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 */
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