diff --git a/Production/Firmware/musec_pico.uf2 b/Production/Firmware/musec_pico.uf2
index 0f06d17..27a0f99 100644
Binary files a/Production/Firmware/musec_pico.uf2 and b/Production/Firmware/musec_pico.uf2 differ
diff --git a/firmware/src/board_defs.h b/firmware/src/board_defs.h
index f81077b..0ca745a 100644
--- a/firmware/src/board_defs.h
+++ b/firmware/src/board_defs.h
@@ -12,7 +12,8 @@
 #define BUS_I2C i2c0
 #define BUS_I2C_SDA 0
 #define BUS_I2C_SCL 1
-#define BUS_I2C_FREQ 266*1000
+#define BUS_I2C_FREQ 166*1000
+#define BUS_I2C_FAST_FREQ 400*1000
 
 #define SPIN_DEF { 13, 12, 11, 10, 9 }
  
diff --git a/firmware/src/commands.c b/firmware/src/commands.c
index 2590084..76a25af 100644
--- a/firmware/src/commands.c
+++ b/firmware/src/commands.c
@@ -27,11 +27,12 @@ static void disp_light()
 static void disp_spin()
 {
     printf("[Spin]\n");
+    printf("  Fast I2C: %s.\n", musec_cfg->spin.fast_i2c ? "ON" : "OFF");
     printf("  Units Per Turn: %d.\n", musec_cfg->spin.units_per_turn);
     for (int i = 0; i < 5; i++) {
         printf("  Spinner %d: %s, %s.\n", i + 1,
                spin_present(i) ? "OK" : "ERROR",
-               musec_cfg->spin.reversed[i] ? "Reversed" : "Forward");
+               musec_cfg->spin.reversed & (1 << i) ? "Reversed" : "Forward");
     }
 }
 
@@ -137,15 +138,36 @@ static void handle_spin_invert(int id, const char *dir)
         return;
     }
 
-    musec_cfg->spin.reversed[id] = match;
+    if (match == 0) {
+        musec_cfg->spin.reversed &= ~(1 << id);
+    } else if (match == 1) {
+        musec_cfg->spin.reversed |= (1 << id);
+    }
 
     config_changed();
     disp_spin();
 }
 
+static void handle_i2c_option(const char *option)
+{
+    const char *usage = "Usage: spin fast_i2c <on|off>\n";
+    const char *choices[] = {"off", "on"};
+    int match = cli_match_prefix(choices, count_of(choices), option);
+    if (match < 0) {
+        printf(usage);
+        return;
+    }
+
+    musec_cfg->spin.fast_i2c = match;
+    save_request(true); // immediate save
+    disp_spin();
+    printf("Note: Please reboot the device to apply I2C speed change.\n");
+}
+
 static void handle_spin(int argc, char *argv[])
 {
     const char *usage = "Usage: spin rate <units_per_turn>\n"
+                        "       spin fast_i2c <on|off>\n"
                         "       spin <id> <normal|reverse>\n"
                         "  units_per_turn: 20..255\n"
                         "  id: 1..5\n";
@@ -154,7 +176,7 @@ static void handle_spin(int argc, char *argv[])
         return;
     }
 
-    const char *choices[] = { "1", "2", "3", "4", "5", "rate" };
+    const char *choices[] = { "1", "2", "3", "4", "5", "fast_i2c", "rate" };
     int match = cli_match_prefix(choices, count_of(choices), argv[0]);
     if (match < 0) {
         printf(usage);
@@ -162,6 +184,10 @@ static void handle_spin(int argc, char *argv[])
     }
 
     if (match == 5) {
+        handle_i2c_option(argv[1]);
+        return;
+    }
+    if (match == 6) {
         handle_spin_rate(argv[1]);
         return;
     }
diff --git a/firmware/src/config.c b/firmware/src/config.c
index a6c38de..2398cde 100644
--- a/firmware/src/config.c
+++ b/firmware/src/config.c
@@ -13,6 +13,7 @@ musec_cfg_t *musec_cfg;
 
 static musec_cfg_t default_cfg = {
     .spin = {
+        .fast_i2c = false,
         .units_per_turn = 80,
     },
     .light = {
diff --git a/firmware/src/config.h b/firmware/src/config.h
index 5649c01..012e3f6 100644
--- a/firmware/src/config.h
+++ b/firmware/src/config.h
@@ -17,7 +17,9 @@ typedef struct {
 typedef struct __attribute__((packed)) {
     struct {
         uint8_t units_per_turn;
-        uint8_t reversed[5];
+        bool fast_i2c;
+        uint8_t reversed;
+        uint8_t reserved[3];
     } spin;
     struct {
         bool internal;
diff --git a/firmware/src/spin.c b/firmware/src/spin.c
index e5ababa..4f47ac6 100644
--- a/firmware/src/spin.c
+++ b/firmware/src/spin.c
@@ -31,7 +31,12 @@ void spin_init()
     gpio_init(BUS_I2C_SCL);
     gpio_set_function(BUS_I2C_SCL, GPIO_FUNC_I2C);
     gpio_pull_up(BUS_I2C_SCL);
-    i2c_init(BUS_I2C, BUS_I2C_FREQ);
+
+    if (musec_cfg->spin.fast_i2c) {
+        i2c_init(BUS_I2C, BUS_I2C_FAST_FREQ);
+    } else {
+        i2c_init(BUS_I2C, BUS_I2C_FREQ);
+    }
 
     for (int i = 0; i < SPIN_NUM; i++) {
         uint8_t ce = spin_enablers[i];
@@ -66,19 +71,21 @@ static uint16_t spin_reading[SPIN_NUM];
 
 void spin_update()
 {
-    static bool flip = false;
-    flip = !flip;
+    static int count = 0;
 
     for (int i = 0; i < SPIN_NUM; i++) {
-        if (flip ^ (i % 2)) {
+        if (!musec_cfg->spin.fast_i2c && (i != count)) {
             continue;
         }
+
         tmag5273_use(i);
         spin_reading[i] = tmag5273_read_angle();
-        if (musec_cfg->spin.reversed[i]) {
+        if (musec_cfg->spin.reversed & (1 << i)) {
             spin_reading[i] = FULL_SCALE - spin_reading[i];
         }
     }
+
+    count = (count + 1) % SPIN_NUM;
 }
 
 uint16_t spin_read(uint8_t index)