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diff --git a/digital/ucoolib/ucoolib/utils/delay.arm.cc b/digital/ucoolib/ucoolib/utils/delay.arm.cc
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+// ucoolib - Microcontroller object oriented library. {{{
+//
+// Copyright (C) 2012 Nicolas Schodet
+//
+// APBTeam:
+// Web: http://apbteam.org/
+// Email: team AT apbteam DOT org
+//
+// 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 program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program; if not, write to the Free Software
+// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+//
+// }}}
+#include "delay.arm.hh"
+
+#include <algorithm>
+
+#include <libopencm3/stm32/systick.h>
+#include <libopencm3/stm32/f4/rcc.h>
+
+namespace ucoo {
+
+void
+delay_us (int us)
+{
+ // Horrible hack: there is no record of the current systick speed, make
+ // guesses based on APB2 clock. Also, suppose that frequency is a multiple
+ // of 1 MHz (to avoid 64 bit division).
+ int systick_mhz = rcc_ppre2_frequency / (4 * 1000000);
+ int cycles = systick_mhz * us;
+ STK_CTRL = 0;
+ // Loop several times if cycles is too big for the systick timer. Some
+ // nanoseconds are lost every second, I can live with that, it simplifies
+ // code.
+ while (cycles)
+ {
+ int loop_cycles = std::min (1 << 24, cycles);
+ STK_LOAD = loop_cycles - 1;
+ STK_VAL = 0;
+ STK_CTRL = STK_CTRL_ENABLE;
+ while (!(STK_CTRL & STK_CTRL_COUNTFLAG))
+ ;
+ STK_CTRL = 0;
+ cycles -= loop_cycles;
+ }
+}
+
+void
+delay_ns (int ns)
+{
+ // Horrible hack: there is no record of the current hclock speed, make
+ // guesses based on APB2 clock. Also, suppose that frequency is a multiple
+ // of 1 MHz (to avoid 64 bit division).
+ int hclock_mhz = rcc_ppre2_frequency / (1000000 / 2);
+ int cycles = (hclock_mhz * ns + 999) / 1000;
+ STK_CTRL = 0;
+ // Loop once, ns is supposed to be small.
+ STK_LOAD = cycles - 1;
+ STK_VAL = 0;
+ STK_CTRL = STK_CTRL_CLKSOURCE_AHB | STK_CTRL_ENABLE;
+ while (!(STK_CTRL & STK_CTRL_COUNTFLAG))
+ ;
+ STK_CTRL = 0;
+}
+
+} // namespace ucoo