gsm: Add method to find ARFCN based on frequency
Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
diff --git a/include/osmocom/gsm/gsm_utils.h b/include/osmocom/gsm/gsm_utils.h
index 6d31672..1767898 100644
--- a/include/osmocom/gsm/gsm_utils.h
+++ b/include/osmocom/gsm/gsm_utils.h
@@ -101,6 +101,9 @@
/* Convert an ARFCN to the frequency in MHz * 10 */
uint16_t gsm_arfcn2freq10(uint16_t arfcn, int uplink);
+/* Convert a Frequency in MHz * 10 to ARFCN */
+uint16_t gsm_freq102arfcn(uint16_t freq10, int uplink);
+
/* Convert from frame number to GSM time */
void gsm_fn2gsmtime(struct gsm_time *time, uint32_t fn);
diff --git a/src/gsm/gsm_utils.c b/src/gsm/gsm_utils.c
index 8b1fae0..ecebde8 100644
--- a/src/gsm/gsm_utils.c
+++ b/src/gsm/gsm_utils.c
@@ -503,59 +503,79 @@
return GSM_BAND_1800;
}
+struct gsm_freq_range {
+ uint16_t arfcn_first;
+ uint16_t arfcn_last;
+ uint16_t freq_ul_first;
+ uint16_t freq_dl_offset;
+ uint16_t flags;
+};
+
+static struct gsm_freq_range gsm_ranges[] = {
+ { 512, 810, 18502, 800, ARFCN_PCS }, /* PCS 1900 */
+ { 0, 124, 8900, 450, 0 }, /* P-GSM + E-GSM ARFCN 0 */
+ { 955, 1023, 8762, 450, 0 }, /* E-GSM + R-GSM */
+ { 128, 251, 8242, 450, 0 }, /* GSM 850 */
+ { 512, 885, 17102, 950, 0 }, /* DCS 1800 */
+ { 259, 293, 4506, 100, 0 }, /* GSM 450 */
+ { 306, 340, 4790, 100, 0 }, /* GSM 480 */
+ { 350, 425, 8060, 450, 0 }, /* GSM 810 */
+ { 438, 511, 7472, 300, 0 }, /* GSM 750 */
+ { /* Guard */ }
+};
+
/* Convert an ARFCN to the frequency in MHz * 10 */
uint16_t gsm_arfcn2freq10(uint16_t arfcn, int uplink)
{
- uint16_t freq10_ul;
- uint16_t freq10_dl;
- int is_pcs = arfcn & ARFCN_PCS;
+ struct gsm_freq_range *r;
+ uint16_t flags = arfcn & ARFCN_FLAG_MASK;
+ uint16_t freq10_ul = 0xffff;
+ uint16_t freq10_dl = 0xffff;
arfcn &= ~ARFCN_FLAG_MASK;
- if (is_pcs) {
- /* DCS 1900 */
- arfcn &= ~ARFCN_PCS;
- freq10_ul = 18502 + 2 * (arfcn-512);
- freq10_dl = freq10_ul + 800;
- } else if (arfcn <= 124) {
- /* Primary GSM + ARFCN 0 of E-GSM */
- freq10_ul = 8900 + 2 * arfcn;
- freq10_dl = freq10_ul + 450;
- } else if (arfcn >= 955 && arfcn <= 1023) {
- /* E-GSM and R-GSM */
- freq10_ul = 8900 + 2 * (arfcn - 1024);
- freq10_dl = freq10_ul + 450;
- } else if (arfcn >= 128 && arfcn <= 251) {
- /* GSM 850 */
- freq10_ul = 8242 + 2 * (arfcn - 128);
- freq10_dl = freq10_ul + 450;
- } else if (arfcn >= 512 && arfcn <= 885) {
- /* DCS 1800 */
- freq10_ul = 17102 + 2 * (arfcn - 512);
- freq10_dl = freq10_ul + 950;
- } else if (arfcn >= 259 && arfcn <= 293) {
- /* GSM 450 */
- freq10_ul = 4506 + 2 * (arfcn - 259);
- freq10_dl = freq10_ul + 100;
- } else if (arfcn >= 306 && arfcn <= 340) {
- /* GSM 480 */
- freq10_ul = 4790 + 2 * (arfcn - 306);
- freq10_dl = freq10_ul + 100;
- } else if (arfcn >= 350 && arfcn <= 425) {
- /* GSM 810 */
- freq10_ul = 8060 + 2 * (arfcn - 350);
- freq10_dl = freq10_ul + 450;
- } else if (arfcn >= 438 && arfcn <= 511) {
- /* GSM 750 */
- freq10_ul = 7472 + 2 * (arfcn - 438);
- freq10_dl = freq10_ul + 300;
- } else
- return 0xffff;
+ for (r=gsm_ranges; r->freq_ul_first>0; r++) {
+ if ((flags == r->flags) &&
+ (arfcn >= r->arfcn_first) &&
+ (arfcn <= r->arfcn_last))
+ {
+ freq10_ul = r->freq_ul_first + 2 * (arfcn - r->arfcn_first);
+ freq10_dl = freq10_ul + r->freq_dl_offset;
+ break;
+ }
+ }
+
+ return uplink ? freq10_ul : freq10_dl;
+}
+
+/* Convert a Frequency in MHz * 10 to ARFCN */
+uint16_t gsm_freq102arfcn(uint16_t freq10, int uplink)
+{
+ struct gsm_freq_range *r;
+ uint16_t freq10_lo, freq10_hi;
+ uint16_t arfcn = 0xffff;
+
+ for (r=gsm_ranges; r->freq_ul_first>0; r++) {
+ /* Generate frequency limits */
+ freq10_lo = r->freq_ul_first;
+ freq10_hi = freq10_lo + 2 * (r->arfcn_last - r->arfcn_first);
+ if (!uplink) {
+ freq10_lo += r->freq_dl_offset;
+ freq10_hi += r->freq_dl_offset;
+ }
+
+ /* Check if this fits */
+ if (freq10 >= freq10_lo && freq10 <= freq10_hi) {
+ arfcn = r->arfcn_first + ((freq10 - freq10_lo) >> 1);
+ arfcn |= r->flags;
+ break;
+ }
+ }
if (uplink)
- return freq10_ul;
- else
- return freq10_dl;
+ arfcn |= ARFCN_UPLINK;
+
+ return arfcn;
}
void gsm_fn2gsmtime(struct gsm_time *time, uint32_t fn)
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index 3373888..b2278f1 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -137,6 +137,7 @@
gsm_arfcn2band;
gsm_arfcn2freq10;
+gsm_freq102arfcn;
gsm_band_name;
gsm_band_parse;
gsm_fn2gsmtime;