Question

我在https://playground.arduino.cc/Code/AvailableMemory中看到了freeMemory函数，并且似乎使用了__brkval之类的东西。但是，我根本找不到该宏或变量在哪里定义：

$ grep -ri brkval /c/arduino-1.8.8/ --include='*.c' --include='*.h'
/c/arduino-1.8.8/libraries/Robot_Control/src/Fat16util.h:  extern int* __brkval;
/c/arduino-1.8.8/libraries/Robot_Control/src/Fat16util.h:  if (reinterpret_cast<int>(__brkval) == 0) {
/c/arduino-1.8.8/libraries/Robot_Control/src/Fat16util.h:                  - reinterpret_cast<int>(__brkval);
/c/arduino-1.8.8/libraries/SD/src/utility/SdFatUtil.h:  extern int* __brkval;
/c/arduino-1.8.8/libraries/SD/src/utility/SdFatUtil.h:  if (reinterpret_cast<int>(__brkval) == 0) {
/c/arduino-1.8.8/libraries/SD/src/utility/SdFatUtil.h:                  - reinterpret_cast<int>(__brkval);

$ grep -ri brkval /c/avr-gcc-8.2.0-x64-mingw/ --include='*.c' --include='*.h'
# nothing

$ grep -ri brkval /c/Program\ Files\ \(x86\)/Atmel/Studio/ --include='*.c' --include='*.h'
# nothing

$ grep -ri brkval /c/cvavr/ --include='*.c'
# nothing

也就是说，只有Arduino IDE对此有一些引用，但仅作为extern int*引用，它没有定义。

最近，我从https://github.com/greiman/SdFat/blob/master/src/FreeStack.h进行了一些详细的解释：

/** boundary between stack and heap. */
extern char *__brkval;

...但是同样，没有定义。

那么该变量或宏在哪里定义？

编辑：根据评论，搜索所有文件：

$ grep -ri brkval /c/cvavr/
# nothing

$ grep -ri brkval /c/Program\ Files\ \(x86\)/Atmel/Studio/
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avr25/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avr25/tiny-stack/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avr3/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avr31/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avr35/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avr4/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avr5/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avr51/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avr6/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avrtiny/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avrxmega2/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avrxmega3/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avrxmega3/short-calls/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avrxmega4/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avrxmega5/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avrxmega6/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/avrxmega7/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/libc.a matches
Binary file /c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/avr/lib/tiny-stack/libc.a matches
/c/Program Files (x86)/Atmel/Studio/7.0/toolchain/avr8/avr8-gnu-toolchain/doc/avr-libc/avr-libc-user-manual/stdlib__private_8h_source.html:<a name="l00045"></a>00045 <span class="keyword">extern</span> <span class="keywordtype">char</span> *__brkval;      <span class="comment">/* first location not yet allocated */</span>

$ grep -ri brkval /c/avr-gcc-8.2.0-x64-mingw/
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avr25/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avr25/tiny-stack/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avr3/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avr31/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avr35/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avr4/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avr5/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avr51/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avr6/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avrtiny/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avrxmega2/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avrxmega4/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avrxmega5/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avrxmega6/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/avrxmega7/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/libc.a matches
Binary file /c/avr-gcc-8.2.0-x64-mingw/avr/lib/tiny-stack/libc.a matches

$ grep -ri brkval /c/arduino-1.8.8/
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avr25/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avr25/tiny-stack/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avr3/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avr31/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avr35/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avr4/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avr5/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avr51/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avr6/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avrtiny/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avrxmega2/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avrxmega3/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avrxmega3/short-calls/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avrxmega4/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avrxmega5/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avrxmega6/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/avrxmega7/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/libc.a matches
Binary file /c/arduino-1.8.8/hardware/tools/avr/avr/lib/tiny-stack/libc.a matches
/c/arduino-1.8.8/libraries/Robot_Control/src/Fat16util.h:  extern int* __brkval;
/c/arduino-1.8.8/libraries/Robot_Control/src/Fat16util.h:  if (reinterpret_cast<int>(__brkval) == 0) {
/c/arduino-1.8.8/libraries/Robot_Control/src/Fat16util.h:                  - reinterpret_cast<int>(__brkval);
/c/arduino-1.8.8/libraries/SD/src/utility/SdFatUtil.h:  extern int* __brkval;
/c/arduino-1.8.8/libraries/SD/src/utility/SdFatUtil.h:  if (reinterpret_cast<int>(__brkval) == 0) {
/c/arduino-1.8.8/libraries/SD/src/utility/SdFatUtil.h:                  - reinterpret_cast<int>(__brkval);

Answer 1

还有许多其他人也有同样的问题。并指出，用最简单的术语来说，它用于标记堆栈和堆内存之间的边界。以下是一些相关讨论，其内容包括__brkval：

Arduino: Question about memory allocation analysis 。
Free Memory Questions, Arduino 。
Arduino:You know you have a memory problem when... 。
AVRGCC: Monitoring stack usage 。
Arduino Playground: CorruptArrayVariablesAndMemory 。

最后一个链接至少在Arduino环境中解决了您的主要问题：

添加了内存事件探查器功能（请注意，它通过 MemoryFree.h 使用freeMemory，这也在上面的线程中提供），并且起始数组大小为100元素（400字节）：

// minitest.pde

static unsigned long mydata_count;

static const long SERSPEED=115200;
static const int SIZE=100;
static const char RSTSTR[] = "RESET!!";

static unsigned long mydata[SIZE];

#include <MemoryFree.h>

extern unsigned int __data_start;
extern unsigned int __data_end;
extern unsigned int __bss_start;
extern unsigned int __bss_end;
extern unsigned int __heap_start;
//extern void *__malloc_heap_start; --> apparently already declared as char*
//extern void *__malloc_margin; --> apparently already declared as a size_t
extern void *__brkval;

AVR的__brkval是什么，在哪里定义？

1 个答案: