Hi,

I write on usb mass storage with fwrite, and I have questions :

1.What is the buffer size of fwrite function ?

2.How write without buffer ? I want a POSIX write like function.

3.In the class MSCFileSystem, disk_sync isn't implemented. How request the key about the state of is buffer ? FATFileSystem has it a buffer ?

Thank you very much, and sorry for my bad english.

Steph.

Are you seeing issues with the data not getting saved out immediately when you write data to a file?

1) In section 2.4 of ARM document DUI 0475C - Using ARM® C and C++ Libraries and Floating-Point Support it mentions that a 512 byte buffer is associated with each file.

2) You should be able to use the setvbuf() API to remove the buffer if that is what you want.

3) I don't know the answer to this but you might want to try the setvbuf() trick first.

Sample usage of setvbuf()

#include "mbed.h"

LocalFileSystem local("local");

int main() 
{
    static const char SampleString[] = "Hello World\n";
    
    FILE* fp = fopen("/local/out.txt", "w");
    
    // If you issue this call right after the fopen then a buffer will never be allocated for the FILE
    setvbuf(fp, NULL, _IONBF, 0);
    
    fwrite(SampleString, strlen(SampleString), 1, fp);
    
    fclose(fp);
}

Thank you for this response.

Sorry, but I can't do blank line. It's a bug of this forum ?

512 byte is coherent with my result. And setvbuff solve a part of my problem :).

-

MSCFileSystem has only two fonction available for FATFileSystem : disk_read and disk_write. The two function read and write one bloc(512 bytes) of the USB Key.

When I use this function directly, to write a large set of data, I can write 512 times 512 bytes(256kB), and after writing fail. The result of disk_write is alwais the same (successful).

May be the key has 256kB of buffer ?

How FAT Filesystem know when he can write ? MSCFileSystem has no function for this.

-

NB : opening the source code of mbed library is very important for user. It's still planed ?

Do you have some code that you could share which shows the problem you are seeing?

I resolve my problem. I did a stupid mistake in my code ;).

My code is (WARNING : this code ERASE the filesystem on key !) :

char buff[512];
#define NBMESURE 1000
unsigned int mesure[NBMESURE];

void main()
{
    // Timer is configured to count all 1us.
    // PR was calibrated with oscilloscope.
    LPC_TIM0->TCR |= 0x03;
    LPC_SC->PCONP |= 0x02; 
    LPC_SC->PCLKSEL0= (LPC_SC->PCLKSEL0 & ~(0x03 << 2)) | (TIMER_DIVIDE << 2);
    LPC_TIM0->PR = 95;
    LPC_TIM0->TCR &= ~0x02;

    massStorage.disk_initialize();
    
    // place des données dans le buffer
    for(unsigned int i=0;i<512;i++)
    {
        buff[i]=0xAB;
    }    

    wait_ms(5000); // Because disk_initialize is async.

    TimeMesure[0]=LPC_TIM0->TC;
    for(i=1;i<64*NBMESURE;i++) 
    {
        if(massStorage.disk_write(buff,i))
        {
            printf("ERROR in bloc %d\n",i);
            while(1);
        }
        if(i%64 == 0)
            TimeMesure[i/64] = LPC_TIM0->TC;
        
        //TimeMesure[i]=LPC_TIM0->TC;
    }
    
    // Flushing data in buffer.
    wait(10);

    printf("Result :\n");
    printf("Starting bloc;Times\n");
    for(unsigned int i=0;i<1000-1;i++)
    {
        printf("%u;%u\n",i*64,TimeMesure[i+1]-TimeMesure[i]);
    }
    while(1);
}

The key write the data at less than 100ko/s. It's very bad, and I don't understand the reason. Do you have idea ?