Re: [Xbox-linux-user] Writing to XPad memory unit

--- Lunpa <[email protected]> wrote:

> nifty.
> how is it used?
> 
> 

Like this:

  $ uudecode email.txt
  $ gzip -d xpad-write.gz
  $ chmod +x xpad-write
  $ ./xpad-write
  usage: xpad-write image_file
  $ MCARD=/dev/sdb ./xpad-write image.bin

MCARD defaults to '/dev/sda'.

==============
Why this works
==============

It looks like the memory unit must be written to in 8k blocks, or multiples 
thereof.  Even so, the following code does not work:

  for (i = 0; i < 1008; i++)
          write(fd, buf, 8192);

The SCSI driver seems to buffer writes, and send off write commands to the 
lower-level driver with buffer sizes it sees fit.  For example, the above 
code produces 127k writes to the USB storage driver on my laptop.  Below are 
the first nine ranges of un-corrupted 1k blocks for the above code:

     0 -  120
   127 -  248
   254 -  376
   381 -  504
   508 -  632
   635 -  760
   762 -  888
   889 - 1136 *
  1143 - 1264
  ...

Notice that the eighth block written had no corrupted blocks at the end 
since it ended on an 8k boundry.

So, if instead of the above code I run the following:

  for (i = 0; i < 1008; i++) {
          fd = open("/dev/sda", O_RDWR);
          lseek(fd, i*8192, SEEK_SET);
          write(fd, buf, 8192);
          close(fd);
  }

I now get un-corrupted writes out to the memory unit.  Opening/closing the 
file each time forces individual SCSI commands to be sent to the USB device 
for each 8k write.  Presumably, this would work for a buffer size of 16k, 
32k, etc.  So, now it is more obvious why my script using dd to write one 8k 
block at a time worked!

I'm not familiar enough with the SCSI or USB kernel code to know immediately 
how to fix this, but I would think this should be an easy fix.  Any ideas?

Thanks,

Chris Rorvick


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