Raspberry PI 3 Model B Rev 1.2 Power Wattage

My order of USB power meter arrived a few days ago, but only today I could put it into use by plugging it in between the power supply adapter and my RPI.

The way I test the max power consumed is by creating a small C program to do infinite loop such as:

int main()
{
   while (1) {}
}

I executed it in four separate processes (open four terminals, and run the program in each one). This way I could exhaust the whole four cores in the CPU.  I also GUI desktop on the machine (LXDE).

Here what is shown by "top":




My USB power meter shows 1.17 WH, meaning in each hour it consumes 2.37 Watt or 0.00237 KWh.  If the price per kWh charged by Utility company is 12.01 cent ($0.1201/KWH), in a day I'd pay 0.00237 KWh* $0.1201/KWh * 24 hours = $‭0.006831288‬ or about $0.0068 per day.  In a month I'd pay about $0.2 minimum.

After I killed all those four infinite loop processes, the wattage did not drop.  Instead I saw it climbed to almost 2 Watt-hour.  I think over time it probably would drop back to around 2 W (idling time).

What Coronavirus Symptoms Look Like, Day By Day

https://www.youtube.com/embed/OOJqHPfG7pA

Windows Application Development on Linux

Make sure you have installed MinGW on Linux:

sudo apt install mingw-w64 gdb-mingw-w64

Optionally, for testing purpose, install also WINE:

wine-stable wine-development wine64 wine64-development

FYI, with my recent mingw32 installation, the location for needed DLL files are in :

/usr/lib/gcc/x86_64-w64-mingw32/7.3-posix/

ll /usr/lib/gcc/x86_64-w64-mingw32/7.3-posix/*.dll
-rwxr-xr-x 1 root root   482339 Mar 12  2018 /usr/lib/gcc/x86_64-w64-mingw32/7.3-posix/libatomic-1.dll*
-rwxr-xr-x 1 root root  1190750 Mar 12  2018 /usr/lib/gcc/x86_64-w64-mingw32/7.3-posix/libgcc_s_seh-1.dll*
-rwxr-xr-x 1 root root  1523015 Mar 12  2018 /usr/lib/gcc/x86_64-w64-mingw32/7.3-posix/libgomp-1.dll*
-rwxr-xr-x 1 root root  1393636 Mar 12  2018 /usr/lib/gcc/x86_64-w64-mingw32/7.3-posix/libquadmath-0.dll*
-rwxr-xr-x 1 root root   387526 Mar 12  2018 /usr/lib/gcc/x86_64-w64-mingw32/7.3-posix/libssp-0.dll*
-rwxr-xr-x 1 root root 16229690 Mar 12  2018 /usr/lib/gcc/x86_64-w64-mingw32/7.3-posix/libstdc++-6.dll*

(this path should be added into PATH to make wine able to run our compiled EXE)

Example of Makefile:


APP=MyGUI
CC=x86_64-w64-mingw32-g++
WRC=x86_64-w64-mingw32-windres

$(APP).exe : $(APP).o $(APP).res
$(CC) -mwindows $(APP).o $(APP).res -o $@

$(APP).o: $(APP).c
$(CC) -mwindows -c -o $@ $<

$(APP).res : resource.rc resource.h
$(WRC) $< -O coff -o $@

clean:
rm *.res *.o $(APP).exe



The Source code:

/*-------------------------------------------------*/
/* MyGUI.c - gui hello world                    */
/* build: gcc -mwindows MyGUI.c -o MyGUI.exe */
/*-------------------------------------------------*/
#include <windows.h>

char glpszText[1024];

LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);

/******************************************************************************
* Main entry
******************************************************************************/
int APIENTRY WinMain(HINSTANCE hInstance, 
     HINSTANCE hPrevInstance,
     LPSTR lpCmdLine,
     int nCmdShow)
{
 wsprintf(glpszText, 
   "Hello World\nGetCommandLine(): [%s]\n"
   "WinMain lpCmdLine: [%s]\n",
   lpCmdLine, GetCommandLine() );

 WNDCLASSEX wcex; 
              
  wcex.cbSize = sizeof(wcex);
 wcex.style = CS_HREDRAW | CS_VREDRAW;
 wcex.lpfnWndProc = WndProc; /* set the callback */
 wcex.cbClsExtra = 0;
 wcex.cbWndExtra = 0;
 wcex.hInstance = hInstance;
 wcex.hIcon = LoadIcon(NULL, IDI_APPLICATION);
 wcex.hCursor = LoadCursor(NULL, IDC_ARROW);
 wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
 wcex.lpszMenuName = NULL;
 wcex.lpszClassName = "MYGUI";
 wcex.hIconSm = NULL;

 if (!RegisterClassEx(&wcex))
  return FALSE; 

 HWND hWnd;
 hWnd = CreateWindow("MYGUI", "MyGUI", WS_OVERLAPPEDWINDOW,
      CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, 
      CW_USEDEFAULT, NULL, NULL, hInstance, NULL);

 if (!hWnd)
  return FALSE;

 ShowWindow(hWnd, nCmdShow);
 UpdateWindow(hWnd);

 MSG msg;
 /* main loop */
 while (GetMessage(&msg, NULL, 0, 0)) 
 {
  /* we can intercept keystrokes here too if we want */
  TranslateMessage(&msg);
  DispatchMessage(&msg);
 }

 return msg.wParam;
}


/******************************************************************************
* Main callback
******************************************************************************/
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
 PAINTSTRUCT ps;
 HDC hdc;
                                                 
 switch (message) 
 {
  case WM_PAINT:
   hdc = BeginPaint(hWnd, &ps);
   RECT rt;
   GetClientRect(hWnd, &rt);
   DrawText(hdc, glpszText, strlen(glpszText), &rt, DT_TOP | DT_LEFT);
   EndPaint(hWnd, &ps);
   break;

  case WM_DESTROY:
   PostQuitMessage(0);
   break;
    
  default:
   /* for everything else unhandled, do this */
   return DefWindowProc(hWnd, message, wParam, lParam);
   
 }
   
 return 0;
   
}

To run:

wine64 MyGUI.exe

If we find issue that WINE could not find some MinGW's *.dll, create soft links in WINE's system directory to the MinGW's dll:

pushd ~/.wine/drive_c/windows/system
cp -s /usr/lib/gcc/i686-w64-mingw32/7.3-win32/*.dll .
popd



To debug the EXE:

i686-w64-mingw32-gdb <EXE code>

To list (dir command) file names sorted by their name's length

Suppose we want to list certain files (or all files in a directory), but sorted ascending by their filename's length.

The following small script meets the purpose:

First, create a PowerShell script, say, dirnamesize.ps1 with its content as below:

param (
   [string]$dirpath = "."
)

gci $dirpath | select-object name, @{Name="Nlength";Expression={$_.Name.Length}} | sort-object Nlength


Second, create a normal DOS shell file to call that PowerShell (so we don't need to open PowerShell), say, dirnamesize.cmd with the content:

set DIRPATH=%*

@if "%DIRPATH%"=="" (
    powershell dirnamesize.ps1
) else (
    powershell dirnamesize.ps1 -dirpath %DIRPATH%
)


Example:

C:\Windows>dirname *.xml

Name                        Nlength
----                        -------
Education.xml                    13
ServerRdsh.xml                   14
Enterprise.xml                   14
Professional.xml                 16
ProfessionalEducation.xml        25
ProfessionalWorkstation.xml      27

Example of Intrusive Singly Linked List

#include <stdio.h>
#include <stdlib.h>
#include <stddef.h>



typedef struct list_item {
    int val;
    void *next;
} list_item;


typedef struct List {
    list_item *head;
    list_item *prev;
} List;


list_item *create_list_item(int val)
{
    list_item *p = (list_item *)malloc(sizeof(list_item));
    if (p)
    {
        p->val = val;
        p->next = NULL;
    }
    return p;
}


void add_list_item_into_node(List *list, int val)
{
    list_item *newlist_item = create_list_item(val);
    if (list->prev != NULL)
    {
        list->prev->next = newlist_item;
        list->prev = newlist_item;
    }
    else
    {
        list->head = newlist_item;
        list->prev = newlist_item;
        printf("FIRST! head==prev ? %d, %p\n", list->head==list->prev, list->head);
    }

    printf("%p added; head=%p, prev=%p\n", newlist_item, list->head, list->prev);
}


void init_list(List *l)
{
    l->head = l->prev = NULL;
}


void clear_list(List *l)
{
    list_item *p = l->head;
    while (p != NULL)
    {
        list_item *pn = (list_item *)p->next; 
        printf("Freeing %p, next p is=%p\n", p, pn);
        free(p);
        p = pn;
    }
    l->head = l->prev = NULL;
}


typedef void (*callback_t)(list_item *);

void print(list_item *p)
{
    printf("p=%p: val=%d\n", p, p->val);
}

void iterate(List *list, callback_t cbk)
{
    list_item *p = list->head;
    while (p)
    {
        cbk(p);
        p = p->next;
    }
}

int main()
{
    List mylist;
    init_list(&mylist);

    for(int i=0; i<10; ++i)
    {
        add_list_item_into_node(&mylist, i*2+1);
    }

   iterate(&mylist, print);

    // cleanup; starting from head
    printf("Cleaning up!\n");
    clear_list(&mylist);
    iterate(&mylist, print);

    printf("head = %p, prev=%p\n", mylist.head, mylist.prev);
}

Unique Pointer (Smart Pointer)

The following example shows how to use unique_ptr which semantically 'moves' the data during assignment:

#include <iostream>
#include <memory>


using namespace std;


class MyClass
{
public:

#if COMPILE_ERROR
    MyClass
    (
        std::unique_ptr<int> const &  pOpt = std::unique_ptr<int>(nullptr) 
    ) : m_ptr(std::move(pOpt))
    {
    }
#else
    explicit MyClass
    ( 
        std::unique_ptr<int> pOpt = std::unique_ptr<int>(nullptr)
    ) : m_ptr(std::move(pOpt))
    {
        std::cout << __FUNCTION__ << "() : m_ptr=" << m_ptr.get() << std::endl;
    }

    MyClass() = delete;

#endif
    friend ostream& operator<<(ostream& os, const MyClass& c);

private:
    std::unique_ptr<int>  m_ptr;
};


template<typename T>
std::unique_ptr<T>& pass_through(std::unique_ptr<T>& p)
{
    if (p != nullptr)
        std::cout << *p << std::endl;
    else
        std::cout << "nullptr" << std::endl;
    return p;
}


ostream& operator<<(ostream& os, const MyClass& c)
{
    if (c.m_ptr != nullptr)
        return os << __FUNCTION__ << "(): " <<  *c.m_ptr;
    else
        return os << __FUNCTION__ << "(): nullptr";
}


int main()
{
    std::unique_ptr<int> pInt(new int(15));

    MyClass data();
    MyClass data2(std::move(pInt));

    pass_through(pInt);
    
    std::cout << "data = " << data << std::endl;
    std::cout << "data2 = " << data2 << std::endl;
}

MyClass() : m_ptr=0x7430d0

nullptr

data = 1

data2 = operator<<(): 15