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libosmo-netif/src/amr.c

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/*
* (C) 2012 by Pablo Neira Ayuso <pablo@gnumonks.org>
* (C) 2012 by On Waves ehf <http://www.on-waves.com>
*
* SPDX-License-Identifier: GPL-2.0+
*
* 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.
*/
#include <stdint.h>
#include <unistd.h>
#include <string.h>
#include <stdbool.h>
#include <osmocom/core/utils.h>
#include <osmocom/netif/amr.h>
/* According to TS 26.101 Table A.1b:
*
* Frame type AMR code bits bytes
* 0 4.75 95 12
* 1 5.15 103 13
* 2 5.90 118 15
* 3 6.70 134 17
* 4 7.40 148 19
* 5 7.95 159 20
* 6 10.20 204 26
* 7 12.20 244 31
* 8 AMR SID 39 5
* 9 GSM-EFR SID 43 5
* 10 TDMA-EFR SID 38 5
* 11 PDC-EFR SID 37 5
* 12 NOT USED
* 13 NOT USED
* 14 NOT USED
* 15 NO DATA 0 0
*/
static int amr_ft_to_bits[AMR_FT_MAX] = {
[AMR_FT_0] = AMR_FT_0_LEN_BITS,
[AMR_FT_1] = AMR_FT_1_LEN_BITS,
[AMR_FT_2] = AMR_FT_2_LEN_BITS,
[AMR_FT_3] = AMR_FT_3_LEN_BITS,
[AMR_FT_4] = AMR_FT_4_LEN_BITS,
[AMR_FT_5] = AMR_FT_5_LEN_BITS,
[AMR_FT_6] = AMR_FT_6_LEN_BITS,
[AMR_FT_7] = AMR_FT_7_LEN_BITS,
[AMR_FT_SID] = AMR_FT_SID_LEN_BITS,
[AMR_FT_GSM_EFR_SID] = AMR_FT_GSM_EFR_SID_LEN_BITS,
[AMR_FT_TDMA_EFR_SID] = AMR_FT_TDMA_EFR_SID_LEN_BITS,
[AMR_FT_PDC_EFR_SID] = AMR_FT_PDC_EFR_SID_LEN_BITS,
[12] = 0, /* for future use */
[13] = 0, /* for future use */
[14] = 0, /* for future use */
[AMR_FT_NO_DATA] = AMR_FT_NO_DATA_LEN_BITS,
};
static size_t amr_ft_to_bytes[AMR_FT_MAX] = {
[AMR_FT_0] = AMR_FT_0_LEN,
[AMR_FT_1] = AMR_FT_1_LEN,
[AMR_FT_2] = AMR_FT_2_LEN,
[AMR_FT_3] = AMR_FT_3_LEN,
[AMR_FT_4] = AMR_FT_4_LEN,
[AMR_FT_5] = AMR_FT_5_LEN,
[AMR_FT_6] = AMR_FT_6_LEN,
[AMR_FT_7] = AMR_FT_7_LEN,
[AMR_FT_SID] = AMR_FT_SID_LEN,
[AMR_FT_GSM_EFR_SID] = AMR_FT_GSM_EFR_SID_LEN,
[AMR_FT_TDMA_EFR_SID] = AMR_FT_TDMA_EFR_SID_LEN,
[AMR_FT_PDC_EFR_SID] = AMR_FT_PDC_EFR_SID_LEN,
[12] = 0, /* for future use */
[13] = 0, /* for future use */
[14] = 0, /* for future use */
[AMR_FT_NO_DATA] = AMR_FT_NO_DATA_LEN,
};
size_t osmo_amr_bits(uint8_t amr_ft)
{
OSMO_ASSERT(amr_ft < AMR_FT_MAX);
return amr_ft_to_bits[amr_ft];
}
size_t osmo_amr_bytes(uint8_t amr_ft)
{
OSMO_ASSERT(amr_ft < AMR_FT_MAX);
return amr_ft_to_bytes[amr_ft];
}
int osmo_amr_bytes_to_ft(size_t bytes)
{
int ft;
for (ft = 0; ft < AMR_FT_PDC_EFR_SID; ft++) {
if (amr_ft_to_bytes[ft] == bytes)
return ft;
}
/* 12-14 not used, jump to 15 (AMR_FT_NO_DATA): */
if (amr_ft_to_bytes[AMR_FT_NO_DATA] == bytes)
return AMR_FT_NO_DATA;
return -1;
}
int osmo_amr_ft_valid(uint8_t amr_ft)
{
return amr_ft <= AMR_FT_PDC_EFR_SID || amr_ft == AMR_FT_NO_DATA;
}
/*! Check if an AMR frame is octet aligned by looking at the padding bits.
* \param[inout] payload user provided memory containing the AMR payload.
* \param[in] payload_len overall length of the AMR payload.
* \returns true when the payload is octet aligned. */
bool osmo_amr_is_oa(const uint8_t *payload, unsigned int payload_len)
{
/* NOTE: The distinction between octet-aligned and bandwith-efficient
* mode normally relys on out of band methods that explicitly select
* one of the two modes. (See also RFC 3267, chapter 3.8). However the
* A interface in GSM does not provide ways to communicate which mode
* is exactly used. The following functions uses some heuristics to
* check if an AMR payload is octet aligned or not. */
struct amr_hdr *oa_hdr = (struct amr_hdr *)payload;
unsigned int frame_len;
/* Broken payload? */
if (!payload || payload_len < sizeof(struct amr_hdr))
return false;
/* In octet aligned mode, padding bits are specified to be
* set to zero. (However, there is a remaining risk that the FT0 or FT1
* is selected and the first two bits of the frame are zero as well,
* in this case a bandwith-efficient mode payload would look like an
* octet-aligned payload, thats why additional checks are required.) */
if (oa_hdr->pad1 != 0)
return false;
if (oa_hdr->pad2 != 0)
return false;
/* This implementation is limited to single-frame payloads only and
* since multi-frame payloads are not common in GSM anyway, we may
* include the final bit of the first header into this check. */
if (oa_hdr->f != 0)
return false;
/* Match the length of the received payload against the expected frame
* length that is defined by the frame type. */
if (!osmo_amr_ft_valid(oa_hdr->ft))
return false;
frame_len = osmo_amr_bytes(oa_hdr->ft);
if (frame_len != payload_len - sizeof(struct amr_hdr))
return false;
return true;
}
/*! Convert an AMR frame from octet-aligned mode to bandwith-efficient mode.
* \param[inout] payload user provided memory containing the AMR payload.
* \param[in] payload_len overall length of the AMR payload.
* \returns resulting payload length, -1 on error. */
int osmo_amr_oa_to_bwe(uint8_t *payload, unsigned int payload_len)
{
struct amr_hdr *oa_hdr = (struct amr_hdr *)payload;
unsigned int ft = oa_hdr->ft;
unsigned int frame_len = payload_len - sizeof(struct amr_hdr);
unsigned int i;
int bwe_payload_len;
/* This implementation is not capable to handle multi-frame
* packets, so we need to make sure that the frame we operate on
* contains only one payload. */
if (oa_hdr->f != 0)
return -1;
/* Check for valid FT (AMR mode) value */
if (!osmo_amr_ft_valid(oa_hdr->ft))
return -1;
/* Move TOC close to CMR */
payload[0] = (payload[0] & 0xf0) | ((payload[1] >> 4) & 0x0f);
payload[1] = (payload[1] << 4) & 0xf0;
for (i = 0; i < frame_len; i++) {
payload[i + 1] |= payload[i + 2] >> 2;
payload[i + 2] = payload[i + 2] << 6;
}
/* Calculate new payload length */
bwe_payload_len = OSMO_BYTES_FOR_BITS(AMR_HDR_BWE_LEN_BITS + osmo_amr_bits(ft));
return bwe_payload_len;
}
/*! Convert an AMR frame from bandwith-efficient mode to octet-aligned mode.
* \param[inout] payload user provided memory containing the AMR payload.
* \param[in] payload_len overall length of the AMR payload.
* \param[in] payload_maxlen maximum length of the user provided memory.
* \returns resulting payload length, -1 on error. */
int osmo_amr_bwe_to_oa(uint8_t *payload, unsigned int payload_len,
unsigned int payload_maxlen)
{
uint8_t buf[256];
/* The header is only valid after shifting first two bytes to OA mode */
struct amr_hdr_bwe *bwe_hdr = (struct amr_hdr_bwe *)payload;
struct amr_hdr *oa_hdr;
unsigned int i;
unsigned int oa_payload_len;
uint8_t ft;
if (payload_len < sizeof(struct amr_hdr_bwe))
return -1;
if (payload_len + 1 > payload_maxlen)
return -1;
if (payload_len + 1 > sizeof(buf))
return -1;
ft = (bwe_hdr->ft_hi << 1) | bwe_hdr->ft_lo;
if (!osmo_amr_ft_valid(ft))
return -1;
if (OSMO_BYTES_FOR_BITS(AMR_HDR_BWE_LEN_BITS + osmo_amr_bits(ft)) > payload_len)
return -1;
memset(buf, 0, sizeof(buf));
oa_hdr = (struct amr_hdr *)buf;
oa_hdr->cmr = bwe_hdr->cmr;
oa_hdr->f = bwe_hdr->f;
oa_hdr->ft = ft;
oa_hdr->q = bwe_hdr->q;
/* Calculate new payload length */
oa_payload_len = 2 + osmo_amr_bytes(ft);
for (i = 2; i < oa_payload_len - 1; i++) {
buf[i] = payload[i - 1] << 2;
buf[i] |= payload[i] >> 6;
}
buf[i] = payload[i - 1] << 2;
memcpy(payload, buf, oa_payload_len);
return oa_payload_len;
}
/*! Convert an AMR frame from bandwith-efficient mode to IuuP/IuFP payload.
* The IuuP/IuPF payload only contains the class a, b, c bits. No header.
* \param[inout] payload user provided memory containing the AMR payload.
* \param[in] payload_len overall length of the AMR payload.
* \param[in] payload_maxlen maximum length of the user provided memory.
* \returns resulting payload length, negative on error. */
int osmo_amr_bwe_to_iuup(uint8_t *payload, unsigned int payload_len)
{
/* The header is only valid after shifting first two bytes to OA mode */
unsigned int i, required_len_bits;
unsigned int amr_speech_len_bytes, amr_speech_len_bits;
uint8_t ft;
if (payload_len < 2)
return -1;
/* Calculate new payload length */
ft = ((payload[0] & 0x07) << 1) | ((payload[1] & 0x80) >> 7);
if (!osmo_amr_ft_valid(ft))
return -1;
amr_speech_len_bits = osmo_amr_bits(ft);
amr_speech_len_bytes = osmo_amr_bytes(ft);
/* shift of AMR_HDR_BWE_LEN_BITS (10) bits, aka remove BWE Hdr + ToC: */
required_len_bits = AMR_HDR_BWE_LEN_BITS + amr_speech_len_bits;
if (payload_len < OSMO_BYTES_FOR_BITS(required_len_bits))
return -1;
for (i = 0; i < amr_speech_len_bytes; i++) {
/* we have to shift the payload by 10 bits to get only the Class A, B, C bits */
payload[i] = (payload[i + 1] << 2) | ((payload[i + 2]) >> 6);
}
return amr_speech_len_bytes;
}
/*! Convert an AMR frame from IuuP/IuFP payload to bandwith-efficient mode.
* The IuuP/IuPF payload only contains the class a, b, c bits. No header.
* The resulting buffer has space at the start prepared to be filled by CMR, TOC.
* \param[inout] payload user provided memory containing the AMR payload.
* \param[in] payload_len overall length of the AMR payload.
* \param[in] payload_maxlen maximum length of the user provided memory (payload_len + 2 required).
* \returns resulting payload length, negative on error. */
int osmo_amr_iuup_to_bwe(uint8_t *payload, unsigned int payload_len,
unsigned int payload_maxlen)
{
/* shift all bits by AMR_HDR_BWE_LEN_BITS (10) */
unsigned int i, required_len_bits, required_len_bytes;
int ft = osmo_amr_bytes_to_ft(payload_len);
if (ft < 0)
return ft;
required_len_bits = osmo_amr_bits(ft) + 10;
required_len_bytes = OSMO_BYTES_FOR_BITS(required_len_bits);
if (payload_maxlen < required_len_bytes)
return -1;
i = payload_len + 1;
payload[i] = (payload[i - 2] << 6);
for (i = payload_len; i >= 2; i--) {
/* we have to shift the payload by AMR_HDR_BWE_LEN_BITS (10) bits to prepend BWE Hdr + ToC */
payload[i] = (payload[i - 1] >> 2) | (payload[i - 2] << 6);
}
payload[i] = (payload[i - 1] >> 2);
payload[0] = 0;
return required_len_bytes;
}
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