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+/*
+ * Asterisk -- An open source telephony toolkit.
+ *
+ * Copyright (C) 1999 - 2005, Digium, Inc.
+ *
+ * Mark Spencer <markster@digium.com>
+ *
+ * See http://www.asterisk.org for more information about
+ * the Asterisk project. Please do not directly contact
+ * any of the maintainers of this project for assistance;
+ * the project provides a web site, mailing lists and IRC
+ * channels for your use.
+ *
+ * This program is free software, distributed under the terms of
+ * the GNU General Public License Version 2. See the LICENSE file
+ * at the top of the source tree.
+ */
+
+/*! \file
+ * \brief TTY/TDD Generation support
+ * \note Includes code and algorithms from the Zapata library.
+ */
+
+#ifndef _ASTERISK_TDD_H
+#define _ASTERISK_TDD_H
+
+#define TDD_BYTES_PER_CHAR 2700
+
+struct tdd_state;
+typedef struct tdd_state TDDSTATE;
+
+/*! CallerID Initialization
+ * Initializes the TDD system. Mostly stuff for inverse FFT
+ */
+void tdd_init(void);
+
+/*! Generates a CallerID FSK stream in ulaw format suitable for transmission.
+ * \param tdd tdd structure
+ * \param buf Buffer to use. This needs to be large enough to accomodate all the generated samples.
+ * \param string This is the string to send.
+ * This function creates a stream of TDD data in ulaw format. It returns the size
+ * (in bytes) of the data (if it returns a size of 0, there is probably an error)
+*/
+int tdd_generate(struct tdd_state *tdd, unsigned char *buf, const char *string);
+
+/*! Create a TDD state machine
+ * This function returns a malloc'd instance of the tdd_state data structure.
+ * Returns a pointer to a malloc'd tdd_state structure, or NULL on error.
+ */
+struct tdd_state *tdd_new(void);
+
+/*! Read samples into the state machine, and return character (if any).
+ * \param tdd Which state machine to act upon
+ * \param ubuf containing your samples
+ * \param samples number of samples contained within the buffer.
+ *
+ * Send received audio to the TDD demodulator.
+ * Returns -1 on error, 0 for "needs more samples",
+ * and > 0 (the character) if reception of a character is complete.
+ */
+int tdd_feed(struct tdd_state *tdd, unsigned char *ubuf, int samples);
+
+/*! Free a TDD state machine
+ * \param tdd This is the tdd_state state machine to free
+ * This function frees tdd_state tdd.
+ */
+void tdd_free(struct tdd_state *tdd);
+
+/*! Generate Echo Canceller disable tone (2100HZ)
+ * \param outbuf This is the buffer to receive the tone data
+ * \param len This is the length (in samples) of the tone data to generate
+ * Returns 0 if no error, and -1 if error.
+ */
+int ast_tdd_gen_ecdisa(unsigned char *outbuf, int len);
+
+
+/*! Generate hold tone
+ * \param outbuf This is the buffer to receive the tone data
+*/
+int tdd_gen_holdtone(unsigned char* outbuf);
+
+#endif /* _ASTERISK_TDD_H */