only limited bytes of data is being read through f_read in fpga

Question

I am running a code in zybo board (through vitis SDK) that reads .csv file from external SD card and stores it in local variable for further processing. I am using f_read function to read the file.

I am able to read the file but the problem is it is reading only 0x38000 bytes of data whereas file contains more than that. I increased my stack and heap memory as well.

void readImageFile(double**** array){
int a=0,b=0,c=0,d=0;
char *line=NULL; // for reading every line of input file.
char *value= NULL; // for every point in one sample1 line (178 points in 1 line)
FIL test_data_inputs_pointer;
FRESULT result =  f_open(&test_data_inputs_pointer, "0:/images.csv", FA_READ);
u32 file_size = (227*68100*4);
UINT NumBytesRead;
char *DestinationAddress;
int lineNo=0;
FRESULT read_result = f_read (&test_data_inputs_pointer, (void*)DestinationAddress, file_size, &NumBytesRead);

In debugging mode, variable NumBytesRead has value of 0x38000.