Implement LP and us tickers to CM3DS

This commit represents the first stage of the low power implementations
that are required from Mbed 5.10 onwards. The LP ticker has been
implemented using a CMSDK Dual Timer's both timers (HW prescaler needed
to operate in the specified frequency domain), whereas the us ticker
uses one CMSDK Timer. Besides the default hal implementations (lp_ticker.c
and us_ticker.c), the CMSDK Dual Timer's native driver needed to be added.

Change-Id: I0b16b93dfac7753bebf430a2ce77761cb9c43ee5
Signed-off-by: Bence Kaposzta <[email protected]>

Author: kapi90

targets/TARGET_ARM_SSG/TARGET_CM3DS_MPS2/device/device_cfg.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018 ARM Limited
+ * Copyright (c) 2018 Arm Limited
  *
  * Licensed under the Apache License Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -27,8 +27,50 @@
  */
 
 /* CMSDK Timers */
-#define ARM_CMSDK_TIMER0
 #define ARM_CMSDK_TIMER1
+#define ARM_CMSDK_DUALTIMER
+
+/* Timer Peripherals are driven by APB System Core Clocks,
+ * defined in system_CMSDK_CM3DS.c
+ */
+#define TIMERS_INPUT_CLOCK_FREQ_HZ       25000000U
+
+/* mbed usec high-resolution ticker configuration */
+#define USEC_TIMER_DEV                   CMSDK_TIMER1_DEV
+
+#define usec_interval_irq_handler        TIMER1_IRQHandler
+#define USEC_INTERVAL_IRQ                TIMER1_IRQn
+
+/* The us ticker uses CMSDK Timer1, that does not have HW prescaler.
+ * The reported shift define is necessary for the software emulated
+ * prescaler behavior, so the ticker works as if it was ticking on a
+ * virtually slower frequency. The value 5 sets up the ticker to work
+ * properly in the specified frequency interval.
+ */
+#define USEC_TIMER_BIT_WIDTH    32U
+#define USEC_REPORTED_SHIFT     5U
+#define USEC_REPORTED_FREQ_HZ   (TIMERS_INPUT_CLOCK_FREQ_HZ >> USEC_REPORTED_SHIFT)
+#define USEC_REPORTED_BITS      (USEC_TIMER_BIT_WIDTH - USEC_REPORTED_SHIFT)
+
+/* mbed low power ticker configuration */
+#define LP_TIMER_DEV                     CMSDK_DUALTIMER_DEV
+
+#define lp_interval_irq_handler          DUALTIMER_IRQHandler
+#define LP_INTERVAL_IRQ                  DUALTIMER_IRQn
+
+/* The lp ticker a CMSDK Dual Timer that is capable of prescaling
+ * its input clock frequency by 256 at most. Having 25MHz as input
+ * frequency requires an additional slowing factor in order for the ticker
+ * to operate in the specified frequency interval, thus the effective
+ * prescaler value is going to be the sum of the HW and the virtual
+ * prescaler values.
+ */
+#define LP_TIMER_BIT_WIDTH            32U
+#define LP_TIMER_HW_PRESCALER         8U
+#define LP_REPORTED_SHIFT             1U
+#define LP_REPORTED_FREQ_HZ           (TIMERS_INPUT_CLOCK_FREQ_HZ >> \
+                                      (LP_TIMER_HW_PRESCALER+LP_REPORTED_SHIFT))
+#define LP_REPORTED_BITS              (LP_TIMER_BIT_WIDTH - LP_REPORTED_SHIFT)
 
 /* ARM GPIO */
 #define ARM_GPIO0
@@ -51,7 +93,7 @@
 #define ARM_SPI4
 
 /* ARM UART */
-#define DEFAULT_UART_BAUDRATE  9600
+#define DEFAULT_UART_BAUDRATE  9600U
 #define ARM_UART0
 #define ARM_UART1
 #define ARM_UART2