MicroSD Cards and SDFS

[rsocor01]

mackrackit,

In my project, data is read from the MicroSD card and sent to a TFT LCD display. As you can imagine, speed is very important. Let's say that I have the following bytes in my TXT file and I want to read them

203
37
92

When you read these values with SDFS you get something like

FAT_dest[0] = 50     'ASCII number for "2"
FAT_dest[1] = 48     'ASCII number for "0"
FAT_dest[2] = 51     'ASCII number for "3"
FAT_dest[3] = 13     'ASCII number for "CR"
FAT_dest[4] = 10     'ASCII number for "LF"
FAT_dest[5] = 51     'ASCII number for "3"
FAT_dest[6] = 55     'ASCII number for "7"
FAT_dest[7] = 13     'ASCII number for "CR"
FAT_dest[8] = 10     'ASCII number for "LF"
FAT_dest[9] = 57     'ASCII number for "9"
FAT_dest[10] = 50     'ASCII number for "2"

Then, you have to do some data manipulation to obtain the bytes that you need, 203, 37, and 92. This takes too much time . Is there any way or is there any format for my TXT file that I can use were I would obtain a SDFS reading like the following?

FAT_dest[0] = 203  
FAT_dest[1] = 37
FAT_dest[2] = 92

This would speed up my program a lot and I would obtain much better graphics in my TFT display. Thank you for your help.

Robert

[mackrackit]

I do not have a good answer at the moment. I mostly use SD card for logging and yes the FAT file system can be a bit slow.

How often is the display updated in your app?

[rsocor01]

........ and yes the FAT file system can be a bit slow.

So, is the FAT32 (SDFSHC32) much faster than FAT (SDFS3)? I didn't go for the FAT32 because it takes a lot of space in the chip.

The display changes whenever a new screen is selected and hopefully the transition should be smooth. What do you think would be the best way to read the data from the card the way I need it?

Robert

[mackrackit]

Can not say exactly but FAT32 should be a little slower, larger sectors to read I guess.

Can you have the data on the card in CSV format instead of line by line? Be a little less reading.

Might post your code, maybe someone will see something?

[rsocor01]

Can not say exactly but FAT32 should be a little slower, larger sectors to read I guess.

Good guess! I did some research in google and FAT32 is slower than FAT. I think that I found a solution to the problem I'm having, but I have to test it before I post it here.

My code is just the SDFS code, the EasyHID code, and the code to drive the TFT display all mixed together. I'm just testing everything together and so far my program is working fine.

Robert

[rsocor01]

mackrackit,

I probably found a way to speed up the process of writing to the TFT display. If you write bytes to the SD card with values from 0 to 255, which is what I need

' Write to file
FOR I = 0 TO 255
    FAT_src[0] = I
    FAT_count = 1
    Gosub FSfwrite
    Serout2 PORTC.6, 84, [ "Write ", Dec FAT_error, $d, $a]
    If (FAT_error != 0) Then Stop
NEXT I

The program will sucessfully write 256 bytes to the txt file (a bunch of weird characters ). Now, when you try to read them back, it will always give you wrong values between the byte 210th and the byte 250th. However, by using only 7 bits in every byte (from 0 to 127) I can make my display work pretty fast. Have you seen this happen to you? Any comments?

Now, for some strange reason my SD card is only working the first time after I reprogram the 18F4550 chip. The second time that I restart the chip I get the following errors for the FSinit

FAT_error = 6
SDC_status = 2 
SDC_response = 63

I know what the FAT_error = 6 is (Init error), but the others I'm not sure what they are. Have you encounter these kind of errors before? Remember, it always works right after I reprogram the MCU. Any ideas?

Thank you for all your help

Robert

[mackrackit]

Not sure about the writing problem.

The errors.
Open SDFS and about 70 lines down it has the errors listed. #2 is "card not present", #63 I do not see.

But, to get around the problem I have this in my "SDINIT" routine.

IF (FAT_error = 6) THEN SD_MAIN

Here is a snippet from my code template.

'###############################################
 SD_MAIN:
    TOGGLE PORTD.7
    GOSUB SDINIT
    GOSUB SDFILENAME
    GOSUB SDOPEN_W
    GOSUB SD_WRITE
    GOSUB SDCLOSE
 RETURN      '##############################################################
SDINIT:
' FSInit initializes the card and reads all the preliminary information from it
Gosub FSInit
Serout2 PORTC.6, 16572, ["Init: ", Dec FAT_error, " ", Dec SDC_status, " ", Dec SDC_response, $d, $a]
    IF (FAT_error = 6) THEN SD_MAIN
    If (FAT_error != 0) Then Stop
    ' Display card directory
    Gosub FINDfirst        ' Find first file on card
    While (FAT_error = 0)
        Serout2 PORTC.6,16572, [Str FAT_FileName\11, $d, $a]
        Gosub FINDnext    ' Find next file on card
    Wend
    RETURN
 '################################################################