staging: comedi: das1800: clarify the analog input cmd triggers

Clarify the documentation in the comedi driver comment block to
better explain the cmd triggert.

Add a comment to step 2b of the (*do_cmdtest) to clarify the
trigger check.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/comedi/drivers/das1800.c b/drivers/staging/comedi/drivers/das1800.c
index 9153c9b..bfbc2bb 100644 (file)
--- a/drivers/staging/comedi/drivers/das1800.c
+++ b/drivers/staging/comedi/drivers/das1800.c
@@ -39,19 +39,32 @@
  *   [3] - DMA1 (optional, requires irq and dma0)
  *
  * analog input cmd triggers supported:
- *   start_src:                TRIG_NOW | TRIG_EXT
- *   scan_begin_src:   TRIG_FOLLOW | TRIG_TIMER | TRIG_EXT
- *   scan_end_src:     TRIG_COUNT
- *   convert_src:      TRIG_TIMER | TRIG_EXT
- *                     (TRIG_EXT requires scan_begin_src == TRIG_FOLLOW)
- *   stop_src:         TRIG_COUNT | TRIG_EXT | TRIG_NONE
  *
- * scan_begin_src triggers TRIG_TIMER and TRIG_EXT use the card's
- * 'burst mode' which limits the valid conversion time to 64 microseconds
- * (convert_arg <= 64000). This limitation does not apply if scan_begin_src
- * is TRIG_FOLLOW.
+ *   start_src         TRIG_NOW        command starts immediately
+ *                     TRIG_EXT        command starts on external pin TGIN
  *
- * The maximum conversion speeds are not always achievable depending on the
+ *   scan_begin_src    TRIG_FOLLOW     paced/external scans start immediately
+ *                     TRIG_TIMER      burst scans start periodically
+ *                     TRIG_EXT        burst scans start on external pin XPCLK
+ *
+ *   scan_end_src      TRIG_COUNT      scan ends after last channel
+ *
+ *   convert_src       TRIG_TIMER      paced/burst conversions are timed
+ *                     TRIG_EXT        conversions on external pin XPCLK
+ *                                     (requires scan_begin_src == TRIG_FOLLOW)
+ *
+ *   stop_src          TRIG_COUNT      command stops after stop_arg scans
+ *                     TRIG_EXT        command stops on external pin TGIN
+ *                     TRIG_NONE       command runs until canceled
+ *
+ * If TRIG_EXT is used for both the start_src and stop_src, the first TGIN
+ * trigger starts the command, and the second trigger will stop it. If only
+ * one is TRIG_EXT, the first trigger will either stop or start the command.
+ *
+ * Minimum conversion speed is limited to 64 microseconds (convert_arg <= 64000)
+ * for 'burst' scans. This limitation does not apply for 'paced' scans. The
+ * maximum conversion speed is limited by the board (convert_arg >= ai_speed).
+ * Maximum conversion speeds are not always achievable depending on the
  * board setup (see user manual).
  *
  * NOTES:
@@ -653,6 +666,7 @@ static int das1800_ai_cmdtest(struct comedi_device *dev,
 
        /* Step 2b : and mutually compatible */
 
+       /* burst scans must use timed conversions */
        if (cmd->scan_begin_src != TRIG_FOLLOW &&
            cmd->convert_src != TRIG_TIMER)
                err |= -EINVAL;