rockbox/firmware/target/arm/as3525/system-target.h

/***************************************************************************
 *             __________               __   ___.
 *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
 *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
 *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
 *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
 *                     \/            \/     \/    \/            \/
 * $Id$
 *
 * Copyright (C) 2008 Rafaël Carré
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
 * KIND, either express or implied.
 *
 ****************************************************************************/
#ifndef SYSTEM_TARGET_H
#define SYSTEM_TARGET_H

#include "system-arm.h"
#include "mmu-arm.h"
#include "panic.h"

#include "clock-target.h" /* CPUFREQ_* are defined here */

#ifdef HAVE_SCROLLWHEEL
/* let the timer interrupt twice as often for the scrollwheel polling */
#define KERNEL_TIMER_FREQ (TIMER_FREQ/2)
#else
#define KERNEL_TIMER_FREQ TIMER_FREQ
#endif

#ifdef BOOTLOADER
#define UNCACHED_ADDR(a) (a)
#else
#define UNCACHED_ADDR(a) ((typeof(a)) ((uintptr_t)(a) + 0x10000000))
#endif

#ifdef SANSA_C200V2
/* 0: Backlight on A5, 1: Backlight on A7 */
extern int c200v2_variant;
/* c200v2 changes the timer interval often due to software pwm */
#define TIMER_PERIOD TIMER2_BGLOAD
#else
#define TIMER_PERIOD (KERNEL_TIMER_FREQ/HZ)
#endif

/*
 * This function is not overly accurate, so rather call it with an usec more
 * than less (see below comment)
 * 
 * if inlined it expands to a really small and fast function if it's called
 * with compile time constants */
static inline void udelay(unsigned usecs) __attribute__((always_inline));
static inline void udelay(unsigned usecs)
{
    int now, end;
    
    /**
     * we're limited to 1.5us multiplies due to the odd timer frequency (1.5MHz),
     * to avoid calculating which is safer (need to round up for small values)
     * and saves spending time in the divider we have a lut for
     * small us values, it should be roughly us*2/3
     **/
    static const unsigned char udelay_lut[] =
    {
        0, 1, 2, 2,  3,  4,  4,  5,  6,  6,
        7, 8, 8, 9, 10, 10, 11, 12, 12, 13,
    };


    now = TIMER2_VALUE;
    /* we don't want to handle multiple overflows, so limit the numbers
     * (if you want to wait more than a tick just poll current_tick, or
     * call sleep()) */
    if (UNLIKELY(usecs >= TIMER_PERIOD))
        panicf("%s(): %d too high!", __func__, usecs);
    if (UNLIKELY(usecs <= 0))
        return;
    if (usecs < ARRAYLEN(udelay_lut))
    {   /* the timer decrements */
        end = now - udelay_lut[usecs];
    }
    else
    {   /* to usecs */
        int delay = usecs * 2 / 3; /* us * 1.5 = us*timer_period */
        end = now - delay;
    }
    /* underrun ? */
    if (end < 0)
        end += TIMER_PERIOD;
    while(TIMER2_VALUE != (unsigned)end);
}
#endif /* SYSTEM_TARGET_H */