diff --git a/sys/dev/iicbus/nxprtc.c b/sys/dev/iicbus/nxprtc.c
index 37976a664c69..02eb9f85b513 100644
--- a/sys/dev/iicbus/nxprtc.c
+++ b/sys/dev/iicbus/nxprtc.c
@@ -33,8 +33,8 @@ __FBSDID("$FreeBSD$");
  *  - PCA8565 = like PCF8563, automotive temperature range
  *  - PCF8523 = low power, countdown timer, oscillator freq tuning, 2 timers
  *  - PCF2127 = like PCF8523, industrial, tcxo, tamper/ts, i2c & spi, 512B ram
- *  - PCA2129 = like PCF8523, automotive, tcxo, tamper/ts, i2c & spi, no timer
- *  - PCF2129 = like PCF8523, industrial, tcxo, tamper/ts, i2c & spi, no timer
+ *  - PCA2129 = like PCF8523, automotive, tcxo, tamper/ts, i2c & spi, (note 1)
+ *  - PCF2129 = like PCF8523, industrial, tcxo, tamper/ts, i2c & spi, (note 1)
  *
  *  Most chips have a countdown timer, ostensibly intended to generate periodic
  *  interrupt signals on an output pin.  The timer is driven from the same
@@ -42,6 +42,13 @@ __FBSDID("$FreeBSD$");
  *  in sync when the STOP bit is cleared after the time and timer registers are
  *  set.  The timer register can also be read on the fly, so we use it to count
  *  fractional seconds and get a resolution of ~15ms.
+ *
+ *  [1] Note that the datasheets for the PCx2129 chips state that they have only
+ *  a watchdog timer, not a countdown timer.  Empirical testing shows that the
+ *  countdown timer is actually there and it works fine, except that it can't
+ *  trigger an interrupt or toggle an output pin like it can on other chips.  We
+ *  don't care about interrupts and output pins, we just read the timer register
+ *  to get better resolution.
  */
 
 #include "opt_platform.h"
@@ -471,7 +478,13 @@ pcf2127_start_timer(struct nxprtc_softc *sc)
 	int err;
 	uint8_t stdctl, tmrctl;
 
-	/* See comment in pcf8523_start_timer().  */
+	/*
+	 * Set up timer if it's not already in the mode we normally run it.  See
+	 * the comment in pcf8523_start_timer() for more details.
+	 *
+	 * Note that the PCF2129 datasheet says it has no countdown timer, but
+	 * empirical testing shows that it works just fine for our purposes.
+	 */
 	if ((err = read_reg(sc, PCF2127_R_TMR_CTL, &tmrctl)) != 0)
 		return (err);
 
@@ -521,10 +534,6 @@ nxprtc_start(void *dev)
 	switch (sc->chiptype) {
 	case TYPE_PCA2129:
 	case TYPE_PCF2129:
-		if (pcf8523_start(sc) != 0)
-			return;
-		/* No timer to start */
-		break;
 	case TYPE_PCF2127:
 		if (pcf8523_start(sc) != 0)
 			return;
@@ -796,10 +805,6 @@ nxprtc_attach(device_t dev)
 	switch (sc->chiptype) {
 	case TYPE_PCA2129:
 	case TYPE_PCF2129:
-		sc->secaddr = PCF8523_R_SECOND;
-		sc->tmcaddr = 0;
-		sc->use_timer = false;
-		break;
 	case TYPE_PCF2127:
 	case TYPE_PCF8523:
 		sc->secaddr = PCF8523_R_SECOND;