add examples

RTL00_SDKV35a/example_sources/pm_tickless/readme.txt

@@ -0,0 +1,31 @@
+Example Description
+
+This example describes how to use freertos tickless with uart interruptable interface
+
+Requirement Components:
+	USBtoTTL adapter
+
+Connect to PC
+ - Connect Ground: connect to GND pin via USBtoTTL adapter
+ - Use UART1
+	GPIOA_0 as UART1_RX connect to TX of USBtoTTL adapter
+	GPIOA_4 as UART1_TX connect to RX of USBtoTTL adapter
+
+We also need connect GPIOC_1 as gpio interrupt which parallel with log uart rx pin.
+
+In this example, freertos will enter/leave tickless automatically.
+User can type continuous "Enter" in uart or log uart to wake system if system is in tickless.
+System is keep awake until user type a command via uart.
+
+There are some features in this example:
+(1) We replace tickless' sleep function with system sleep api which save more power.
+(2) Freertos enter tickless if the wakelock bit map is 0.
+    It means there is no function require system keep awake.
+    By default there is WAKELOCK_OS keep system awake.
+    So we need release this WAKELOCK_OS enable tickless mode.
+(3) We configure uart rx as gpio interrupt mode. This make uart can wake system.
+
+NOTICE: If you don't want loss any data from treating UART signal as GPIO interrupt,
+        you can set FREERTOS_PMU_TICKLESS_PLL_RESERVED to 1 in "platform_opt.h".
+        It will reserved PLL clock in tickless and UART can receive the whole data.
+        But it also cost more power consumption.