diff --git a/Attic/attitude.c b/Attic/attitude.c
deleted file mode 100644
index 92bc73f..0000000
--- a/Attic/attitude.c
+++ /dev/null
@@ -1,128 +0,0 @@
-#include "attitude.h"
-#include "util.h"
-#include <stdio.h>
-
-struct dcm dcm = {
-    .matrix    = MAT3_IDENTITY,
-    .down_ref  = { 0,  0, -1 },
-    .north_ref = { 1,  0,  0 },
-/*
-    .acc_kp = 1, .acc_ki = 0.001,
-    .mag_kp = 0, .mag_ki = 0
-*/
-};
-
-
-/**
- * Apply an infinitesimal rotation w*dt to a direction cosine matrix A.
- * An orthonormalization step is added to prevent rounding errors.
- *
- * Without the normalization, this would be a simple matrix multiplication:
- *
- * return mat3_matmul( A, (mat3f) {
- *        1,   -w.z,  w.y,
- *      w.z,    1, -w.x,
- *     -w.y,  w.x,    1
- * };
- */
-static mat3f dcm_integrate(mat3f A, vec3f w, float dt)
-{
-    w = vec3f_scale(w, dt);
-
-    // Calculate the new x and y axes. z is calculated later.
-    //
-    vec3f x = vec3f_matmul(A, (vec3f){    1, w.z, -w.y } );
-    vec3f y = vec3f_matmul(A, (vec3f){ -w.z,   1,  w.x } );
-
-    // Orthonormalization
-    //
-    // First we compute the dot product of the x and y rows of the matrix, which
-    // is supposed to be zero, so the result is a measure of how much the X and Y
-    // rows are rotating toward each other
-    //
-    float error = vec3f_dot(x, y);
-
-    // We apportion half of the error each to the x and y rows, and approximately
-    // rotate the X and Y rows in the opposite direction by cross coupling:
-    //
-    vec3f xo, yo, zo;
-    xo = vec3f_sub(x, vec3f_scale(y, 0.5 * error));
-    yo = vec3f_sub(y, vec3f_scale(x, 0.5 * error));
-
-    // Scale them to unit length and take a cross product for the Z axis
-    //
-    xo = vec3f_norm_fast(xo);
-    yo = vec3f_norm_fast(yo);
-    zo = vec3f_cross(xo, yo);
-
-    return (mat3f) {
-        xo.x, yo.x, zo.x,
-        xo.y, yo.y, zo.y,
-        xo.z, yo.z, zo.z
-    };
-}
-
-
-extern void dcm_update(vec3f gyro, vec3f acc, float dt)
-{
-    dcm.offset_p = vec3f_zero;
-
-    // Apply accelerometer correction
-    //
-    vec3f down  = vec3f_matmul(dcm.matrix, vec3f_norm_fast(acc));
-    vec3f error = vec3f_cross(down, dcm.down_ref);
-
-    dcm.debug = error;
-
-    dcm.offset_p = vec3f_add(dcm.offset_p, vec3f_scale(error, dcm.acc_kp));
-    dcm.offset_i = vec3f_add(dcm.offset_i, vec3f_scale(error, dcm.acc_ki));
-
-    // todo: magnetometer correction, once we have one
-
-    // Calculate drift-corrected roll, pitch and yaw angles
-    //
-    dcm.omega = gyro;
-    dcm.omega = vec3f_add(dcm.omega, dcm.offset_p);
-    dcm.omega = vec3f_add(dcm.omega, dcm.offset_i);
-
-    // Apply rotation to the direction cosine matrix
-    //
-    dcm.matrix = dcm_integrate(dcm.matrix, dcm.omega, dt);
-    dcm.euler = mat3f_to_euler(dcm.matrix);
-}
-
-
-void  dcm_reset(void)
-{
-    dcm.matrix   = mat3f_identity;
-    dcm.euler    = vec3f_zero;
-    dcm.omega    = vec3f_zero;
-    dcm.offset_p = vec3f_zero;
-    dcm.offset_i = vec3f_zero;
-}
-
-// -----
-#include <string.h>
-
-
-void cmd_dcm_show(void)
-{
-    struct dcm d;
-    ATOMIC_COPY(&d, &dcm, sizeof(d));
-
-    printf("                x/roll    y/pitch      z/yaw\n");
-    printf("down_ref  : %10.4f %10.4f %10.4f\n", d.down_ref.x, d.down_ref.y, d.down_ref.z);
-    printf("north_ref : %10.4f %10.4f %10.4f\n", d.north_ref.x, d.north_ref.y, d.north_ref.z);
-    printf("\n");
-    printf("offset_p  : %10.4f %10.4f %10.4f\n", d.offset_p.x, d.offset_p.y, d.offset_p.z);
-    printf("offset_i  : %10.4f %10.4f %10.4f\n", d.offset_i.x, d.offset_i.y, d.offset_i.z);
-    printf("\n");
-    printf("dcm_omega : %10.4f %10.4f %10.4f\n", d.omega.x, d.omega.y, d.omega.z);
-    printf("dcm_euler : %10.4f %10.4f %10.4f\n", d.euler.x, d.euler.y, d.euler.z);
-    printf("\n");
-    printf("dcm_matrix: %10.4f %10.4f %10.4f\n", d.matrix.m00, d.matrix.m01, d.matrix.m02);
-    printf("            %10.4f %10.4f %10.4f\n", d.matrix.m10, d.matrix.m11, d.matrix.m12);
-    printf("            %10.4f %10.4f %10.4f\n", d.matrix.m20, d.matrix.m21, d.matrix.m22);
-    printf("\n");
-    printf("debug     : %10.4f %10.4f %10.4f\n", d.debug.x, d.debug.y, d.debug.z);
-}
diff --git a/Attic/attitude.h b/Attic/attitude.h
deleted file mode 100644
index f84ad04..0000000
--- a/Attic/attitude.h
+++ /dev/null
@@ -1,32 +0,0 @@
-#ifndef ATTITUDE_H
-#define ATTITUDE_H
-
-#include "matrix3f.h"
-
-struct dcm {
-    mat3f matrix;       ///< current direction cosine matrix
-    vec3f euler;        ///< roll, pitch and yaw angles
-    vec3f omega;        ///< drift corrected angular rates
-
-    vec3f offset_p;     ///< drift correction p-term
-    vec3f offset_i;     ///< drift correction i-term
-
-    vec3f down_ref;     ///< accelerometer "down" reference
-    float acc_kp;       ///< accelerometer p gain
-    float acc_ki;       ///< accelerometer i gain
-
-    vec3f north_ref;    ///< magnetometer "north" reference
-    float mag_kp;       ///< magnetometer p gain
-    float mag_ki;       ///< magnetometer i gain
-
-    vec3f debug;
-};
-
-extern struct dcm dcm;
-
-extern void dcm_update(vec3f gyro, vec3f acc, float dt);
-extern void dcm_reset(void);
-
-extern void cmd_dcm_show(void);
-
-#endif
diff --git a/Makefile b/Makefile
index 7d0dc6f..f879368 100644
--- a/Makefile
+++ b/Makefile
@@ -207,6 +207,7 @@ CFLAGS += -ffunction-sections
 CFLAGS += -fdata-sections
 CFLAGS += -Wall
 CFLAGS += -Wstrict-prototypes
+CFLAGS += -Wsign-compare
 #CFLAGS += -Wextra
 #CFLAGS += -Wpointer-arith
 #CFLAGS += -Winline
diff --git a/Source/attitude.c b/Source/attitude.c
index 31e6123..28cec1d 100644
--- a/Source/attitude.c
+++ b/Source/attitude.c
@@ -1,5 +1,6 @@
 #include "attitude.h"
 #include "util.h"
+#include "sensors.h"
 #include <stdio.h>
 
 struct dcm dcm = {
@@ -63,13 +64,13 @@ static mat3f dcm_integrate(mat3f A, vec3f w, float dt)
 }
 
 
-extern void dcm_update(vec3f gyro, vec3f acc, float dt)
+extern void dcm_update(struct sensor_data *sensor, float dt)
 {
     dcm.offset_p = vec3f_zero;
 
     // Apply accelerometer correction
     //
-    vec3f down  = vec3f_matmul(dcm.matrix, vec3f_norm(acc));
+    vec3f down  = vec3f_matmul(dcm.matrix, vec3f_norm(sensor->acc));
     vec3f error = vec3f_cross(down, dcm.down_ref);
 
     dcm.debug = error;
@@ -81,7 +82,7 @@ extern void dcm_update(vec3f gyro, vec3f acc, float dt)
 
     // Calculate drift-corrected roll, pitch and yaw angles
     //
-    dcm.omega = gyro;
+    dcm.omega = sensor->gyro;
     dcm.omega = vec3f_add(dcm.omega, dcm.offset_p);
     dcm.omega = vec3f_add(dcm.omega, dcm.offset_i);
 
@@ -103,12 +104,13 @@ void  dcm_reset(void)
 
 // -----
 #include <string.h>
+#include "command.h"
 
 
-void cmd_dcm_show(void)
+static void cmd_dcm_show(void)
 {
     struct dcm d;
-    ATOMIC_COPY(&d, &dcm, sizeof(d));
+    memcpy(&d, &dcm, sizeof(d));
 
     printf("                x/roll    y/pitch      z/yaw\n");
     printf("down_ref  : %10.4f %10.4f %10.4f\n", d.down_ref.x, d.down_ref.y, d.down_ref.z);
@@ -126,3 +128,5 @@ void cmd_dcm_show(void)
     printf("\n");
     printf("debug     : %10.4f %10.4f %10.4f\n", d.debug.x, d.debug.y, d.debug.z);
 }
+
+SHELL_CMD(dcm_show, (cmdfunc_t)cmd_dcm_show, "show dcm values")
diff --git a/Source/attitude.h b/Source/attitude.h
index 5fc786f..e7460d0 100644
--- a/Source/attitude.h
+++ b/Source/attitude.h
@@ -1,6 +1,7 @@
 #pragma once
 
 #include "matrix3f.h"
+#include "sensors.h"
 
 struct dcm {
     mat3f matrix;       ///< current direction cosine matrix
@@ -23,8 +24,5 @@ struct dcm {
 
 extern struct dcm dcm;
 
-extern void dcm_update(vec3f gyro, vec3f acc, float dt);
+extern void dcm_update(struct sensor_data *sensor, float dt);
 extern void dcm_reset(void);
-
-extern void cmd_dcm_show(void);
-
diff --git a/Source/dma_io_driver.c b/Source/dma_io_driver.c
index 0d5b965..53c5d7c 100644
--- a/Source/dma_io_driver.c
+++ b/Source/dma_io_driver.c
@@ -42,7 +42,7 @@ void DMA2_Stream7_IRQHandler(void)
     uint16_t tim7_cnt = TIM7->CNT;
     uint32_t hisr = DMA2->HISR;
 
-    const int len_2 = DMA_IO_RX_SIZE / 2;
+    const unsigned int len_2 = DMA_IO_RX_SIZE / 2;
     const uint8_t mask = ~dma_tx_ws2812_bits;
 
     if (hisr & DMA_HISR_HTIF7) {
diff --git a/Source/dma_io_servo_in.c b/Source/dma_io_servo_in.c
index 4a389d2..e3b415f 100644
--- a/Source/dma_io_servo_in.c
+++ b/Source/dma_io_servo_in.c
@@ -20,7 +20,7 @@ static void edge(uint32_t t, int ch, int rising)
 }
 
 
-void dma_io_decode_servo(const void *dma_buf, int dma_len, uint8_t mask)
+void dma_io_decode_servo(const void *dma_buf, unsigned int dma_len, uint8_t mask)
 {
     // TODO: filter edges
     // TODO: detect timeouts
@@ -31,12 +31,12 @@ void dma_io_decode_servo(const void *dma_buf, int dma_len, uint8_t mask)
     const uint32_t *src = dma_buf;
     uint32_t  mask32 = (mask<<24) | (mask<<16) | (mask<<8) | mask;
 
-    for (int i=0; i < dma_len / 4; i++) {
+    for (unsigned int i=0; i < dma_len / 4; i++) {
         uint32_t state = *src++ & mask32;
         uint32_t diff  = last_state ^ state;
 
         if (diff) {
-            for (int j=0; j<32; j++) {
+            for (unsigned int j=0; j<32; j++) {
                 if (diff & (1UL << j))
                     edge(t + (j>>3), j & 7, state & (1UL << j));
             }
diff --git a/Source/dma_io_servo_in.h b/Source/dma_io_servo_in.h
index a403c13..7d26d1b 100644
--- a/Source/dma_io_servo_in.h
+++ b/Source/dma_io_servo_in.h
@@ -12,7 +12,6 @@ extern struct dma_io_servo_in dma_io_servo_in[8];
 
 
 void dma_io_decode_servo(
-    const void *dma_buf, int dma_len, uint8_t mask
+    const void *dma_buf, unsigned int dma_len, uint8_t mask
 
 );
-
diff --git a/Source/dma_io_servo_out.h b/Source/dma_io_servo_out.h
index daa172d..1779d76 100644
--- a/Source/dma_io_servo_out.h
+++ b/Source/dma_io_servo_out.h
@@ -3,7 +3,6 @@
 #include <stdint.h>
 
 void dma_io_set_servo(
-    void *dma_buf, int dma_len, uint8_t mask,
+    void *dma_buf, unsigned int dma_len, uint8_t mask,
     int t_pulse
 );
-
diff --git a/Source/filter.c b/Source/filter.c
index c3ffca1..f0c22f2 100644
--- a/Source/filter.c
+++ b/Source/filter.c
@@ -142,7 +142,7 @@ void avg_reset(struct avg_filter *f, int32_t x)
 {
     f->index = 0;
     f->acc   = x * f->size;
-    for (int i=0; i<f->size; i++)
+    for (uint32_t i=0; i<f->size; i++)
         f->buf[i] = x;
 }
 
diff --git a/Source/flight_ctrl.c b/Source/flight_ctrl.c
index 378d7fc..feffb50 100644
--- a/Source/flight_ctrl.c
+++ b/Source/flight_ctrl.c
@@ -3,6 +3,7 @@
 #include "bldc_task.h"
 #include "rc_input.h"
 #include "util.h"
+#include "attitude.h"
 
 #include "FreeRTOS.h"
 #include "task.h"
@@ -11,16 +12,41 @@
 static struct sensor_data   sensor_data;
 static struct rc_input      rc_input;
 
-struct pid_ctrl   pid_pitch = { .kp = 1, .ki = 0, .kd = 0, .min = -5, .max = 5, .dt = 1e-3 };
-struct pid_ctrl   pid_roll  = { .kp = 1, .ki = 0, .kd = 0, .min = -5, .max = 5, .dt = 1e-3 };
-struct pid_ctrl   pid_yaw   = { .kp = 1, .ki = 0, .kd = 0, .min = -5, .max = 5, .dt = 1e-3 };
+struct pid_ctrl pid_pitch = { .min = -5, .max = 5, .dt = 1e-3 };
+struct pid_ctrl pid_roll  = { .min = -5, .max = 5, .dt = 1e-3 };
+struct pid_ctrl pid_yaw   = { .min = -5, .max = 5, .dt = 1e-3 };
 
-float   rc_pitch, rc_roll, rc_yaw, rc_thrust;
+float rc_pitch, rc_roll, rc_yaw, rc_thrust;
 
-float foo = 1;
-float bar = 0;
-float baz = 0;
+float pid_p = 1;
+float pid_i = 0;
+float pid_d = 0;
+uint8_t fc_state = 0;
 
+/*
+void systick_handler(void)
+{
+    dcm_update(
+    sensor_data.gyro,
+    sensor_data.acc,
+    1.0 / SYSTICK_FREQ
+    );
+
+    flt_pid_update(&pid_pitch, (rc_pitch - dcm.euler.x), 0);
+    flt_pid_update(&pid_roll , (rc_roll  - dcm.euler.y), 0);
+    flt_pid_update(&pid_yaw  , (rc_yaw   - dcm.euler.z), 0);
+
+    int pwm_front = rc_thrust + pid_pitch.out + pid_yaw.out;
+    int pwm_back  = rc_thrust - pid_pitch.out + pid_yaw.out;
+    int pwm_left  = rc_thrust + pid_roll.out  - pid_yaw.out;
+    int pwm_right = rc_thrust - pid_roll.out  - pid_yaw.out;
+
+    motor[ID_FRONT].pwm = clamp(pwm_front, 32, 400);
+    motor[ID_BACK ].pwm = clamp(pwm_back , 32, 400);
+    motor[ID_LEFT ].pwm = clamp(pwm_left , 32, 400);
+    motor[ID_RIGHT].pwm = clamp(pwm_right, 32, 400);
+}
+*/
 void flight_ctrl(void *pvParameters)
 {
     //uint32_t t0 = xTaskGetTickCount();
@@ -32,8 +58,11 @@ void flight_ctrl(void *pvParameters)
 
     vTaskDelay(1000);
 
-    int ok = 0;
-    int old_ok = 0;
+    uint8_t ok = 0;
+    uint8_t old_ok = 0;
+    uint8_t stop_once = 0;
+
+    dcm_reset();
 
     for (;;) {
         sensor_read(&sensor_data);
@@ -60,23 +89,31 @@ void flight_ctrl(void *pvParameters)
             ok = 0;
         }
 
-        pid_pitch.kp = foo;
-        pid_roll.kp = foo;
-        pid_yaw.kp = foo;
-
-        pid_pitch.ki = bar;
-        pid_roll.ki = bar;
-        pid_yaw.ki = bar;
+        if (fc_state & 1) {
+            pid_pitch.kp = pid_p;
+            pid_roll .kp = pid_p;
+            pid_yaw  .kp = pid_p;
 
-        pid_pitch.kd = baz;
-        pid_roll.kd = baz;
-        pid_yaw.kd = baz;
+            pid_pitch.ki = pid_i;
+            pid_roll .ki = pid_i;
+            pid_yaw  .ki = pid_i;
 
-        pid_update(&pid_pitch, (rc_pitch - sensor_data.gyro.x), 0);
-        pid_update(&pid_roll , (rc_roll  + sensor_data.gyro.y), 0);
-        pid_update(&pid_yaw  , (rc_yaw   + sensor_data.gyro.z), 0);
+            pid_pitch.kd = pid_d;
+            pid_roll .kd = pid_d;
+            pid_yaw  .kd = pid_d;
+        }
 
+        if (fc_state & 2 || !(rc_input.channels[5] < 1500)) {
+                dcm_update(&sensor_data, 1e-3);
 
+                pid_update(&pid_pitch, (rc_pitch - dcm.euler.x), 0);
+                pid_update(&pid_roll , (rc_roll  + dcm.euler.y), 0);
+                pid_update(&pid_yaw  , (rc_yaw   + dcm.euler.z), 0);
+        } else {
+                pid_update(&pid_pitch, (rc_pitch - sensor_data.gyro.x), 0);
+                pid_update(&pid_roll , (rc_roll  + sensor_data.gyro.y), 0);
+                pid_update(&pid_yaw  , (rc_yaw   + sensor_data.gyro.z), 0);
+        }
         if (ok) {
             bldc_state.motors[ID_FL].u_d = clamp(rc_thrust + pid_pitch.u - pid_roll.u - pid_yaw.u, 1, 10);
             bldc_state.motors[ID_FR].u_d = clamp(rc_thrust + pid_pitch.u + pid_roll.u + pid_yaw.u, 1, 10);
@@ -89,12 +126,14 @@ void flight_ctrl(void *pvParameters)
                 bldc_state.motors[ID_RL].state = STATE_START;
                 bldc_state.motors[ID_RR].state = STATE_START;
             }
+            stop_once = 0;
         }
-        else {
+        else if (!stop_once) {
             bldc_state.motors[ID_FL].state = STATE_STOP;
             bldc_state.motors[ID_FR].state = STATE_STOP;
             bldc_state.motors[ID_RL].state = STATE_STOP;
             bldc_state.motors[ID_RR].state = STATE_STOP;
+            stop_once = 1;
         }
 
         old_ok = ok;
diff --git a/Source/flight_ctrl.h b/Source/flight_ctrl.h
index 5dd63df..25a9270 100644
--- a/Source/flight_ctrl.h
+++ b/Source/flight_ctrl.h
@@ -2,3 +2,7 @@
 
 
 void flight_ctrl(void *pvParameters);
+
+
+extern float pid_p, pid_i, pid_d;
+extern struct pid_ctrl pid_pitch, pid_roll, pid_yaw;
diff --git a/Source/param_table.c b/Source/param_table.c
index e67521e..d928ccb 100644
--- a/Source/param_table.c
+++ b/Source/param_table.c
@@ -7,11 +7,11 @@
 #include "rc_ppm.h"
 #include "dma_io_driver.h"
 #include "sensors.h"
+#include "flight_ctrl.h"
+#include "attitude.h"
 
 static int board_address;
 
-extern float foo, bar, baz;
-
 const struct param_info  param_table[] = {
     {    1, P_INT32(&board_address    ), READONLY, .name = "board_address" },
     {    4, P_INT32((int*)&warnings.w ), NOEEPROM, .name = "warning_flags" },
@@ -96,9 +96,68 @@ const struct param_info  param_table[] = {
             .help = "PPM sum signal synchronization pulse width"
     },
 
-    { 300, P_FLOAT(&foo) },
-    { 301, P_FLOAT(&bar) },
-    { 302, P_FLOAT(&baz) },
+    {  300, P_FLOAT(&pid_p, 1, 0 , 10),
+       .name = "pid_p",
+       .help = "all gyro PID P Part"
+    },
+    {  301, P_FLOAT(&pid_i, 0, 0, 10),
+       .name = "pid_i",
+       .help = "all gyro PID I Part"
+    },
+    {  302, P_FLOAT(&pid_d, 0, 0, 10),
+       .name = "pid_d",
+       .help = "all gyro PID D Part"
+    },
+
+
+    {  310, P_FLOAT(&pid_pitch.kp, 1, 0, 10),
+       .name = "pid_pitch.kp",
+       .help = "gyro pitch PID P Part"
+    },
+    {  311, P_FLOAT(&pid_pitch.ki, 0, 0 ,10),
+       .name = "pid_pitch.ki",
+       .help = "gyro pitch PID I Part"
+    },
+    {  312, P_FLOAT(&pid_pitch.kd, 0, 0, 10),
+       .name = "pid_pitch.kd",
+       .help = "gyro pitch PID D Part"
+    },
+
+    {  320, P_FLOAT(&pid_roll.kp, 1, 0, 10),
+        .name = "pid_roll.kp",
+        .help = "gyro roll PID P Part"
+    },
+    {  321, P_FLOAT(&pid_roll.ki, 0, 0, 10),
+        .name = "pid_roll.ki",
+        .help = "gyro roll PID I Part"
+    },
+    {  322, P_FLOAT(&pid_roll.kd, 0, 0, 10),
+        .name = "pid_roll.kd",
+        .help = "gyro roll PID D Part"
+    },
+
+    {  330, P_FLOAT(&pid_yaw.kp, 1, 0, 10),
+        .name = "pid_yaw.kp",
+        .help = "gyro yaw PID P Part"
+    },
+    {  331, P_FLOAT(&pid_yaw.ki, 0, 0, 10),
+        .name = "pid_yaw.ki",
+        .help = "gyro yaw PID I Part"
+    },
+    {  332, P_FLOAT(&pid_yaw.kd, 0, 0, 10),
+        .name = "pid_yaw.kd",
+        .help = "gyro yaw PID D Part"
+    },
+
+    {  360, P_FLOAT(&dcm.acc_kp, 0, 0, 10),
+        .name = "dcm.acc_kp",
+        .help = "DCM acc P Part"
+    },
+
+    {  361, P_FLOAT(&dcm.acc_ki, 0, 0, 10),
+       .name = "dcm.acc_ki",
+       .help = "DCM acc I Part"
+    },
 
     // Debug DAC outputs
     //
diff --git a/Source/rc_input.c b/Source/rc_input.c
index f15657b..26481ed 100644
--- a/Source/rc_input.c
+++ b/Source/rc_input.c
@@ -76,7 +76,7 @@ static void cmd_rc_show(void)
         rc_strmode(rc_config.mode), rc.valid, rc.rssi, rc.num_channels
     );
 
-    for (int i=0; i<RC_MAX_CHANNELS; i++) {
+    for (unsigned int i=0; i<RC_MAX_CHANNELS; i++) {
         char bar[31];
         strnbar(bar, sizeof(bar), rc.channels[i], 1000, 2000);
 
diff --git a/Source/sensors.c b/Source/sensors.c
index 430fcbf..bf8010d 100644
--- a/Source/sensors.c
+++ b/Source/sensors.c
@@ -211,7 +211,7 @@ static void cmd_sensor_show(int argc, char *argv[])
             break;
 
         case MODE_CSV:
-             for (int i=0; i<ARRAY_SIZE(values); i++) {
+             for (unsigned int i=0; i<ARRAY_SIZE(values); i++) {
                  if (d.clipflags & (1<<i))
                      printf(ANSI_BG_RED);
 
@@ -224,7 +224,7 @@ static void cmd_sensor_show(int argc, char *argv[])
              break;
 
         case MODE_RAW:
-            for (int i=0; i<ARRAY_SIZE(values); i++) {
+            for (unsigned int i=0; i<ARRAY_SIZE(values); i++) {
                 uint32_t i32;
                 memcpy(&i32, &values[i], 4);
                 printf("%08lx", i32);
diff --git a/Source/syscalls.c b/Source/syscalls.c
index 50a8e09..b24d51e 100644
--- a/Source/syscalls.c
+++ b/Source/syscalls.c
@@ -29,7 +29,7 @@ struct device_info  device_table[16];
 
 int dev_register(const char *name, const struct file_ops *ops)
 {
-    for (int i=0; i<ARRAY_SIZE(device_table); i++) {
+    for (unsigned int i=0; i<ARRAY_SIZE(device_table); i++) {
         if (!device_table[i].name) {
             device_table[i].name = name;
             device_table[i].ops  = ops;
diff --git a/Source/term_usb.c b/Source/term_usb.c
index b008c3a..c63b893 100644
--- a/Source/term_usb.c
+++ b/Source/term_usb.c
@@ -52,7 +52,7 @@ static uint16_t VCP_DataTx(uint8_t *buf, uint32_t len)
 {
     portBASE_TYPE xHigherPriorityTaskWoken = pdFALSE;
 
-    for (int i=0; i<uxQueueMessagesWaitingFromISR(tx_queue); i++)
+    for (uint32_t i=0; i<uxQueueMessagesWaitingFromISR(tx_queue); i++)
     {
         char c;
         xQueueReceiveFromISR(tx_queue, &c, &xHigherPriorityTaskWoken);
@@ -76,7 +76,7 @@ static uint16_t VCP_DataRx(uint8_t *buf, uint32_t len)
 {
     portBASE_TYPE xHigherPriorityTaskWoken = pdFALSE;
 
-    for (int i=0; i<len; i++) {
+    for (uint32_t i=0; i<len; i++) {
         if (xQueueSendFromISR(rx_queue, &buf[i], &xHigherPriorityTaskWoken))
             usb_stats.rx_bytes++;
         else
@@ -102,7 +102,7 @@ const CDC_IF_Prop_TypeDef VCP_fops = {
 static ssize_t usb_write_r(struct _reent *r, int fd, const void *ptr, size_t len)
 {
     const char *src = ptr;
-    int sent = 0;
+    ssize_t sent = 0;
 
     while (len--) {
         // Convert c-newlines to terminal CRLF
@@ -124,7 +124,7 @@ static ssize_t usb_read_r(struct _reent *r, int fd, void *ptr, size_t len)
     unsigned timeout = portMAX_DELAY;
 
     char *dest = ptr;
-    int  received = 0;
+    ssize_t  received = 0;
     static char last_c;
 
     while (len--) {