From a7f9cb93be4fdf5ef39de0c8860d5da05529da8a Mon Sep 17 00:00:00 2001
From: Bryan Biedenkapp <gatekeep@gmail.com>
Date: Mon, 3 Jun 2024 11:36:22 -0400
Subject: [PATCH] fix issue handling $F7E NAC; implement $F7F NAC support;

---
 src/common/p25/NID.cpp      | 14 +++++++++++++-
 src/common/p25/NID.h        |  2 +-
 src/common/p25/P25Defines.h |  4 ++++
 src/common/p25/P25Utils.h   |  4 ++--
 src/host/Host.Config.cpp    | 11 +++++++----
 5 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/src/common/p25/NID.cpp b/src/common/p25/NID.cpp
index 4090c57f..82a7c65b 100644
--- a/src/common/p25/NID.cpp
+++ b/src/common/p25/NID.cpp
@@ -13,6 +13,7 @@
 *
 */
 #include "Defines.h"
+#include "common/Utils.h"
 #include "p25/P25Defines.h"
 #include "p25/NID.h"
 #include "p25/P25Utils.h"
@@ -86,6 +87,12 @@ bool NID::decode(const uint8_t* data)
     uint8_t nid[P25_NID_LENGTH_BYTES];
     P25Utils::decode(data, nid, 48U, 114U);
 
+    // handle digital "squelch" NAC
+    if ((m_nac == P25_NAC_DIGITAL_SQ) || (m_nac == P25_NAC_REUSE_RX_NAC)) {
+        uint32_t nac = ((nid[0U] << 4) + (nid[1U] >> 4)) & 0xFFFU;
+        createRxTxNID(nac); // bryanb: I hate this and it'll be slow
+    }
+
     uint32_t errs = P25Utils::compare(nid, m_rxTx[P25_DUID_LDU1], P25_NID_LENGTH_BYTES);
     if (errs < MAX_NID_ERRS) {
         m_duid = P25_DUID_LDU1;
@@ -136,7 +143,7 @@ bool NID::decode(const uint8_t* data)
 /// </summary>
 /// <param name="data"></param>
 /// <param name="duid"></param>
-void NID::encode(uint8_t* data, uint8_t duid) const
+void NID::encode(uint8_t* data, uint8_t duid)
 {
     assert(data != nullptr);
 
@@ -156,6 +163,11 @@ void NID::encode(uint8_t* data, uint8_t duid) const
         }
     }
     else {
+        // handle digital "squelch" NAC
+        if (m_nac == P25_NAC_DIGITAL_SQ) {
+            createRxTxNID(P25_DEFAULT_NAC);
+        }
+
         switch (duid) {
             case P25_DUID_HDU:
             case P25_DUID_TDU:
diff --git a/src/common/p25/NID.h b/src/common/p25/NID.h
index 6beda39f..6c1fd335 100644
--- a/src/common/p25/NID.h
+++ b/src/common/p25/NID.h
@@ -34,7 +34,7 @@ namespace p25
         /// <summary>Decodes P25 network identifier data.</summary>
         bool decode(const uint8_t* data);
         /// <summary>Encodes P25 network identifier data.</summary>
-        void encode(uint8_t* data, uint8_t duid) const;
+        void encode(uint8_t* data, uint8_t duid);
 
         /// <summary>Helper to configure a separate Tx NAC.</summary>
         void setTxNAC(uint32_t nac);
diff --git a/src/common/p25/P25Defines.h b/src/common/p25/P25Defines.h
index a7ba827f..b2aec8ad 100644
--- a/src/common/p25/P25Defines.h
+++ b/src/common/p25/P25Defines.h
@@ -186,6 +186,10 @@ namespace p25
 
     const uint32_t  P25_SID_STD_DEFAULT = 0x001U;
 
+    const uint32_t  P25_NAC_DIGITAL_SQ = 0xF7EU;
+    const uint32_t  P25_NAC_REUSE_RX_NAC = 0xF7FU;
+    const uint32_t  P25_DEFAULT_NAC = 0x293U;
+
     const uint32_t  P25_WUID_FNE = 0xFFFFFCU;
     const uint32_t  P25_WUID_REG = 0xFFFFFEU;
     const uint32_t  P25_WUID_ALL = 0xFFFFFFU;
diff --git a/src/common/p25/P25Utils.h b/src/common/p25/P25Utils.h
index 7e574f51..11a906cb 100644
--- a/src/common/p25/P25Utils.h
+++ b/src/common/p25/P25Utils.h
@@ -33,8 +33,8 @@ namespace p25
             if (nac < 0U) { // clamp to $000
                 nac = 0U;
             }
-            if (nac > 0xF7DU) { // clamp to $F7D
-                nac = 0xF7DU;
+            if (nac > 0xF7FU) { // clamp to $F7F
+                nac = 0xF7FU;
             }
 
             return nac;
diff --git a/src/host/Host.Config.cpp b/src/host/Host.Config.cpp
index b0755227..aaae172f 100644
--- a/src/host/Host.Config.cpp
+++ b/src/host/Host.Config.cpp
@@ -273,10 +273,10 @@ bool Host::readParams()
         m_dmrNetId = (uint32_t)::strtoul(rfssConfig["dmrNetId"].as<std::string>("1").c_str(), NULL, 16);
         m_dmrNetId = dmr::DMRUtils::netId(m_dmrNetId, dmr::SITE_MODEL_SMALL);
 
-        m_p25NAC = (uint32_t)::strtoul(rfssConfig["nac"].as<std::string>("293").c_str(), NULL, 16);
+        m_p25NAC = (uint32_t)::strtoul(rfssConfig["nac"].as<std::string>("F7E").c_str(), NULL, 16);
         m_p25NAC = p25::P25Utils::nac(m_p25NAC);
 
-        uint32_t p25TxNAC = (uint32_t)::strtoul(rfssConfig["txNAC"].as<std::string>("F7E").c_str(), NULL, 16);
+        uint32_t p25TxNAC = (uint32_t)::strtoul(rfssConfig["txNAC"].as<std::string>("293").c_str(), NULL, 16);
         if (p25TxNAC == m_p25NAC) {
             LogWarning(LOG_HOST, "Only use txNAC when split NAC operations are needed. nac and txNAC should not be the same!");
         }
@@ -318,7 +318,7 @@ bool Host::readParams()
         LogInfo("    DMR Network Id: $%05X", m_dmrNetId);
         LogInfo("    P25 NAC: $%03X", m_p25NAC);
 
-        if (p25TxNAC != 0xF7EU && p25TxNAC != m_p25NAC) {
+        if (p25TxNAC != p25::P25_NAC_DIGITAL_SQ && p25TxNAC != m_p25NAC) {
             LogInfo("    P25 Tx NAC: $%03X", p25TxNAC);
         }
 
@@ -630,7 +630,10 @@ bool Host::createModem()
             p25PostBWAdj, nxdnPostBWAdj, adfGainMode, afcEnable, afcKI, afcKP, afcRange);
         m_modem->setSoftPot(rxCoarse, rxFine, txCoarse, txFine, rssiCoarse, rssiFine);
         m_modem->setDMRColorCode(m_dmrColorCode);
-        m_modem->setP25NAC(m_p25NAC);
+        if (m_p25NAC == p25::P25_NAC_REUSE_RX_NAC)
+            m_modem->setP25NAC(p25::P25_NAC_DIGITAL_SQ);
+        else
+            m_modem->setP25NAC(m_p25NAC);
     }
 
     if (m_modemRemote) {