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, 48 insertions, 16 deletions

diff --git a/src/drivers/ao_cc115l.c b/src/drivers/ao_cc115l.c
index b5103f9b..cf61acfe 100644
--- a/src/drivers/ao_cc115l.c
+++ b/src/drivers/ao_cc115l.c
@@ -249,23 +249,41 @@ ao_radio_idle(void)
 }
 
 /*
- * Packet deviation is 20.5kHz
+ * Packet deviation
  *
  *	fdev = fosc >> 17 * (8 + dev_m) << dev_e
  *
+ * For 38400 baud, use 20.5kHz:
+ *
  *     	26e6 / (2 ** 17) * (8 + 5) * (2 ** 3) = 20630Hz
+ *
+ * For 9600 baud, use 5.125kHz:
+ *
+ *     	26e6 / (2 ** 17) * (8 + 5) * (2 ** 1) = 5157Hz
+ *
+ * For 2400 baud, use 1.5kHz:
+ *
+ *     	26e6 / (2 ** 17) * (8 + 0) * (2 ** 0) = 1587Hz
  */
 
-#define PACKET_DEV_E	3
-#define PACKET_DEV_M	5
+#define PACKET_DEV_E_384	3
+#define PACKET_DEV_M_384	5
+
+#define PACKET_DEV_E_96		1
+#define PACKET_DEV_M_96		5
+
+#define PACKET_DEV_E_24		0
+#define PACKET_DEV_M_24		0
 
 /*
- * For our packet data, set the symbol rate to 38400 Baud
+ * For our packet data:
  *
  *              (256 + DATARATE_M) * 2 ** DATARATE_E
  *	Rdata = -------------------------------------- * fosc
  *		             2 ** 28
  *
+ * For 38400 baud:
+ *
  *		(256 + 131) * (2 ** 10) / (2**28) * 26e6 = 38383
  *
  *	DATARATE_M = 131
@@ -279,20 +297,33 @@ ao_radio_idle(void)
 #define PACKET_DRATE_E_96	8
 #define PACKET_DRATE_E_24	6
 
-static const uint16_t packet_rate_setup[] = {
-	[AO_RADIO_RATE_38400] = ((0xf << 4) |
-				 (PACKET_DRATE_E_384 << CC115L_MDMCFG4_DRATE_E)),
-
-	[AO_RADIO_RATE_9600] = ((0xf << 4) |
-				(PACKET_DRATE_E_96 << CC115L_MDMCFG4_DRATE_E)),
-
-	[AO_RADIO_RATE_2400] = ((0xf << 4) |
-				(PACKET_DRATE_E_24 << CC115L_MDMCFG4_DRATE_E)),
+static const struct {
+	uint8_t		mdmcfg4;
+	uint8_t		deviatn;
+} packet_rate_setup[] = {
+	[AO_RADIO_RATE_38400] = {
+		.mdmcfg4 = ((0xf << 4) |
+			    (PACKET_DRATE_E_384 << CC115L_MDMCFG4_DRATE_E)),
+		.deviatn = ((PACKET_DEV_E_384 << CC115L_DEVIATN_DEVIATION_E) |
+			    (PACKET_DEV_M_384 << CC115L_DEVIATN_DEVIATION_M)),
+	},
+
+	[AO_RADIO_RATE_9600] = {
+		.mdmcfg4 = ((0xf << 4) |
+			    (PACKET_DRATE_E_96 << CC115L_MDMCFG4_DRATE_E)),
+		.deviatn = ((PACKET_DEV_E_96 << CC115L_DEVIATN_DEVIATION_E) |
+			    (PACKET_DEV_M_96 << CC115L_DEVIATN_DEVIATION_M)),
+	},
+
+	[AO_RADIO_RATE_2400] = {
+		.mdmcfg4 = ((0xf << 4) |
+			    (PACKET_DRATE_E_24 << CC115L_MDMCFG4_DRATE_E)),
+		.deviatn = ((PACKET_DEV_E_24 << CC115L_DEVIATN_DEVIATION_E) |
+			    (PACKET_DEV_M_24 << CC115L_DEVIATN_DEVIATION_M)),
+	},
 };
 
 static const uint16_t packet_setup[] = {
-	CC115L_DEVIATN,		((PACKET_DEV_E << CC115L_DEVIATN_DEVIATION_E) |
-				 (PACKET_DEV_M << CC115L_DEVIATN_DEVIATION_M)),
 	CC115L_MDMCFG3,		(PACKET_DRATE_M),
 	CC115L_MDMCFG2,		(0x00 |
 				 (CC115L_MDMCFG2_MOD_FORMAT_GFSK << CC115L_MDMCFG2_MOD_FORMAT) |
@@ -418,7 +449,8 @@ ao_radio_set_mode(uint16_t new_mode)
 
 	changes = new_mode & (~ao_radio_mode);
 	if (changes & AO_RADIO_MODE_BITS_PACKET_TX) {
-		ao_radio_reg_write(CC115L_MDMCFG4, packet_rate_setup[ao_config.radio_rate]);
+		ao_radio_reg_write(CC115L_MDMCFG4, packet_rate_setup[ao_config.radio_rate].mdmcfg4);
+		ao_radio_reg_write(CC115L_DEVIATN, packet_rate_setup[ao_config.radio_rate].deviatn);
 
 		for (i = 0; i < sizeof (packet_setup) / sizeof (packet_setup[0]); i += 2)
 			ao_radio_reg_write(packet_setup[i], packet_setup[i+1]);