altos: Reduce deviation at 2400/9600 baud

There's no reason to use 20.5kHz deviation at 2400 and 9600 baud, and
if we get a better receiver, we'll want to use narrower deviation to
have less bandwidth sucking noise into the radio. The new values are
(nominally) 5.125kHz deviation for 9600 baud and 1.5kHz deviation for
2400 baud.

Signed-off-by: Keith Packard <keithp@keithp.com>

1 files changed, 56 insertions, 13 deletions

diff --git a/src/drivers/ao_cc1120.c b/src/drivers/ao_cc1120.c
index 1b907940..3ea8b704 100644
--- a/src/drivers/ao_cc1120.c
+++ b/src/drivers/ao_cc1120.c
@@ -290,15 +290,32 @@ ao_radio_idle(void)
 }
 
 /*
- * Packet deviation is 20.5kHz
+ * Packet deviation
  *
  *	fdev = fosc >> 24 * (256 + dev_m) << dev_e
  *
+ * Deviation for 38400 baud should be 20.5kHz:
+ *
  *     	32e6Hz / (2 ** 24) * (256 + 80) * (2 ** 5) = 20508Hz
+ *
+ * Deviation for 9600 baud should be 5.125kHz:
+ *
+ *     	32e6Hz / (2 ** 24) * (256 + 80) * (2 ** 3) = 5127Hz
+ *
+ * Deviation for 2400 baud should be 1.28125kHz, but cc1111 and
+ * cc115l can't do that, so we'll use 1.5kHz instead:
+ *
+ *     	32e6Hz / (2 ** 24) * (256 + 137) * (2 ** 1) = 1499Hz
  */
 
-#define PACKET_DEV_E	5
-#define PACKET_DEV_M	80
+#define PACKET_DEV_M_384	80
+#define PACKET_DEV_E_384	5
+
+#define PACKET_DEV_M_96		80
+#define PACKET_DEV_E_96		3
+
+#define PACKET_DEV_M_24		137
+#define PACKET_DEV_E_24		1
 
 /*
  * For our packet data
@@ -307,41 +324,55 @@ ao_radio_idle(void)
  *	Rdata = -------------------------------------- * fosc
  *		             2 ** 39
  *
+ * Given the bit period of the baseband, T, the bandwidth of the
+ * baseband signal is B = 1/(2T).  The overall bandwidth of the
+ * modulated signal is then Channel bandwidth = 2Δf + 2B.
+ *
+ * 38400 -- 2 * 20500 + 38400 = 79.4 kHz
+ *  9600 -- 2 * 5.125 +  9600 = 19.9 kHz
+ *  2400 -- 2 * 1.5   +  2400 =  5.4 khz
+ *
  * Symbol rate 38400 Baud:
  *
  *	DATARATE_M = 239914
  *	DATARATE_E = 9
- *	CHANBW = 74.42 (round to 100)
+ *	CHANBW = 79.4 (round to 100)
  *
  * Symbol rate 9600 Baud:
  *
  *	DATARATE_M = 239914
  *	DATARATE_E = 7
- *	CHANBW = 58.58 (round to 62.5)
+ *	CHANBW = 19.9 (round to 20)
  *
  * Symbol rate 2400 Baud:
  *
  *	DATARATE_M = 239914
  *	DATARATE_E = 5
- *	CHANBW = 47.61 (round to 50)
+ *	CHANBW = 5.0 (round to 8.0)
  */
 
 #define PACKET_DRATE_M	239914
 
 #define PACKET_DRATE_E_384	9
-#define PACKET_CHAN_BW_384	0x02	/* 200 / 2 = 100 */
+
+/* 200 / 2 = 100 */
+#define PACKET_CHAN_BW_384	((0 << CC1120_CHAN_BW_CHFILT_BYPASS) | \
+				 (CC1120_CHAN_BW_ADC_CIC_DECFACT_20 << CC1120_CHAN_BW_ADC_CIC_DECFACT) | \
+				 (2 << CC1120_CHAN_BW_BB_CIC_DECFACT))
 
 #define PACKET_DRATE_E_96	7
-#define PACKET_CHAN_BW_96	0x42	/* 125 / 2 = 62.5 */
+/* 200 / 10 = 20 */
+#define PACKET_CHAN_BW_96	((0 << CC1120_CHAN_BW_CHFILT_BYPASS) | \
+				 (CC1120_CHAN_BW_ADC_CIC_DECFACT_20 << CC1120_CHAN_BW_ADC_CIC_DECFACT) | \
+				 (10 << CC1120_CHAN_BW_BB_CIC_DECFACT))
 
 #define PACKET_DRATE_E_24	5
-#define PACKET_CHAN_BW_24	0x04	/* 200 / 4 = 50 */
+/* 200 / 25 = 8 */
+#define PACKET_CHAN_BW_24	((0 << CC1120_CHAN_BW_CHFILT_BYPASS) | \
+				 (CC1120_CHAN_BW_ADC_CIC_DECFACT_20 << CC1120_CHAN_BW_ADC_CIC_DECFACT) | \
+				 (25 << CC1120_CHAN_BW_BB_CIC_DECFACT))
 
 static const uint16_t packet_setup[] = {
-	CC1120_DEVIATION_M,	PACKET_DEV_M,
-	CC1120_MODCFG_DEV_E,	((CC1120_MODCFG_DEV_E_MODEM_MODE_NORMAL << CC1120_MODCFG_DEV_E_MODEM_MODE) |
-				 (CC1120_MODCFG_DEV_E_MOD_FORMAT_2_GFSK << CC1120_MODCFG_DEV_E_MOD_FORMAT) |
-				 (PACKET_DEV_E << CC1120_MODCFG_DEV_E_DEV_E)),
 	CC1120_DRATE1,		((PACKET_DRATE_M >> 8) & 0xff),
 	CC1120_DRATE0,		((PACKET_DRATE_M >> 0) & 0xff),
 	CC1120_PKT_CFG2,	((CC1120_PKT_CFG2_CCA_MODE_ALWAYS_CLEAR << CC1120_PKT_CFG2_CCA_MODE) |
@@ -361,6 +392,10 @@ static const uint16_t packet_setup[] = {
 };
 
 static const uint16_t packet_setup_384[] = {
+	CC1120_DEVIATION_M,	PACKET_DEV_M_384,
+	CC1120_MODCFG_DEV_E,	((CC1120_MODCFG_DEV_E_MODEM_MODE_NORMAL << CC1120_MODCFG_DEV_E_MODEM_MODE) |
+				 (CC1120_MODCFG_DEV_E_MOD_FORMAT_2_GFSK << CC1120_MODCFG_DEV_E_MOD_FORMAT) |
+				 (PACKET_DEV_E_384 << CC1120_MODCFG_DEV_E_DEV_E)),
 	CC1120_DRATE2,		((PACKET_DRATE_E_384 << CC1120_DRATE2_DATARATE_E) |
 				 (((PACKET_DRATE_M >> 16) & CC1120_DRATE2_DATARATE_M_19_16_MASK) << CC1120_DRATE2_DATARATE_M_19_16)),
 	CC1120_CHAN_BW,		PACKET_CHAN_BW_384,
@@ -368,6 +403,10 @@ static const uint16_t packet_setup_384[] = {
 };
 
 static const uint16_t packet_setup_96[] = {
+	CC1120_DEVIATION_M,	PACKET_DEV_M_96,
+	CC1120_MODCFG_DEV_E,	((CC1120_MODCFG_DEV_E_MODEM_MODE_NORMAL << CC1120_MODCFG_DEV_E_MODEM_MODE) |
+				 (CC1120_MODCFG_DEV_E_MOD_FORMAT_2_GFSK << CC1120_MODCFG_DEV_E_MOD_FORMAT) |
+				 (PACKET_DEV_E_96 << CC1120_MODCFG_DEV_E_DEV_E)),
 	CC1120_DRATE2,		((PACKET_DRATE_E_96 << CC1120_DRATE2_DATARATE_E) |
 				 (((PACKET_DRATE_M >> 16) & CC1120_DRATE2_DATARATE_M_19_16_MASK) << CC1120_DRATE2_DATARATE_M_19_16)),
 	CC1120_CHAN_BW,		PACKET_CHAN_BW_96,
@@ -375,6 +414,10 @@ static const uint16_t packet_setup_96[] = {
 };
 
 static const uint16_t packet_setup_24[] = {
+	CC1120_DEVIATION_M,	PACKET_DEV_M_24,
+	CC1120_MODCFG_DEV_E,	((CC1120_MODCFG_DEV_E_MODEM_MODE_NORMAL << CC1120_MODCFG_DEV_E_MODEM_MODE) |
+				 (CC1120_MODCFG_DEV_E_MOD_FORMAT_2_GFSK << CC1120_MODCFG_DEV_E_MOD_FORMAT) |
+				 (PACKET_DEV_E_24 << CC1120_MODCFG_DEV_E_DEV_E)),
 	CC1120_DRATE2,		((PACKET_DRATE_E_24 << CC1120_DRATE2_DATARATE_E) |
 				 (((PACKET_DRATE_M >> 16) & CC1120_DRATE2_DATARATE_M_19_16_MASK) << CC1120_DRATE2_DATARATE_M_19_16)),
 	CC1120_CHAN_BW,		PACKET_CHAN_BW_24,