Copy edit rtos.md

Copy edit file for minor grammar nits, such as sentence case in headings and precise language.

Author: Amanda Butler

docs/reference/api/rtos/rtos.md

@@ -1,17 +1,17 @@
 <h2 id="rtos-api">RTOS overview</h2>
 
-The Mbed OS RTOS provides C++ APIs to manage objects like threads, synchronization objects, and timers. It also provides interfaces for attaching application specific idle hook function, read the OS tick count and implements functionality to report RTOS errors.
+The Mbed OS RTOS provides C++ APIs to manage objects such as threads, synchronization objects and timers. It also provides interfaces for attaching an application-specific idle hook function, reads the OS tick count and implements functionality to report RTOS errors.
 
 The code of the Mbed RTOS can be found in the [`mbed-os`](https://github.com/ARMmbed/mbed-os) repository, in the [RTOS subdirectory](https://github.com/ARMmbed/mbed-os/tree/master/rtos). See [the Doxygen](https://os-doc-builder.test.mbed.com/docs/development/mbed-os-api-doxy/group__rtos.html) for more information.
 
 #### RTOS Ticker
-Platforms using RTOS, including Mbed OS, need a mechanism for counting the time and scheduling tasks. This is usually done by a timer which generates periodic interrupts and is called system tick timer. 
-Under Mbed OS, we call this mechanism RTOS ticker.
+
+Platforms using RTOS, including Mbed OS, need a mechanism for counting the time and scheduling tasks. A timer that generates periodic interrupts and is called system tick timer usually does this. Under Mbed OS, we call this mechanism the RTOS ticker.
 
 SysTick is a standard timer available on most Cortex-M cores. Its main purpose is to raise an interrupt with set frequency (usually 1ms). In addition, many Mbed OS platforms 
 implement timers as part of peripherals. Mbed OS supports using SysTick or the peripheral timers as RTOS ticker.
 
-Mbed OS platforms uses SysTick as the default RTOS ticker, but if you want to use one of the peripheral timers as your RTOS ticker you can do so by overriding the default SysTick timer. For example, see [Low Power Ticker](/docs/development/reference/low-power-ticker.html) on how to use external low power timer to perform power efficient timing operations that only requires millisecond accuracy.
+The Mbed OS platforms uses SysTick as the default RTOS ticker, but if you want to use one of the peripheral timers as your RTOS ticker, you can override the default SysTick timer. For example, see [Low Power Ticker](/docs/development/reference/low-power-ticker.html) on how to use an external low power timer to perform power efficient timing operations that only require millisecond accuracy.
 
 #### RTOS APIs
 
@@ -24,10 +24,10 @@ The RTOS APIs handle creation and destruction of threads in Arm Mbed OS 5, as we
 - [MemoryPool](/docs/development/reference/memorypool.html): This class that you can use to define and manage fixed-size memory pools
 - [Mail](/docs/development/reference/mail.html): The API that provides a queue combined with a memory pool for allocating messages.
 - [RtosTimer](/docs/development/reference/rtostimer.html): A deprecated class used to control timer functions in the system.
-- [EventFlags](/docs/development/reference/eventflags.html): An event channel that provides a generic way of notifying other threads about conditions or events. Some EventFlags functions are callable from ISR context and each EventFlags objects can support up to 31 flags.
+- [EventFlags](/docs/development/reference/eventflags.html): An event channel that provides a generic way of notifying other threads about conditions or events. You can call some EventFlags functions from ISR context, and each EventFlags object can support up to 31 flags.
 - [Event](/docs/development/reference/event.html): The queue to store events, extract them and excute them later.
-- [ConditionVariable](/docs/development/reference/conditionvariable.html): The ConditionVariable class provides a mechanism to safely wait for or signal a single state change. ConditionVariable functions are not callable from ISR context.
-- [Kernel](/docs/development/reference/kernel.html): Kernel namespace implements functions to control or read RTOS information like tick count.
+- [ConditionVariable](/docs/development/reference/conditionvariable.html): The ConditionVariable class provides a mechanism to safely wait for or signal a single state change. You cannot call ConditionVariable functions from ISR context.
+- [Kernel](/docs/development/reference/kernel.html): Kernel namespace implements functions to control or read RTOS information, such as tick count.
 
 ##### Default timeouts
 
@@ -56,6 +56,6 @@ Each `Thread` can wait for signals and be notified of events:
 
 [![View code](https://www.mbed.com/embed/?url=https://os.mbed.com/teams/mbed_example/code/rtos_signals/)](https://os.mbed.com/teams/mbed_example/code/rtos_signals/file/476186ff82cf/main.cpp)
 
-##### Status and Error codes
-Mbed OS error handling system assigns specific error codes for RTOS related erros. See [Error Handling](/docs/development/reference/error-handling.html)
-for more information on RTOS errors reported.
+##### Status and error codes
+
+The Mbed OS error handling system assigns specific error codes for RTOS-related erros. See [the error handling documentation](/docs/development/reference/error-handling.html) for more information on RTOS errors reported.