diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 43e60d6..339d546 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -7,7 +7,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        write_gran: [1, 8, 32, 64, 128]
+        write_gran: [1, 8, 32, 64, 128, 256]
     env:
       TEST_BSP_ROOT: ../AutoTestBsp
       UTEST_RUNNER_PATH: ../UtestRunner
diff --git a/inc/fdb_cfg_template.h b/inc/fdb_cfg_template.h
index f8bde78..ee96d92 100644
--- a/inc/fdb_cfg_template.h
+++ b/inc/fdb_cfg_template.h
@@ -34,7 +34,7 @@
 
 #ifdef FDB_USING_FAL_MODE
 /* the flash write granularity, unit: bit
- * only support 1(nor flash)/ 8(stm32f2/f4)/ 32(stm32f1)/ 64(stm32f7)/ 128(stm32h5) */
+ * only support 1(nor flash)/ 8(stm32f2/f4)/ 32(stm32f1)/ 64(stm32f7)/ 128(stm32h5)/ 256(stm32h7) */
 #define FDB_WRITE_GRAN                /* @note you must define it for a value */
 #endif
 
diff --git a/src/fdb_kvdb.c b/src/fdb_kvdb.c
index 56426b2..8559f52 100644
--- a/src/fdb_kvdb.c
+++ b/src/fdb_kvdb.c
@@ -27,8 +27,8 @@
 #error "Please configure flash write granularity (in fdb_cfg.h)"
 #endif
 
-#if FDB_WRITE_GRAN != 1 && FDB_WRITE_GRAN != 8 && FDB_WRITE_GRAN != 32 && FDB_WRITE_GRAN != 64 && FDB_WRITE_GRAN != 128
-#error "the write gran can be only setting as 1, 8, 32, 64 and 128"
+#if FDB_WRITE_GRAN != 1 && FDB_WRITE_GRAN != 8 && FDB_WRITE_GRAN != 32 && FDB_WRITE_GRAN != 64 && FDB_WRITE_GRAN != 128 && FDB_WRITE_GRAN != 256
+#error "the write gran can be only setting as 1, 8, 32, 64, 128 and 256"
 #endif
 
 /* magic word(`F`, `D`, `B`, `1`) */
@@ -109,6 +109,8 @@ struct sector_hdr_data {
     uint32_t reserved;
 #if (FDB_WRITE_GRAN == 64) || (FDB_WRITE_GRAN == 128)
     uint8_t padding[4];                          /**< align padding for 64bit and 128bit write granularity */
+#elif (FDB_WRITE_GRAN == 256)
+    uint8_t padding[20];                         /**< align padding for 256bit write granularity */
 #endif
 };
 typedef struct sector_hdr_data *sector_hdr_data_t;
@@ -122,9 +124,10 @@ struct kv_hdr_data {
     uint32_t value_len;                          /**< value length */
 #if (FDB_WRITE_GRAN == 64)
     uint8_t padding[4];                          /**< align padding for 64bit write granularity */
-#endif
-#if (FDB_WRITE_GRAN == 128)
-    uint8_t padding[12];                         /**< align padding for 128bit write granularity */
+#elif (FDB_WRITE_GRAN == 128)
+    uint8_t padding[12];                          /**< align padding for 128bit write granularity */
+#elif (FDB_WRITE_GRAN == 256)
+    uint8_t padding[15];                          /**< align padding for 256bit write granularity */
 #endif
 };
 typedef struct kv_hdr_data *kv_hdr_data_t;
diff --git a/tests/fdb_tsdb_tc.c b/tests/fdb_tsdb_tc.c
index a95701f..d7ceaef 100644
--- a/tests/fdb_tsdb_tc.c
+++ b/tests/fdb_tsdb_tc.c
@@ -46,6 +46,18 @@
 #define TEST_ITER1_SECTORS   5
 #define TEST_ITER1_COUNT     (TEST_ITER1_SECTORS * _TSIL_PER_SECTOR)
 
+/* TSLs per sector when blob is logbuf-sized string */
+#define _TSIL_LOGBUF_ALIGN_SZ  FDB_WG_ALIGN(sizeof(logbuf))
+#define _TSIL_PER_SECTOR_STR   ((TEST_SECTOR_SIZE - _TSIL_SEC_HDR_SZ) \
+                                / (_TSIL_IDX_DATA_SZ + _TSIL_LOGBUF_ALIGN_SZ))
+
+/* Cap at 256 to avoid timeout on small write granularities (e.g. gran=1/8/32),
+ * while still being dynamic enough to avoid ring-buffer wrap-around on large
+ * granularities (e.g. gran=64/128/256). */
+#define TEST_TS_COUNT          ((_TSIL_PER_SECTOR_STR * 14) < 256 \
+                                ? (_TSIL_PER_SECTOR_STR * 14) : 256)
+
+
 struct test_tls_data {
     int data;
     fdb_time_t time;
@@ -153,9 +165,14 @@ static void test_fdb_tsl_iter_by_time(void)
 static void test_fdb_tsl_query_count(void)
 {
     fdb_time_t from = 0, to = TEST_TS_COUNT * TEST_TIME_STEP;
+    uint32_t count;
 
     fdb_reboot();
-    uassert_true(fdb_tsl_query_count(&test_tsdb, from, to, FDB_TSL_WRITE) == TEST_TS_COUNT);
+    count = fdb_tsl_query_count(&test_tsdb, from, to, FDB_TSL_WRITE);
+    rt_kprintf("query_count from=%d to=%d => %u, expected=%u\n",
+               (int)from, (int)to, (unsigned)count, TEST_TS_COUNT);
+
+    uassert_true(count == TEST_TS_COUNT);
 }
 
 static bool est_fdb_tsl_set_status_cb(fdb_tsl_t tsl, void *arg)