Merge pull request #4 from dhalbert/lengthen-xosc-startup

Allow much more time for xosc to start

src/rp2_common/hardware_xosc/xosc.c

@@ -13,14 +13,17 @@
 #include "hardware/regs/xosc.h"
 #include "hardware/structs/xosc.h"
 
+#define XOSC_STARTUP_DELAY_MULTIPLIER (64)
+
 void xosc_init(void) {
     // Assumes 1-15 MHz input
     assert(XOSC_MHZ <= 15);
     xosc_hw->ctrl = XOSC_CTRL_FREQ_RANGE_VALUE_1_15MHZ;
 
     // Set xosc startup delay
     uint32_t startup_delay = (((12 * MHZ) / 1000) + 128) / 256;
-    xosc_hw->startup = startup_delay;
+    // Lengthen startup delay to accomodate slow-starting oscillators
+    xosc_hw->startup = startup_delay * XOSC_STARTUP_DELAY_MULTIPLIER;
 
     // Set the enable bit now that we have set freq range and startup delay
     hw_set_bits(&xosc_hw->ctrl, XOSC_CTRL_ENABLE_VALUE_ENABLE << XOSC_CTRL_ENABLE_LSB);
@@ -43,4 +46,4 @@ void xosc_dormant(void) {
     xosc_hw->dormant = XOSC_DORMANT_VALUE_DORMANT;
     // Wait for it to become stable once woken up
     while(!(xosc_hw->status & XOSC_STATUS_STABLE_BITS));
-}
+}