Understanding FSRW flush

Comments

• rokicki Posts: 1,000

  2010-02-05 19:31 edited 2010-02-05 19:31

  A 0.4s delay for pflush is not normal, but it could occur every so often. Essentially, sequential writes tend to be
  fast, but the SD card can have a significant delay at various times.
  
  I would not be shocked to see a 0.4s delay for a flush every, say, 100 to 1000 writes, but most of the time
  it should be *significantly* faster than this.
  
  Note that the flush updates the data block, possibly a FAT block, and the directory block, so there's a fair
  amount of writing going on, and the wear leveling code may need to scramble to find the appropriate
  erase blocks to work with.
  
  I would drop the flush unless you *really* need it and let pclose() finish things off. If it's a perpetual loop,
  then you need to trade off buffering required vs how much data you lose to evaluate how frequently you want
  to flush.
  
  What kind of card are you using, and how do you have it formatted?
• DavidGreg Posts: 38

  2010-02-05 19:48 edited 2010-02-05 19:48

  The card is a kingston 4gb microSDHC. I didn't format it [noparse]:)[/noparse]
  
  The 0.4 seconds is very repeatable with the above code - every write/flush takes about 0.4s per the cnt output to the file. I can upload an example ifyou're interested.
  
  
  I guess i'm greedy because I want all my data at a fixed sample rate [noparse]:)[/noparse] So re-wrote this a little with two alternating buffers and a dedicated cog for acquiring the samples.
  
  It works if the repeat until loops are commented out, but of course there is no timing between the writing and the reading to the buffer. If i uncomment the repeat until loops, nothing is ever written to the file.
  
  

  
  CON
     
    _clkmode = xtal1 + pll16x                     ' Crystal and PLL settings.
    _xinfreq = 5_000_000                          ' 5 MHz crystal.
  
  OBJ
  
    sd     : "fsrw"
    log: "buffLog"
  
  
  DAT
     FileName  byte "data.bin",0
     Buff1 long 1 [noparse][[/noparse]2500]
     Buff2 long 2 [noparse][[/noparse]2500]
     flag1 byte True
     flag2 byte True   
     
  PUB go | counter, i, j, k                      
  
    sd.mount(0)
    sd.popen(@FileName, "a" )
    log.start(@Buff1,@Buff2,@flag1,@flag2)
   
     repeat
       ' repeat until (flag1 == True)
       '  Next
          
        sd.pwrite(@buff1,4*13*150)
        sd.pflush
  
       ' repeat until (flag2 == True)
       '   Next
  
        sd.pwrite(@buff2,4*13*150)
        sd.pflush
  
  

  
  
  
  

  OBJ
    mcp1   : "MCP3208"                             ' ADC Object
    mcp2   : "MCP3208"
  CON
    cpin1  =  20
    dpin1  =  21
    spin1  =  22
  
    cpin2  = 27
    dpin2  = 24
    spin2  = 26
    
  VAR
    long  Stack[noparse][[/noparse]120]                      'Stack space for new cog
    byte  Cog                            'Hold ID of cog in use, if any   
   
  PUB Start(bufAdd1,bufAdd2,fAdd1,fAdd2): Success
  {{Start new servo input process.  Return True if successful.}}
    Stop
    Success := (Cog := cognew(log(bufAdd1,bufAdd2,fAdd1,fAdd2), @Stack) + 1)
  
  PUB Stop
  {{Stop toggling process, if any.}}
    if Cog
      cogstop(Cog~ - 1)
   
  PUB Active: YesNo
  {{Return TRUE if process is active, FALSE otherwise.}}
    YesNo := Cog > 0
        
  PUB log (buffAdd1,buffAdd2,flAdd1,flAdd2) | i,j,k
    mcp1.start(dpin1,cpin1,spin1,%11111111)
    mcp2.start(dpin2,cpin2,spin2,%11111111)
  
    repeat
      Byte[noparse][[/noparse]flAdd1] := False
      repeat j from 0 to 149
         k := j*13
         LONG[noparse][[/noparse]buffAdd1][noparse][[/noparse]0+k] := cnt 
         repeat i from 0 to 7 
            LONG[noparse][[/noparse]buffAdd1][noparse][[/noparse]i+1+k] := mcp1.in(i) 
         repeat i from 0 to 3       
             LONG[noparse][[/noparse]buffAdd1][noparse][[/noparse]i+8+1+k] := mcp2.in(i)
         waitcnt(cnt + 218_560)
      Byte[noparse][[/noparse]flAdd1] := True
          
  
      Byte[noparse][[/noparse]flAdd2]:= False
      repeat j from 0 to 149
         k := j*13
         LONG[noparse][[/noparse]buffAdd2][noparse][[/noparse]0+k] := cnt 
         repeat i from 0 to 7 
            LONG[noparse][[/noparse]buffAdd2][noparse][[/noparse]i+1+k] := mcp1.in(i) 
         repeat i from 0 to 3       
             LONG[noparse][[/noparse]buffAdd2][noparse][[/noparse]i+8+1+k] := mcp2.in(i)
         waitcnt(cnt + 218_560)
      Byte[noparse][[/noparse]flAdd2] := True     
  
  

  spin

  spin

  LoggerMain_v3.spin

  709B

  spin

  spin

  buffLog.spin

  8K

  LoggerMain_v3.spin 709B

  buffLog.spin 7.6K
• rokicki Posts: 1,000

  2010-02-05 21:23 edited 2010-02-05 21:23

  Why don't you mock up the code with a fake sample generator (so I can run it without your
  MCP3208 hardware) that writes a file that includes the cnt samples (in ASCII would be nice)
  and include the file it generates in the zip. I'll run it on my hardware here and my cards and
  compare.