR !, {
115     R1
116 }
117 
118 STR R1, [ R0 ]
119 
120 ;
121 Get the SPSR from the stack.
122    LDMFD LR !, {
123     R0
124 }
125 MSR SPSR_cxsf, R0
126 
127 ;
128 Restore all system mode registers
129 
130 for the task.
131    LDMFD LR, {
132     R0 - R14
133 }
134 
135 ^
136 NOP
137 
138 ;
139 Restore the return address.
140           LDR LR, [ LR, # + 60 ]
141 
142 ;
143 
144 And return -correcting the offset in the LR to obtain the
145 ;
146 
147 correct address.
148    SUBS PC, LR, # 4
149 
150 ENDM
151