try to fix problems on pc104-das16jr that occur when an

dma transfer with an odd number of bytes occurs.

diff --git a/comedi/drivers/das16.c b/comedi/drivers/das16.c
index d211d10e7bd1b288faaf634f20641edf400f2f89..ba4f894d0357e765aad91f0b42dc53711968792a 100644 (file)
--- a/comedi/drivers/das16.c
+++ b/comedi/drivers/das16.c
@@ -1171,6 +1171,41 @@ static void das16_timer_interrupt(unsigned long arg)
                mod_timer(&devpriv->timer, jiffies + timer_period());
 }
 
+/* the pc104-das16jr (at least) has problems if the dma
+       transfer is interrupted in the middle of transferring
+       a 16 bit sample, so this function takes care to get
+       an even transfer count after disabling dma
+       channel.
+*/
+static int disable_dma_on_even(comedi_device *dev)
+{
+       int residue;
+       int i;
+       static const int disable_limit = 100;
+       static const int enable_timeout = 100;
+       disable_dma(devpriv->dma_chan);
+       residue = get_dma_residue(devpriv->dma_chan);
+       for(i = 0; i < disable_limit && (residue % 2); ++i)
+       {
+               int j;
+               enable_dma(devpriv->dma_chan);
+               for(j = 0; j < enable_timeout; ++j)
+               {
+                       int new_residue;
+                       comedi_udelay(2);
+                       new_residue = get_dma_residue(devpriv->dma_chan);
+                       if(new_residue != residue) break;
+               }
+               disable_dma(devpriv->dma_chan);
+               residue = get_dma_residue(devpriv->dma_chan);
+       }
+       if(i == disable_limit)
+       {
+               comedi_error(dev, "failed to get an even dma transfer, could be trouble.");
+       }
+       return residue;
+}
+
 static void das16_interrupt( comedi_device *dev )
 {
        unsigned long dma_flags, spin_flags;
@@ -1204,17 +1239,10 @@ static void das16_interrupt( comedi_device *dev )
        }
 
        dma_flags = claim_dma_lock();
-       disable_dma(devpriv->dma_chan);
-       /* clear flip-flop to make sure 2-byte registers for
-        * count and address get set correctly */
        clear_dma_ff(devpriv->dma_chan);
+       residue = disable_dma_on_even(dev);
 
        // figure out how many points to read
-
-       /* residue is the number of bytes left to be done on the dma
-        * transfer.
-        */
-       residue = get_dma_residue(devpriv->dma_chan);
        if(residue > devpriv->dma_transfer_size)
        {
                comedi_error(dev, "residue > transfer size!\n");