From 4e0dfecce038110a98b3b21b1e645b794913398d Mon Sep 17 00:00:00 2001
From: jess <jess@else-if.org>
Date: Tue, 31 Mar 2026 20:48:20 -0700
Subject: [PATCH] =?UTF-8?q?firmware:=20NVS-backed=20cell=20constant=20K=20?=
 =?UTF-8?q?=E2=80=94=20set/get=20over=20BLE=20for=20app=20sync?=
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Content-Transfer-Encoding: 8bit

---
 main/ble.c  | 15 +++++++++++++++
 main/ble.h  |  7 +++++++
 main/eis.c  | 30 ++++++++++++++++++++++++++++++
 main/eis.h  |  4 ++++
 main/eis4.c | 11 +++++++++++
 5 files changed, 67 insertions(+)

diff --git a/main/ble.c b/main/ble.c
index 1b31087..34b768b 100644
--- a/main/ble.c
+++ b/main/ble.c
@@ -186,10 +186,15 @@ static void parse_one_sysex(const uint8_t *midi, uint16_t mlen)
         cmd.clean.v_mv       = ble_decode_float(&midi[3]);
         cmd.clean.duration_s = ble_decode_float(&midi[8]);
         break;
+    case CMD_SET_CELL_K:
+        if (mlen < 8) return;
+        cmd.cell_k = ble_decode_float(&midi[3]);
+        break;
     case CMD_START_SWEEP:
     case CMD_GET_CONFIG:
     case CMD_STOP_AMP:
     case CMD_GET_TEMP:
+    case CMD_GET_CELL_K:
     case CMD_START_REFS:
     case CMD_GET_REFS:
     case CMD_CLEAR_REFS:
@@ -857,6 +862,16 @@ int ble_send_temp(float temp_c)
     return send_sysex(sx, p);
 }
 
+int ble_send_cell_k(float k)
+{
+    uint8_t sx[12];
+    uint16_t p = 0;
+    sx[p++] = 0xF0; sx[p++] = 0x7D; sx[p++] = RSP_CELL_K;
+    encode_float(k, &sx[p]); p += 5;
+    sx[p++] = 0xF7;
+    return send_sysex(sx, p);
+}
+
 int ble_send_ref_frame(uint8_t mode, uint8_t rtia_idx)
 {
     uint8_t sx[] = { 0xF0, 0x7D, RSP_REF_FRAME, mode & 0x7F, rtia_idx & 0x7F, 0xF7 };
diff --git a/main/ble.h b/main/ble.h
index 20bab11..5696dc0 100644
--- a/main/ble.h
+++ b/main/ble.h
@@ -20,6 +20,8 @@
 #define CMD_START_CLEAN   0x25
 #define CMD_OPEN_CAL      0x26
 #define CMD_CLEAR_OPEN_CAL 0x27
+#define CMD_SET_CELL_K    0x28
+#define CMD_GET_CELL_K    0x29
 #define CMD_START_REFS    0x30
 #define CMD_GET_REFS      0x31
 #define CMD_CLEAR_REFS    0x32
@@ -41,6 +43,7 @@
 #define RSP_CL_END      0x0E
 #define RSP_PH_RESULT   0x0F
 #define RSP_TEMP        0x10
+#define RSP_CELL_K      0x11
 #define RSP_REF_FRAME   0x20
 #define RSP_REF_LP_RANGE 0x21
 #define RSP_REFS_DONE   0x22
@@ -58,6 +61,7 @@ typedef struct {
         struct { float v_cond, t_cond_ms, v_free, v_total, t_dep_ms, t_meas_ms; uint8_t lp_rtia; } cl;
         struct { float stabilize_s; } ph;
         struct { float v_mv; float duration_s; } clean;
+        float cell_k;
     };
 } BleCommand;
 
@@ -103,6 +107,9 @@ int ble_send_ph_result(float v_ocp_mv, float ph, float temp_c);
 /* outbound: temperature */
 int ble_send_temp(float temp_c);
 
+/* outbound: cell constant */
+int ble_send_cell_k(float k);
+
 /* outbound: reference collection */
 int ble_send_ref_frame(uint8_t mode, uint8_t rtia_idx);
 int ble_send_ref_lp_range(uint8_t mode, uint8_t low_idx, uint8_t high_idx);
diff --git a/main/eis.c b/main/eis.c
index 30b0085..74a2ec0 100644
--- a/main/eis.c
+++ b/main/eis.c
@@ -23,6 +23,9 @@ static struct {
     uint32_t dertia_reg;
 } ctx;
 
+/* cell constant K (cm⁻¹), cached from NVS */
+static float cell_k_cached;
+
 /* open-circuit calibration data */
 static struct {
     fImpCar_Type y[EIS_MAX_POINTS]; /* admittance at each freq */
@@ -585,3 +588,30 @@ int eis_has_open_cal(void)
 {
     return ocal.valid;
 }
+
+#define NVS_CELLK_KEY "cell_k"
+
+void eis_set_cell_k(float k)
+{
+    cell_k_cached = k;
+    nvs_handle_t h;
+    if (nvs_open(NVS_OCAL_NS, NVS_READWRITE, &h) != ESP_OK) return;
+    nvs_set_blob(h, NVS_CELLK_KEY, &k, sizeof(k));
+    nvs_commit(h);
+    nvs_close(h);
+}
+
+float eis_get_cell_k(void)
+{
+    return cell_k_cached;
+}
+
+void eis_load_cell_k(void)
+{
+    nvs_handle_t h;
+    if (nvs_open(NVS_OCAL_NS, NVS_READONLY, &h) != ESP_OK) return;
+    size_t len = sizeof(cell_k_cached);
+    if (nvs_get_blob(h, NVS_CELLK_KEY, &cell_k_cached, &len) != ESP_OK || len != sizeof(cell_k_cached))
+        cell_k_cached = 0.0f;
+    nvs_close(h);
+}
diff --git a/main/eis.h b/main/eis.h
index 4348c75..c4cd28c 100644
--- a/main/eis.h
+++ b/main/eis.h
@@ -63,4 +63,8 @@ void eis_clear_open_cal(void);
 int  eis_has_open_cal(void);
 void eis_load_open_cal(void);
 
+void  eis_set_cell_k(float k);
+float eis_get_cell_k(void);
+void  eis_load_cell_k(void);
+
 #endif
diff --git a/main/eis4.c b/main/eis4.c
index 383c491..4b94641 100644
--- a/main/eis4.c
+++ b/main/eis4.c
@@ -56,6 +56,7 @@ void app_main(void)
 
     eis_default_config(&cfg);
     eis_load_open_cal();
+    eis_load_cell_k();
     temp_init();
 
     esp_netif_init();
@@ -207,6 +208,16 @@ void app_main(void)
             printf("Open-circuit cal cleared\n");
             break;
 
+        case CMD_SET_CELL_K:
+            eis_set_cell_k(cmd.cell_k);
+            ble_send_cell_k(cmd.cell_k);
+            printf("Cell K set: %.4f cm^-1\n", cmd.cell_k);
+            break;
+
+        case CMD_GET_CELL_K:
+            ble_send_cell_k(eis_get_cell_k());
+            break;
+
         case CMD_START_CL: {
             ClConfig cl_cfg;
             cl_cfg.v_cond    = cmd.cl.v_cond;