From d393e0c30192611d4cac65a5429fd7180ce1f49c Mon Sep 17 00:00:00 2001
From: "info@mode42.com" <info@mode42.com>
Date: Fri, 7 Aug 2026 18:15:00 +0000
Subject: Initial push

---
 firmware/c1224/src/common/sense.c | 99 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 99 insertions(+)
 create mode 100644 firmware/c1224/src/common/sense.c

(limited to 'firmware/c1224/src/common/sense.c')

diff --git a/firmware/c1224/src/common/sense.c b/firmware/c1224/src/common/sense.c
new file mode 100644
index 0000000..6bd33a4
--- /dev/null
+++ b/firmware/c1224/src/common/sense.c
@@ -0,0 +1,99 @@
+/*
+ * Dual sense: CDT (Signal) + RXD packet heuristic (edges + HDLC 0x7E).
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+#include "sense.h"
+#include "board_pins.h"
+#include "config.h"
+#include "hardware/gpio.h"
+#include "pico/stdlib.h"
+#include <stdint.h>
+
+static bool g_signal;
+static bool g_packet;
+static bool g_flag;
+static absolute_time_t g_packet_until;
+static absolute_time_t g_window_start;
+static uint16_t g_edges;
+static bool g_last_rxd;
+static bool g_hold_valid;
+
+static void try_flag_sample(void)
+{
+    uint16_t sh = 0;
+    for (int i = 0; i < 16; i++) {
+        bool b = gpio_get(PIN_MODEM_RXD);
+        sh = (uint16_t)((sh << 1) | (b ? 1u : 0u));
+        if ((uint8_t)(sh & 0xFFu) == 0x7Eu) {
+            g_flag = true;
+            return;
+        }
+        sleep_us(833);
+    }
+}
+
+void sense_init(void)
+{
+    g_signal = false;
+    g_packet = false;
+    g_flag = false;
+    g_hold_valid = false;
+    g_window_start = get_absolute_time();
+    g_edges = 0;
+    g_last_rxd = gpio_get(PIN_MODEM_RXD);
+}
+
+void sense_poll(void)
+{
+    const c1224_config_t *cfg = config_get();
+
+    bool cdt = gpio_get(PIN_MODEM_CDT);
+    g_signal = cfg->cdt_active_high ? cdt : !cdt;
+
+    bool rxd = gpio_get(PIN_MODEM_RXD);
+    if (rxd != g_last_rxd) {
+        g_edges++;
+        g_last_rxd = rxd;
+    }
+
+    uint32_t win_ms = cfg->packet_window_ms ? cfg->packet_window_ms : 50;
+    if (absolute_time_diff_us(g_window_start, get_absolute_time()) >=
+        (int64_t)win_ms * 1000) {
+        if (g_edges >= cfg->packet_edge_min) {
+            g_flag = false;
+            try_flag_sample();
+            g_packet_until = make_timeout_time_ms(
+                cfg->packet_hold_ms ? cfg->packet_hold_ms : 500);
+            g_hold_valid = true;
+        }
+        g_edges = 0;
+        g_window_start = get_absolute_time();
+    }
+
+    if (g_hold_valid) {
+        if (time_reached(g_packet_until)) {
+            g_hold_valid = false;
+            g_packet = false;
+            g_flag = false;
+        } else {
+            g_packet = true;
+        }
+    } else {
+        g_packet = false;
+    }
+}
+
+bool sense_signal_active(void)
+{
+    return g_signal;
+}
+
+bool sense_packet_active(void)
+{
+    return g_packet;
+}
+
+bool sense_packet_flag(void)
+{
+    return g_flag;
+}
-- 
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