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+/* pwm.avr.c */
+/* asserv - Position & speed motor control on AVR. {{{
+ *
+ * Copyright (C) 2005 Nicolas Schodet
+ *
+ * Robot APB Team/Efrei 2006.
+ * Web: http://assos.efrei.fr/robot/
+ * Email: robot AT efrei DOT fr
+ *
+ * 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.
+ *
+ * }}} */
+
+/** Define the PWM output used for left motor. */
+#define PWM_LEFT_OCR OCR1C
+/** Define the PWM output used for right motor. */
+#define PWM_RIGHT_OCR OCR1B
+/** Define the direction output for left motor. */
+#define PWM_LEFT_DIR 3
+/** Define the direction output for right motor. */
+#define PWM_RIGHT_DIR 2
+
+/** Define the absolute maximum PWM value. */
+#define PWM_MAX 0x3ff
+
+/** PWM values, this is an error if absolute value is greater than the
+ * maximum. */
+int16_t pwm_left, pwm_right;
+/** PWM reverse direction, only set pwm dir bits or you will get weird results
+ * on port B. */
+uint8_t pwm_dir = _BV (PWM_LEFT_DIR);
+
+/* +AutoDec */
+
+/** Initialise PWM generator. */
+static inline void
+pwm_init (void);
+
+/** Update the hardware PWM values. */
+static inline void
+pwm_update (void);
+
+/* -AutoDec */
+
+/** Initialise PWM generator. */
+static inline void
+pwm_init (void)
+{
+ /* Fast PWM, TOP = 0x3ff, OC1B & OC1C with positive logic.
+ f_IO without prescaler.
+ Fpwm = f_IO / (prescaler * (1 + TOP)) = 14400 Hz. */
+ TCCR1A =
+ regv (COM1A1, COM1A0, COM1B1, COM1B0, COM1C1, COM1C0, WGM11, WGM10,
+ 0, 0, 1, 0, 1, 0, 1, 1);
+ TCCR1B = regv (ICNC1, ICES1, 5, WGM13, WGM12, CS12, CS11, CS10,
+ 0, 0, 0, 0, 1, 0, 0, 1);
+ /* Enable pwm and direction outputs in DDRB. */
+ DDRB |= _BV (7) | _BV (6) | _BV (PWM_LEFT_DIR) | _BV (PWM_RIGHT_DIR);
+}
+
+/** Update the hardware PWM values. */
+static inline void
+pwm_update (void)
+{
+ uint16_t left, right;
+ uint8_t dir;
+ /* Some assumption checks. */
+ assert (pwm_left >= -PWM_MAX && pwm_left <= PWM_MAX);
+ assert (pwm_right >= -PWM_MAX && pwm_right <= PWM_MAX);
+ assert ((pwm_dir & ~(_BV (PWM_LEFT_DIR) | _BV (PWM_RIGHT_DIR))) == 0);
+ /* Sample port B. */
+ dir = PORTB & ~(_BV (PWM_LEFT_DIR) | _BV (PWM_RIGHT_DIR));
+ /* Set left PWM. */
+ if (pwm_left == 0)
+ {
+ left = 0;
+ }
+ else if (pwm_left < 0)
+ {
+ left = -pwm_left;
+ }
+ else
+ {
+ dir |= _BV (PWM_LEFT_DIR);
+ left = pwm_left;
+ }
+ /* Set right PWM. */
+ if (pwm_right == 0)
+ {
+ right = 0;
+ }
+ else if (pwm_right < 0)
+ {
+ right = -pwm_right;
+ }
+ else
+ {
+ dir |= _BV (PWM_RIGHT_DIR);
+ right = pwm_right;
+ }
+ /* Setup registers. */
+ /* Here, there could be a problem because OCRx are double buffered, not
+ * PORTB! */
+ /* Another problem arise if the OCR sampling is done between left and
+ * right OCR: the right PWM is one cycle late. */
+ /* A solution could be to use interrupts to update PWM or to synchronise
+ * general timer with PWM. */
+ dir ^= pwm_dir;
+ PORTB = dir;
+ PWM_LEFT_OCR = left;
+ PWM_RIGHT_OCR = right;
+}
+