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/* RF Channel utilities */
/* (C) 2010 by Sylvain Munaut <tnt@246tNt.com>
*
* All Rights Reserved
*
* 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 Street, Fifth Floor, Boston, MA 02110-1301 USA.
*
*/
#include <stdint.h>
#include <osmocom/gsm/gsm_utils.h>
#include <layer1/sync.h>
/*
* Hopping sequence generation
*
* The algorithm is explained in GSM 05.02 Section 6.2.3
*
* if HSN = 0 (cyclic hopping) then:
* MAI, integer (0 .. N-1) :
* MAI = (FN + MAIO) modulo N
*
* else:
* M, integer (0 .. 152) :
* M = T2 + RNTABLE((HSN xor T1R) + T3)
*
* S, integer (0 .. N-1) :
* M' = M modulo (2 ^ NBIN)
* T' = T3 modulo (2 ^ NBIN)
*
* if M' < N then:
* S = M'
* else:
* S = (M'+T') modulo N
*
* MAI, integer (0 .. N-1) :
* MAI = (S + MAIO) modulo N
*/
static uint8_t rn_table[114] = {
48, 98, 63, 1, 36, 95, 78, 102, 94, 73,
0, 64, 25, 81, 76, 59, 124, 23, 104, 100,
101, 47, 118, 85, 18, 56, 96, 86, 54, 2,
80, 34, 127, 13, 6, 89, 57, 103, 12, 74,
55, 111, 75, 38, 109, 71, 112, 29, 11, 88,
87, 19, 3, 68, 110, 26, 33, 31, 8, 45,
82, 58, 40, 107, 32, 5, 106, 92, 62, 67,
77, 108, 122, 37, 60, 66, 121, 42, 51, 126,
117, 114, 4, 90, 43, 52, 53, 113, 120, 72,
16, 49, 7, 79, 119, 61, 22, 84, 9, 97,
91, 15, 21, 24, 46, 39, 93, 105, 65, 70,
125, 99, 17, 123,
};
static int pow_nbin_mask(int n)
{
int x;
x = (n ) |
(n >> 1) |
(n >> 2) |
(n >> 3) |
(n >> 4) |
(n >> 5) |
(n >> 6);
return x;
}
/*! Hopping sequence generator.
* \param[in] t GSM time (frame number)
* \param[in] hsn Hopping Sequence Number
* \param[in] maio Mobile Allocation Index OFfset
* \param[in] n number of entries in mobile allocation (arfcn table)
* \param[in] arfcn_tbl Array of ARFCN representing the mobile allocation
* \returns ARFCN to use for given input parameters at time 't' or MAI if arfcn_tbl == NULL */
static int16_t rfch_hop_seq_gen(const struct gsm_time *t,
uint8_t hsn, uint8_t maio,
uint8_t n, const uint16_t *arfcn_tbl)
{
int mai;
if (!hsn) {
/* cyclic hopping */
mai = (t->fn + maio) % n;
} else {
/* pseudo random hopping */
int m, mp, tp, s, pnm;
pnm = pow_nbin_mask(n);
m = t->t2 + rn_table[(hsn ^ (t->t1 & 63)) + t->t3];
mp = m & pnm;
if (mp < n)
s = mp;
else {
tp = t->t3 & pnm;
s = (mp + tp) % n;
}
mai = (s + maio) % n;
}
return arfcn_tbl ? arfcn_tbl[mai] : mai;
}
/*! Get RF Channel parameters at a given GSM time (frame number)
* \param[in] t GSM time for which to obtain parameters
* \param[out] arfcn_p ARFCN to use at time t
* \oaram[out] tsc_p Training sequence to use at time t
* \param[out] tn_p Timeslot Number to use at time t */
void rfch_get_params(const struct gsm_time *t,
uint16_t *arfcn_p, uint8_t *tsc_p, uint8_t *tn_p)
{
if (l1s.dedicated.type == GSM_DCHAN_NONE) {
/* Serving cell only */
if (arfcn_p)
*arfcn_p = l1s.serving_cell.arfcn;
if (tsc_p)
*tsc_p = l1s.serving_cell.bsic & 0x7;
if (tn_p)
*tn_p = 0;
} else {
/* Dedicated channel */
if (arfcn_p) {
if (l1s.dedicated.h) {
*arfcn_p = rfch_hop_seq_gen(t,
l1s.dedicated.h1.hsn,
l1s.dedicated.h1.maio,
l1s.dedicated.h1.n,
l1s.dedicated.h1.ma);
} else {
*arfcn_p = l1s.dedicated.h0.arfcn;
}
}
if (tsc_p)
*tsc_p = l1s.dedicated.tsc;
if (tn_p)
*tn_p = l1s.dedicated.tn;
}
}
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