------------------------------------------------------------------------------
-- --
-- GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS --
-- --
-- S Y S T E M . B B . B O A R D _ P A R A M E T E R S --
-- --
-- S p e c --
-- --
-- Copyright (C) 2016-2020, AdaCore --
-- --
-- GNAT is free software; you can redistribute it and/or modify it under --
-- terms of the GNU General Public License as published by the Free Soft- --
-- ware Foundation; either version 3, or (at your option) any later ver- --
-- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
-- or FITNESS FOR A PARTICULAR PURPOSE. --
-- --
-- As a special exception under Section 7 of GPL version 3, you are granted --
-- additional permissions described in the GCC Runtime Library Exception, --
-- version 3.1, as published by the Free Software Foundation. --
-- --
-- You should have received a copy of the GNU General Public License and --
-- a copy of the GCC Runtime Library Exception along with this program; --
-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
-- <http://www.gnu.org/licenses/>. --
-- --
-- GNAT was originally developed by the GNAT team at New York University. --
-- Extensive contributions were provided by Ada Core Technologies Inc. --
-- --
-- The port of GNARL to bare board targets was initially developed by the --
-- Real-Time Systems Group at the Technical University of Madrid. --
-- --
------------------------------------------------------------------------------
-- This package defines board parameters for the nRF52840-DK board
package System.BB.Board_Parameters is
pragma No_Elaboration_Code_All;
pragma Pure;
--------------------
-- Hardware clock --
--------------------
RTC_Tick_Scaling_Factor : constant := 32; -- 32.768 kHz * 32 = 1.048576 MHz
-- Use a fairly high scaling factor so that Ada.Real_Time.Time_Unit is
-- at least 1 microsecond. This improves the long-running accuracy of
-- periodic tasks where the period is not integer divisible by 32.768 kHz.
--
-- The maximum permitted scaling factor is 255, otherwise the 24-bit RTC
-- period (@ 32 kHz) cannot be scaled to the 32-bit range of
-- Timer_Interval.
Main_Clock_Frequency : constant := 32_768 * RTC_Tick_Scaling_Factor;
-- On the nRF52 we use the RTC peripheral as the system tick, instead of
-- the Cortex-M4 SysTick because the SysTick is powered down when the CPU
-- enters sleep mode (via the "wfi" instruction). Since we still want to
-- be able to put the CPU to sleep (to save power) we instead use the
-- low-power RTC peripheral, which runs at 32.768 kHz.
--
-- In this runtime, the minimum allowed frequency is 50_000 Hz so that
-- Ada.Real_Time.Time_Unit does not exceed 20 us as required by
-- Ada RM D.8 (30). Since the RTC's actual period is 30.518 us we multiply
-- the RTC frequency by RTC_Tick_Scaling_Factor so that Time_Unit meets the
-- requirement in Ada RM D.8 (30).
end System.BB.Board_Parameters;