How could one boost sdcard access
lazarus / 43-Android

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stab · 2013-01-03 15:11

Hi all,

I'm trying to make an android app for fleetmanagement with
a map-background where you should be able to zoom and pan.
Map-data is organised as blocks in a file with some meta-data as a
header
containing information about projection, extent in world-coordinates
and resolution.
The header is followed by a table containing pointers to and sizes of
the blocks.
After that follows all the blocks that are single png-files.

Access to map-data is done through three methods of an custom object
shown below.

function TKIRObject.GetPNGImageWithInRectangle(x1, y1, x2, y2: double)
: boolean;
begin
// code to calculate input-worldcoordinates to start- and enblocks
  GetMapWithInRectangle(StartBlockNr, EndBlockNr);
end;

function TKIRObject.GetMapWithInRectangle(StartBlockNr, EndBlockNr:
LongWord) : boolean;
var
  col, row, blocknr, x, y : LongWord;
  AWidth, AHeight : integer;
  StartCol, StartRow, EndCol, EndRow, temp : LongWord;
  westStartBlockNr : integer;
  tstart1, tstart2, tstart3, tstart4, tstart5, tstart6 : tdatetime;
  tend1, tend2, tend3, tend4, tend5, tend6 : tdatetime;
  tmax1, tmax2, tmax3, tmax4, tmax5, tmax6 : tdatetime;
begin
  Result := true;

  tMax1 := 0;
  tMax2 := 0;
  tMax3 := 0;

  totBlocks := 0;

  tStart1 := Now;
 
  FPng.Clear;

// calculate startcolumn, endcolumg, startrow and endrow of resulting
pngImage built by current blocks
  BlockNrToColRow(StartBlockNr, StartCol, StartRow);
  BlockNrToColRow(EndBlockNr, EndCol, EndRow);

  westStartBlockNr := StartBlockNr;

  if StartCol > EndCol then
  begin
    temp := EndCol;
    EndCol := StartCol;
    StartCol := temp;
  end;

  if StartRow > EndRow then
  begin
    temp := EndRow;
    EndRow := StartRow;
    StartRow := temp;
  end;

// determine size of resulting pngImage
  AWidth := FInfo.BlockSizeEast * (EndCol - StartCol + 1);
  AHeight := FInfo.BlockSizeNorth * (EndRow - StartRow + 1);

  FPng.SetSize(AWidth, AHeight);

  try
    row := StartRow;
    while row < EndRow + 1 do
    begin
      col := StartCol;
      while col < EndCol + 1 do
      begin
 // determine block by current column and row
       blockNr := ColRowToBlockNr(col, row);
        if blockNr > westStartBlockNr + FNumBlocksEast - 1 then
          Break;
        tStart2 := Now;
// read block
        ReadPNGBlock(blocknr, FBlockPng);
        tEnd2 := Now;
        Inc(totBlocks);
        if FBlockPng.Width = 0 then
        begin
          inc(col);
          Continue;
        end;

//        FBlockPng.SaveToFile(ExtractFilePath(Application.Exename) +
'Read' + IntToStr(blocknr) + '.png');
        x := (col - StartCol) * FInfo.BlockSizeEast;
        y := (row - StartRow) * FInfo.BlockSizeNorth;

        tStart3 := Now;
// copy block to resulting pngImage
        FPng.Canvas.CopyRect(Rect(x, y, x + png.Width, y +
png.Height),
          FBlockPng.Canvas, Rect(0, 0, png.Width, png.Height));
//        FPng.SaveToFile(ExtractFilePath(Application.Exename) + 'Tot'
+ IntToStr(blocknr) + '.png');
        tEnd3 := Now;

        Inc(col);
      end;
      westStartBlockNr := westStartBlockNr + Finfo.BlockCountEast;

      Inc(row);
    end;

    tEnd1 := Now;
    tMax1 := tEnd1 - tStart1; // Total time for totBlocks
    tMax2 := tEnd2 - tStart2; // time to read one block ReadPNGBlock
    tMax3 := tEnd3 - tStart3; // time for FPng.Canvas.CopyRect
  except
    Result := false;
  end;
end;

procedure TKIRObject.ReadPNGBlock(BlockNum: integer; var png :
TPortableNetworkGraphic);
var
  loffset1 : LongWord;
  memStream : TMemoryStream;
begin
  png.Clear;

  if FBlockOffsetPointerArray = nil then Exit;

//We use the offset array to find the offset of the requested mapblock

  loffset1 := FBlockOffsetPointerArray[BlockNum].Position;

  FFileStream.Position := loffset1;

  FBlockSize := FBlockOffsetPointerArray[BlockNum].BlockSize;
  if FBlockSize = 0 then Exit;

  memStream := TMemoryStream.Create;
  try
    memStream.CopyFrom(FFileStream, FBlockSize);
    l := memStream.Size;
    if memStream.Size > 0 then
    begin
      memStream.Position := 0;
      png.LoadFromStream(memStream);
    end;
  finally
    FreeandNil(memStream);
  end;
end;

In method: GetMapWithInRectangle(StartBlockNr, EndBlockNr) I made
benchmark on PC and a smartphone
when retrieving a map containing 12 blocks.

Benchmark-result below:
______________________________________________________________________
__________
Device         ReadPNGBlock   FPng.Canvas.CopyRect    NumBlocks    
 TotalTime
______________________________________________________________________
__________

PC:
Win 7/64bits           4 ms                 3 ms                     
      12                 84 ms
8 Gb Ram
2.7 GHz
______________________________________________________________________
__________

Sony-Ericsson
XPeria, X10i
Android 2.3.3         36 ms              63 ms                       
     12             1258 ms   
384 Mb Ram
CPU 1 GHz
GPU Adreno 200
______________________________________________________________________
__________

Access to 12 blocks on the smartphone is almoust 15 times slower than
on PC.

I also made a test reading png:s(120kb 480x780 pixels) from disk with
LoadFrom File on PC and smartphone and
got these access-times:
PC: 47 ms   smartphone: 490ms

In this case the factor is 10

With this access-time in android, the app is almost useless.

Can someone either point at some mistake I'm doing or suggest
something to
boost speed in android?

Regards
stab

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Leledumbo · 2013-01-03 16:07

Buy a new SD card with higher classIncrease OS I/O read buffer

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stab · 2013-01-03 16:31

Thanks for answering,

Does your answer mean that you don't find any big mistake
in my code?

/stab

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stab · 2013-01-03 16:42

How do I increase OS I/O read buffer?

From my benchmark all is OK on PC but in smartphone
it might be useful.

/stab

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marcov · 2013-01-03 23:02

Is it sure it is the I/O and not the decompression in PNG?