svn commit: r354180 - head/sys/dev/ow

[Andriy Gapon]

Author: avg
Date: Wed Oct 30 15:15:53 2019
New Revision: 354180
URL: https://svnweb.freebsd.org/changeset/base/354180

Log:
  ow(4): increase regular mode recovery time, t_rec, to 15 us
  
  Previously we used the minimal value of 1 us and it was really tight.
  Application Note 3829 has a table describing recommended t_rec values
  for various bus voltages, temperature conditions and numbers of slave
  devices.  The new value decreases the maximum possible data rate from
  16.3 Kbit/s to 13.3 Kbit/s, but it allows for up to four slaves on a
  3.3V bus (under room temperature).
  
  References:
  - Maxim Integrated Application Note 3829
    Determining the Recovery Time for Multiple-Slave 1-Wire(R) Networks
  
  - Maxim Integrated Application Note 937
    Book of iButton Standards
  
  Discussed with:	imp (D22108)
  MFC after:	3 weeks

Modified:
  head/sys/dev/ow/ow.c

Modified: head/sys/dev/ow/ow.c
==============================================================================
--- head/sys/dev/ow/ow.c	Wed Oct 30 14:05:50 2019	(r354179)
+++ head/sys/dev/ow/ow.c	Wed Oct 30 15:15:53 2019	(r354180)
@@ -80,7 +80,7 @@ static struct ow_timing timing_regular = {
 	.t_low0 = 60,		/* really 60 to 120 */
 	.t_low1 = 1,		/* really 1 to 15 */
 	.t_release = 45,	/* <= 45us */
-	.t_rec = 1,		/* at least 1us */
+	.t_rec = 15,		/* at least 1us */
 	.t_rdv = 15,		/* 15us */
 	.t_rstl = 480,		/* 480us or more */
 	.t_rsth = 480,		/* 480us or more */