1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
|
Microsoft's Azure RTOS ThreadX for ARMv7-M
(Cortex-M3, Cortex-M4, Cortex-M7)
Using the GNU Tools
1. Building the ThreadX run-time Library
Navigate to the "example_build" directory. Ensure that
you have setup your path and other environment variables necessary for the ARM
GNU compiler. At this point you may run the build_threadx.bat batch file.
This will build the ThreadX run-time environment in the "example_build"
directory.
You should observe assembly and compilation of a series of ThreadX source
files. At the end of the batch file, they are all combined into the
run-time library file: tx.a. This file must be linked with your
application in order to use ThreadX.
2. Demonstration System
The ThreadX demonstration is designed to execute on Cortex-M evaluation boards
or on a dedicated simulator.
Building the demonstration is easy, simply execute the build_threadx_sample.bat
batch file while inside the "example_build" directory.
You should observe the compilation of sample_threadx.c (which is the demonstration
application) and linking with tx.a. The resulting file sample_threadx.out is a binary
file that can be downloaded and executed on the a simulator, or downloaded to a board.
3. System Initialization
The entry point in ThreadX for the Cortex-M using gnu tools uses the standard GNU
Cortex-M reset sequence. From the reset vector the C runtime will be initialized.
The ThreadX tx_initialize_low_level.S file is responsible for setting up
various system data structures, the vector area, and a periodic timer interrupt
source.
In addition, _tx_initialize_low_level determines the first available
address for use by the application, which is supplied as the sole input
parameter to your application definition function, tx_application_define.
4. Register Usage and Stack Frames
The following defines the saved context stack frames for context switches
that occur as a result of interrupt handling or from thread-level API calls.
All suspended threads have the same stack frame in the Cortex-M version of
ThreadX. The top of the suspended thread's stack is pointed to by
tx_thread_stack_ptr in the associated thread control block TX_THREAD.
Non-FPU Stack Frame:
Stack Offset Stack Contents
0x00 lr Interrupted lr (lr at time of PENDSV)
0x04 r4 Software stacked GP registers
0x08 r5
0x0C r6
0x10 r7
0x14 r8
0x18 r9
0x1C r10
0x20 r11
0x24 r0 Hardware stacked registers
0x28 r1
0x2C r2
0x30 r3
0x34 r12
0x38 lr
0x3C pc
0x40 xPSR
FPU Stack Frame (only interrupted thread with FPU enabled):
Stack Offset Stack Contents
0x00 lr Interrupted lr (lr at time of PENDSV)
0x04 s16 Software stacked FPU registers
0x08 s17
0x0C s18
0x10 s19
0x14 s20
0x18 s21
0x1C s22
0x20 s23
0x24 s24
0x28 s25
0x2C s26
0x30 s27
0x34 s28
0x38 s29
0x3C s30
0x40 s31
0x44 r4 Software stacked registers
0x48 r5
0x4C r6
0x50 r7
0x54 r8
0x58 r9
0x5C r10
0x60 r11
0x64 r0 Hardware stacked registers
0x68 r1
0x6C r2
0x70 r3
0x74 r12
0x78 lr
0x7C pc
0x80 xPSR
0x84 s0 Hardware stacked FPU registers
0x88 s1
0x8C s2
0x90 s3
0x94 s4
0x98 s5
0x9C s6
0xA0 s7
0xA4 s8
0xA8 s9
0xAC s10
0xB0 s11
0xB4 s12
0xB8 s13
0xBC s14
0xC0 s15
0xC4 fpscr
5. Improving Performance
The distribution version of ThreadX is built without any compiler optimizations.
This makes it easy to debug because you can trace or set breakpoints inside of
ThreadX itself. Of course, this costs some performance. To make it run faster,
you can change the build_threadx.bat file to remove the -g option and enable
all compiler optimizations.
In addition, you can eliminate the ThreadX basic API error checking by
compiling your application code with the symbol TX_DISABLE_ERROR_CHECKING
defined.
6. Interrupt Handling
ThreadX provides complete and high-performance interrupt handling for Cortex-M
targets. There are a certain set of requirements that are defined in the
following sub-sections:
6.1 Vector Area
The Cortex-M vectors start at the label __tx_vectors or similar. The application may modify
the vector area according to its needs. There is code in tx_initialize_low_level() that will
configure the vector base register.
6.2 Managed Interrupts
A ThreadX managed interrupt is defined below. By following these conventions, the
application ISR is then allowed access to various ThreadX services from the ISR.
Here is the standard template for managed ISRs in ThreadX:
.global __tx_IntHandler
.thumb_func
__tx_IntHandler:
; VOID InterruptHandler (VOID)
; {
PUSH {r0, lr}
; /* Do interrupt handler work here */
; /* BL <your interrupt routine in C> */
POP {r0, lr}
BX lr
; }
Note: the Cortex-M requires exception handlers to be thumb labels, this implies bit 0 set.
To accomplish this, the declaration of the label has to be preceded by the assembler directive
.thumb_func to instruct the linker to create thumb labels. The label __tx_IntHandler needs to
be inserted in the correct location in the interrupt vector table. This table is typically
located in either your runtime startup file or in the tx_initialize_low_level.S file.
7. FPU Support
ThreadX for Cortex-M supports automatic ("lazy") VFP support, which means that applications threads
can simply use the VFP and ThreadX automatically maintains the VFP registers as part of the thread
context - no additional setup by the application.
8. Revision History
For generic code revision information, please refer to the readme_threadx_generic.txt
file, which is included in your distribution. The following details the revision
information associated with this specific port of ThreadX:
06-02-2021 Initial ThreadX version 6.1.7 for Cortex-M using GNU tools.
Copyright(c) 1996-2021 Microsoft Corporation
https://azure.com/rtos
|
