From: Keith Packard <keithp@keithp.com>
Date: Wed, 14 May 2014 00:30:47 +0000 (-0700)
Subject: altos/cc1111: Wait for xtal to be stable
X-Git-Tag: 1.3.2.2~102
X-Git-Url: https://git.gag.com/?p=fw%2Faltos;a=commitdiff_plain;h=feb0b5f8b28767197f87e5818812d6640c1f40e6

altos/cc1111: Wait for xtal to be stable

Errata http://www.ti.com/lit/er/swrz022c/swrz022c.pdf says that the
xtal is stable bit is bogus and that you need to just delay for a while.

Signed-off-by: Keith Packard <keithp@keithp.com>
---

diff --git a/src/cc1111/ao_timer.c b/src/cc1111/ao_timer.c
index 75cc4ce8..d681f51b 100644
--- a/src/cc1111/ao_timer.c
+++ b/src/cc1111/ao_timer.c
@@ -83,25 +83,48 @@ ao_timer_init(void)
 	T1CTL = T1CTL_MODE_MODULO | T1CTL_DIV_8;
 }
 
+static void
+ao_clock_delay(void)
+{
+	uint16_t	i = 0;
+
+	while (--i)
+		ao_arch_nop();
+}
+
 /*
  * AltOS always cranks the clock to the max frequency
  */
 void
 ao_clock_init(void)
 {
-	/* Switch system clock to crystal oscilator */
-	CLKCON = (CLKCON & ~CLKCON_OSC_MASK) | (CLKCON_OSC_XTAL);
+	/* Power up both oscillators */
+	SLEEP &= ~(SLEEP_OSC_PD);
 
-	while (!(SLEEP & SLEEP_XOSC_STB))
+	/* Switch to the HFRC oscillator */
+	CLKCON = (CLKCON & ~CLKCON_OSC_MASK) | (CLKCON_OSC_RC);
+
+	/* Wait for the HFRC oscillator to be stable */
+	while (!(SLEEP & SLEEP_HFRC_STB))
 		;
 
+	/* Delay for 'a while' waiting for the crystal to
+	 * stabilize -- the XOSC_STB bit isn't reliable
+	 *
+	 *  http://www.ti.com/lit/er/swrz022c/swrz022c.pdf
+	 */
+
+	ao_clock_delay();
+
+	/* Switch system clock to crystal oscilator */
+	CLKCON = (CLKCON & ~CLKCON_OSC_MASK) | (CLKCON_OSC_XTAL);
+
 	/* Power down the unused HFRC oscillator */
 	SLEEP |= SLEEP_OSC_PD;
 
 	/* Wait for HFRC to power down */
 	while ((SLEEP & SLEEP_HFRC_STB) != 0)
 		;
-	
 	/* Crank up the timer tick and system clock speed */
 	CLKCON = ((CLKCON & ~(CLKCON_TICKSPD_MASK | CLKCON_CLKSPD_MASK)) |
 		  (CLKCON_TICKSPD_1 | CLKCON_CLKSPD_1));