Cr50: Enable the USB SOF clock auto-calibrationstabilize-8282.B

The timer clock nominally requires no firmware settings. It is
tuned in manufacturing to be centered around 24MHz. However, it
will potentially migrate away from 24MHz based upon variations in
temperature and voltage. The variation is approximately
0.1-0.5MHz, based upon functional simulations, and backed up with
observations in the lab. This CL enables a hardware feature to
dynamically tune the timer clock if the device has an active USB
port, by monitoring the SOF (start of frame) USB packets that are
sent by the USB host every milllsecond with 500ppm accuracy.

BUG=chrome-os-partner:50800
BRANCH=none
TEST=make buildall; run on Cr50 hardware

Verified that deep sleep, USB suspend/resume, etc continue to
work with this enabled. Not too surprising, since I've never
encountered a problem without it.

In addition, I monitored XO_CLK_TIMER_CURRENT to see that the
timer adjustments are being made while connecting and
disconnecting from USB, entering andleaving sleep and deep sleep,
etc. They are.

Change-Id: I328b6416bc40ef8718815c5e09cf91ec1c6646f0
Signed-off-by: Bill Richardson <wfrichar@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/342145
Reviewed-by: Vadim Bendebury <vbendeb@chromium.org>

1 files changed, 4 insertions, 2 deletions

diff --git a/chip/g/usb.c b/chip/g/usb.c
index b5e036d60b..d47912dd02 100644
--- a/chip/g/usb.c
+++ b/chip/g/usb.c
@@ -9,6 +9,7 @@
 #include "console.h"
 #include "gpio.h"
 #include "hooks.h"
+#include "init_chip.h"
 #include "link_defs.h"
 #include "registers.h"
 #include "system.h"
@@ -1073,6 +1074,9 @@ static void usb_reset(void)
 
 	/* Reinitialize all the endpoints */
 	usb_init_endpoints();
+
+	/* Init the clock calibrator */
+	init_sof_clock();
 }
 
 static void usb_resetdet(void)
@@ -1188,14 +1192,12 @@ static void usb_softreset(void)
 
 void usb_connect(void)
 {
-	CPRINTS("%s", __func__);
 	print_later("usb_connect()", 0, 0, 0, 0, 0);
 	GR_USB_DCTL &= ~DCTL_SFTDISCON;
 }
 
 void usb_disconnect(void)
 {
-	CPRINTS("%s", __func__);
 	print_later("usb_disconnect()", 0, 0, 0, 0, 0);
 	GR_USB_DCTL |= DCTL_SFTDISCON;