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diff --git a/digital/avr/modules/twi/twi_soft.avr.c b/digital/avr/modules/twi/twi_soft.avr.c
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+/* twi_soft.avr.c - Software master implementation. */
+/* avr.twi - TWI AVR module. {{{
+ *
+ * Copyright (C) 2010 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 "common.h"
+#include "twi.h"
+
+#if TWI_DRIVER == TWI_DRIVER_SOFT
+
+# include "modules/utils/utils.h"
+# include "io.h"
+
+# if AC_TWI_SLAVE_ENABLE
+# error "twi: slave mode not supported by software driver"
+# endif
+# if AC_TWI_NO_INTERRUPT
+# warning "twi: no interrupt anyway"
+# endif
+
+/* Define IO shortcuts. */
+# define SDA_IO AC_TWI_SOFT_SDA_IO
+# define SCL_IO AC_TWI_SOFT_SCL_IO
+
+# if AC_TWI_PULL_UP
+# define SDA_0 do { IO_CLR (SDA_IO); IO_OUTPUT (SDA_IO); } while (0)
+# define SDA_1 do { IO_INPUT (SDA_IO); IO_SET (SDA_IO); } while (0)
+# define SCL_0 do { IO_CLR (SCL_IO); IO_OUTPUT (SCL_IO); } while (0)
+# define SCL_1 do { IO_INPUT (SCL_IO); IO_SET (SCL_IO); } while (0)
+# else
+# define SDA_0 do { IO_OUTPUT (SDA_IO); } while (0)
+# define SDA_1 do { IO_INPUT (SDA_IO); } while (0)
+# define SCL_0 do { IO_OUTPUT (SCL_IO); } while (0)
+# define SCL_1 do { IO_INPUT (SCL_IO); } while (0)
+# endif
+
+# if AC_TWI_MASTER_ENABLE
+
+/** Current master status. */
+uint8_t twi_master_current_status;
+
+# endif
+
+void
+twi_init (uint8_t addr)
+{
+#if AC_TWI_PULL_UP
+ SDA_1;
+ SCL_1;
+#else
+ IO_CLR (SDA_IO);
+ SDA_1;
+ IO_CLR (SCL_IO);
+ SCL_1;
+#endif
+}
+
+void
+twi_uninit (void)
+{
+ /* Keep pull-up. */
+}
+
+# if AC_TWI_MASTER_ENABLE
+
+/** Wait a half bit period. */
+static void
+twi_delay (void)
+{
+ utils_delay (0.5 / AC_TWI_FREQ);
+}
+
+/** Wait until SCL is high to enable clock stretching. */
+static inline void
+twi_wait_scl (void)
+{
+ while (!IO_GET (SCL_IO))
+ ;
+}
+
+/** Send start condition. */
+static void
+twi_master_send_start (void)
+{
+ SDA_0;
+ twi_delay ();
+ SCL_0;
+ twi_delay ();
+}
+
+/** Send stop condition. */
+static void
+twi_master_send_stop (void)
+{
+ SDA_0;
+ twi_delay ();
+ SCL_1;
+ twi_wait_scl ();
+ twi_delay ();
+ SDA_1;
+ twi_delay ();
+}
+
+/** Send one bit. */
+static void
+twi_master_send_bit (uint8_t bit)
+{
+ if (bit)
+ SDA_1;
+ else
+ SDA_0;
+ twi_delay ();
+ SCL_1;
+ twi_wait_scl ();
+ twi_delay ();
+ SCL_0;
+}
+
+/** Receive one bit. */
+static uint8_t
+twi_master_recv_bit (void)
+{
+ SDA_1;
+ twi_delay ();
+ SCL_1;
+ twi_wait_scl ();
+ uint8_t bit = IO_GET (SDA_IO) ? 1 : 0;
+ twi_delay ();
+ SCL_0;
+ return bit;
+}
+
+/** Send one byte, return the received nack bit. */
+static uint8_t
+twi_master_send_byte (uint8_t b)
+{
+ uint8_t i;
+ for (i = 8; i; i--)
+ {
+ twi_master_send_bit (b & 0x80);
+ b <<= 1;
+ }
+ return twi_master_recv_bit ();
+}
+
+/** Receive one byte, send the nack bit. */
+static uint8_t
+twi_master_recv_byte (uint8_t nack)
+{
+ uint8_t i, b;
+ b = 0;
+ for (i = 8; i; i--)
+ {
+ b <<= 1;
+ b |= twi_master_recv_bit ();
+ }
+ twi_master_send_bit (nack);
+ return b;
+}
+
+void
+twi_master_send (uint8_t addr, const uint8_t *buffer, uint8_t size)
+{
+ uint8_t nack, sent = 0;
+ /* Start. */
+ twi_master_send_start ();
+ /* Send SLA+W. */
+ nack = twi_master_send_byte (addr | 0);
+ /* Send data. */
+ for (; !nack && sent < size; sent++)
+ nack = twi_master_send_byte (buffer[sent]);
+ /* Stop. */
+ twi_master_send_stop ();
+ /* Update status, there is no background task. */
+ twi_master_current_status = sent;
+ /* If defined, call master done callback. */
+#ifdef AC_TWI_MASTER_DONE
+ AC_TWI_MASTER_DONE ();
+#endif
+}
+
+void
+twi_master_recv (uint8_t addr, uint8_t *buffer, uint8_t size)
+{
+ uint8_t nack, recv = 0;
+ /* Start. */
+ twi_master_send_start ();
+ /* Send SLA+R. */
+ nack = twi_master_send_byte (addr | 1);
+ if (!nack)
+ {
+ /* Receive data, send nack in last byte. */
+ for (; recv < size; recv++)
+ buffer[recv] = twi_master_recv_byte (recv == size - 1 ? 1 : 0);
+ }
+ /* Stop. */
+ twi_master_send_stop ();
+ /* Update status, there is no background task. */
+ twi_master_current_status = recv;
+ /* If defined, call master done callback. */
+#ifdef AC_TWI_MASTER_DONE
+ AC_TWI_MASTER_DONE ();
+#endif
+}
+
+uint8_t
+twi_master_status (void)
+{
+ return twi_master_current_status;
+}
+
+uint8_t
+twi_master_wait (void)
+{
+ /* No background task, nothing to wait. */
+ return twi_master_current_status;
+}
+
+# endif /* AC_TWI_MASTER_ENABLE */
+
+#endif /* TWI_DRIVER == TWI_DRIVER_SOFT */