From b35050917272ab536c8f4158e5c002f98a092796 Mon Sep 17 00:00:00 2001
From: Amar Takhar <amar@rtems.org>
Date: Sun, 17 Jan 2016 00:47:50 -0500
Subject: Split document into seperate files by section.

---
 bsp_howto/timer.rst | 104 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 104 insertions(+)
 create mode 100644 bsp_howto/timer.rst

(limited to 'bsp_howto/timer.rst')

diff --git a/bsp_howto/timer.rst b/bsp_howto/timer.rst
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+Timer Driver
+############
+
+The timer driver is primarily used by the RTEMS Timing Tests.
+This driver provides as accurate a benchmark timer as possible.
+It typically reports its time in microseconds, CPU cycles, or
+bus cycles.  This information can be very useful for determining
+precisely what pieces of code require optimization and to measure the
+impact of specific minor changes.
+
+The gen68340 BSP also uses the Timer Driver to support a high performance
+mode of the on-CPU UART.
+
+Benchmark Timer
+===============
+
+The RTEMS Timing Test Suite requires a benchmark timer.  The
+RTEMS Timing Test Suite is very helpful for determining
+the performance of target hardware and comparing its performance
+to that of other RTEMS targets.
+
+This section describes the routines which are assumed to exist by
+the RTEMS Timing Test Suite.  The names used are *EXACTLY* what
+is used in the RTEMS Timing Test Suite so follow the naming convention.
+
+benchmark_timer_initialize
+--------------------------
+
+Initialize the timer source.
+.. code:: c
+
+    void benchmark_timer_initialize(void)
+    {
+    initialize the benchmark timer
+    }
+
+Read_timer
+----------
+
+The ``benchmark_timer_read`` routine returns the number of benchmark
+time units (typically microseconds) that have elapsed since the last
+call to ``benchmark_timer_initialize``.
+.. code:: c
+
+    benchmark_timer_t benchmark_timer_read(void)
+    {
+    stop time = read the hardware timer
+    if the subtract overhead feature is enabled
+    subtract overhead from stop time
+    return the stop time
+    }
+
+Many implementations of this routine subtract the overhead required
+to initialize and read the benchmark timer.  This makes the times reported
+more accurate.
+
+Some implementations report 0 if the harware timer value change is
+sufficiently small.  This is intended to indicate that the execution time
+is below the resolution of the timer.
+
+benchmark_timer_disable_subtracting_average_overhead
+----------------------------------------------------
+
+This routine is invoked by the "Check Timer" (``tmck``) test in the
+RTEMS Timing Test Suite.  It makes the ``benchmark_timer_read``
+routine NOT subtract the overhead required
+to initialize and read the benchmark timer.  This is used
+by the ``tmoverhd`` test to determine the overhead
+required to initialize and read the timer.
+.. code:: c
+
+    void benchmark_timer_disable_subtracting_average_overhead(bool find_flag)
+    {
+    disable the subtract overhead feature
+    }
+
+The ``benchmark_timer_find_average_overhead`` variable is used to
+indicate the state of the "subtract overhead feature".
+
+gen68340 UART FIFO Full Mode
+============================
+
+The gen68340 BSP is an example of the use of the timer to support the UART
+input FIFO full mode (FIFO means First In First Out and roughly means
+buffer). This mode consists in the UART raising an interrupt when n
+characters have been received (*n* is the UART’s FIFO length). It results
+in a lower interrupt processing time, but the problem is that a scanf
+primitive will block on a receipt of less than *n* characters. The solution
+is to set a timer that will check whether there are some characters
+waiting in the UART’s input FIFO. The delay time has to be set carefully
+otherwise high rates will be broken:
+
+- if no character was received last time the interrupt subroutine was
+  entered, set a long delay,
+
+- otherwise set the delay to the delay needed for *n* characters
+  receipt.
+
+.. COMMENT: COPYRIGHT (c) 1988-2002.
+
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+
+.. COMMENT: All rights reserved.
+
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