This also implements more of the FastIO infrastructure.
Unfortunately, definitions aren't exactly straightforward, so we
need lots of tabular data. For example, for the pin function I
I had to step through the user manual, pin by pin.
We also learned a lesson here: Cortex-M0 has a 4 word ( = 16 bytes)
prefetch engine. Loops not starting at such a boundary take
additional 4 clock cycles, making them slower. The tight loop used
for testing previously happened to be 16-byte aligne by accident.
Adding just one line of code in the SET_OUTPUT() macro misaligned
it, so loop repetition rate dropped from 5.3 MHz to 3.7 MHz.
There are many measures to align code to 16-byte boundaries:
- -falign-functions=16 as gcc flag.
- -falign-loops=16 as gcc flag, found to not work.
- -falign-labels=16 as gcc flag, worked for aligning the loop,
but also bloated the binary by 10%.
- __attribute__ ((aligned(16))) attached to functions (not
tested)
- Adding this just before the loop worked fine and increased the
binary by just 16 bytes:
__ASM (".balign 16");
Take care of this when relying on exact execution times, e.g. when
implementing delay_us()!
##############################################################################
# #
# Teacup - lean and efficient firmware for RepRap printers #
# #
# by Triffid Hunter, Traumflug, jakepoz, many others. #
# #
##############################################################################
For installation instructions, see
http://reprap.org/wiki/Teacup_Firmware#Simple_Installation and/or
http://reprap.org/wiki/Teacup_Firmware#Developer_Installation
For documentation, see
http://reprap.org/wiki/Teacup_Firmware
##############################################################################
# #
# This firmware is Copyright (c) ... #
# 2009 - 2010 Michael Moon aka Triffid_Hunter #
# 2010 - 2013 Markus "Traumflug" Hitter <mah@jump-ing.de> #
# #
# 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., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA #
# #
##############################################################################
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