diff --git a/libraries/AP_CANManager/AP_CANManager.cpp b/libraries/AP_CANManager/AP_CANManager.cpp
index 78be64a97c66c..323ba2ed454eb 100644
--- a/libraries/AP_CANManager/AP_CANManager.cpp
+++ b/libraries/AP_CANManager/AP_CANManager.cpp
@@ -149,7 +149,7 @@ void AP_CANManager::init()
         if (hal.can[i] == nullptr) {
             // So if this interface is not allocated allocate it here,
             // also pass the index of the CANBus
-            const_cast <AP_HAL::HAL&> (hal).can[i] = new HAL_CANIface(i);
+            hal.can[i] = new HAL_CANIface(i);
         }
 
         // Initialise the interface we just allocated
@@ -305,7 +305,7 @@ bool AP_CANManager::register_driver(AP_CAN::Protocol dtype, AP_CANDriver *driver
         if (hal.can[i] == nullptr) {
             // if this interface is not allocated allocate it here,
             // also pass the index of the CANBus
-            const_cast <AP_HAL::HAL&> (hal).can[i] = new HAL_CANIface(i);
+            hal.can[i] = new HAL_CANIface(i);
         }
 
         // Initialise the interface we just allocated
diff --git a/libraries/AP_Compass/AP_Compass_AK09916.cpp b/libraries/AP_Compass/AP_Compass_AK09916.cpp
index bb6732365a25d..8630da5e9747b 100644
--- a/libraries/AP_Compass/AP_Compass_AK09916.cpp
+++ b/libraries/AP_Compass/AP_Compass_AK09916.cpp
@@ -58,13 +58,6 @@ extern const AP_HAL::HAL &hal;
 
 extern const AP_HAL::HAL &hal;
 
-struct PACKED sample_regs {
-    uint8_t st1;
-    int16_t val[3];
-    uint8_t tmps;
-    uint8_t st2;
-};
-
 AP_Compass_AK09916::AP_Compass_AK09916(AP_AK09916_BusDriver *bus,
                                         bool force_external,
                                         enum Rotation rotation)
@@ -477,7 +470,7 @@ bool AP_AK09916_BusDriver_Auxiliary::configure()
 
 bool AP_AK09916_BusDriver_Auxiliary::start_measurements()
 {
-    if (_bus->register_periodic_read(_slave, REG_ST1, sizeof(sample_regs)) < 0) {
+    if (_bus->register_periodic_read(_slave, REG_ST1, sizeof(AP_Compass_AK09916::sample_regs)) < 0) {
         return false;
     }
 
diff --git a/libraries/AP_Compass/AP_Compass_AK09916.h b/libraries/AP_Compass/AP_Compass_AK09916.h
index b4cca6e97346e..5c80cff9ef675 100644
--- a/libraries/AP_Compass/AP_Compass_AK09916.h
+++ b/libraries/AP_Compass/AP_Compass_AK09916.h
@@ -75,6 +75,14 @@ class AP_Compass_AK09916 : public AP_Compass_Backend
 
     void read() override;
 
+    /* Must be public so the BusDriver can access its definition */
+    struct PACKED sample_regs {
+        uint8_t st1;
+        int16_t val[3];
+        uint8_t tmps;
+        uint8_t st2;
+    };
+
 private:
     AP_Compass_AK09916(AP_AK09916_BusDriver *bus, bool force_external,
                        enum Rotation rotation);
diff --git a/libraries/AP_Compass/AP_Compass_AK8963.cpp b/libraries/AP_Compass/AP_Compass_AK8963.cpp
index 4c4ced9e3f5c8..ad6a8c6d234ef 100644
--- a/libraries/AP_Compass/AP_Compass_AK8963.cpp
+++ b/libraries/AP_Compass/AP_Compass_AK8963.cpp
@@ -49,11 +49,6 @@
 
 #define AK8963_MILLIGAUSS_SCALE 10.0f
 
-struct PACKED sample_regs {
-    int16_t val[3];
-    uint8_t st2;
-};
-
 extern const AP_HAL::HAL &hal;
 
 AP_Compass_AK8963::AP_Compass_AK8963(AP_AK8963_BusDriver *bus,
@@ -379,7 +374,7 @@ bool AP_AK8963_BusDriver_Auxiliary::configure()
 
 bool AP_AK8963_BusDriver_Auxiliary::start_measurements()
 {
-    if (_bus->register_periodic_read(_slave, AK8963_HXL, sizeof(sample_regs)) < 0) {
+    if (_bus->register_periodic_read(_slave, AK8963_HXL, sizeof(AP_Compass_AK8963::sample_regs)) < 0) {
         return false;
     }
 
diff --git a/libraries/AP_Compass/AP_Compass_AK8963.h b/libraries/AP_Compass/AP_Compass_AK8963.h
index 7b61768d84225..c0f020756571a 100644
--- a/libraries/AP_Compass/AP_Compass_AK8963.h
+++ b/libraries/AP_Compass/AP_Compass_AK8963.h
@@ -39,6 +39,12 @@ class AP_Compass_AK8963 : public AP_Compass_Backend
 
     void read() override;
 
+    /* Must be public so the BusDriver can access its definition */
+    struct PACKED sample_regs {
+        int16_t val[3];
+        uint8_t st2;
+    };
+
 private:
     AP_Compass_AK8963(AP_AK8963_BusDriver *bus,
                       enum Rotation rotation);
diff --git a/libraries/AP_Compass/AP_Compass_LSM9DS1.cpp b/libraries/AP_Compass/AP_Compass_LSM9DS1.cpp
index eeebe00fdca5c..60db0f54de622 100644
--- a/libraries/AP_Compass/AP_Compass_LSM9DS1.cpp
+++ b/libraries/AP_Compass/AP_Compass_LSM9DS1.cpp
@@ -47,11 +47,6 @@
 #define LSM9DS1M_INT_THS_L_M        0x32
 #define LSM9DS1M_INT_THS_H_M        0x33
 
-struct PACKED sample_regs {
-    uint8_t status;
-    int16_t val[3];
-};
-
 extern const AP_HAL::HAL &hal;
 
 AP_Compass_LSM9DS1::AP_Compass_LSM9DS1(AP_HAL::OwnPtr<AP_HAL::Device> dev,
diff --git a/libraries/AP_Compass/AP_Compass_LSM9DS1.h b/libraries/AP_Compass/AP_Compass_LSM9DS1.h
index 2cb91c74c6de4..7017883bd62ad 100644
--- a/libraries/AP_Compass/AP_Compass_LSM9DS1.h
+++ b/libraries/AP_Compass/AP_Compass_LSM9DS1.h
@@ -42,6 +42,11 @@ class AP_Compass_LSM9DS1 : public AP_Compass_Backend
     uint8_t _compass_instance;
     float _scaling;
     enum Rotation _rotation;
+
+    struct PACKED sample_regs {
+        uint8_t status;
+        int16_t val[3];
+    };
 };
 
 #endif
diff --git a/libraries/AP_DroneCAN/examples/DroneCAN_sniffer/DroneCAN_sniffer.cpp b/libraries/AP_DroneCAN/examples/DroneCAN_sniffer/DroneCAN_sniffer.cpp
index 97a7850d41efd..6308046b4215e 100644
--- a/libraries/AP_DroneCAN/examples/DroneCAN_sniffer/DroneCAN_sniffer.cpp
+++ b/libraries/AP_DroneCAN/examples/DroneCAN_sniffer/DroneCAN_sniffer.cpp
@@ -117,7 +117,7 @@ static void cb_GetNodeInfoRequest(const CanardRxTransfer &transfer, const uavcan
 
 void DroneCAN_sniffer::init(void)
 {
-    const_cast <AP_HAL::HAL&> (hal).can[driver_index] = new HAL_CANIface(driver_index);
+    hal.can[driver_index] = new HAL_CANIface(driver_index);
     
     if (hal.can[driver_index] == nullptr) {
         AP_HAL::panic("Couldn't allocate CANManager, something is very wrong");
diff --git a/libraries/AP_HAL/HAL.cpp b/libraries/AP_HAL/HAL.cpp
index a2d1216d2b389..92fa3588e698f 100644
--- a/libraries/AP_HAL/HAL.cpp
+++ b/libraries/AP_HAL/HAL.cpp
@@ -15,7 +15,6 @@ HAL::FunCallbacks::FunCallbacks(void (*setup_fun)(void), void (*loop_fun)(void))
 // access serial ports using SERIALn numbering
 AP_HAL::UARTDriver* AP_HAL::HAL::serial(uint8_t sernum) const
 {
-    UARTDriver **uart_array = const_cast<UARTDriver**>(&uartA);
     // this mapping captures the historical use of uartB as SERIAL3
     const uint8_t mapping[] = { 0, 2, 3, 1, 4, 5, 6, 7, 8, 9 };
     static_assert(sizeof(mapping) == num_serial, "num_serial must match mapping");
diff --git a/libraries/AP_HAL/HAL.h b/libraries/AP_HAL/HAL.h
index f8827444204f4..a3701eb349555 100644
--- a/libraries/AP_HAL/HAL.h
+++ b/libraries/AP_HAL/HAL.h
@@ -53,16 +53,17 @@ class AP_HAL::HAL {
         AP_HAL::CANIface** _can_ifaces)
 #endif
         :
-        uartA(_uartA),
-        uartB(_uartB),
-        uartC(_uartC),
-        uartD(_uartD),
-        uartE(_uartE),
-        uartF(_uartF),
-        uartG(_uartG),
-        uartH(_uartH),
-        uartI(_uartI),
-        uartJ(_uartJ),
+        uart_array{
+            _uartA,
+            _uartB,
+            _uartC,
+            _uartD,
+            _uartE,
+            _uartF,
+            _uartG,
+            _uartH,
+            _uartI,
+            _uartJ},
         i2c_mgr(_i2c_mgr),
         spi(_spi),
         wspi(_wspi),
@@ -112,19 +113,6 @@ class AP_HAL::HAL {
 
     virtual void run(int argc, char * const argv[], Callbacks* callbacks) const = 0;
 
-private:
-    // the uartX ports must be contiguous in ram for the serial() method to work
-    AP_HAL::UARTDriver* uartA;
-    AP_HAL::UARTDriver* uartB UNUSED_PRIVATE_MEMBER;
-    AP_HAL::UARTDriver* uartC UNUSED_PRIVATE_MEMBER;
-    AP_HAL::UARTDriver* uartD UNUSED_PRIVATE_MEMBER;
-    AP_HAL::UARTDriver* uartE UNUSED_PRIVATE_MEMBER;
-    AP_HAL::UARTDriver* uartF UNUSED_PRIVATE_MEMBER;
-    AP_HAL::UARTDriver* uartG UNUSED_PRIVATE_MEMBER;
-    AP_HAL::UARTDriver* uartH UNUSED_PRIVATE_MEMBER;
-    AP_HAL::UARTDriver* uartI UNUSED_PRIVATE_MEMBER;
-    AP_HAL::UARTDriver* uartJ UNUSED_PRIVATE_MEMBER;
-
 public:
     AP_HAL::I2CDeviceManager* i2c_mgr;
     AP_HAL::SPIDeviceManager* spi;
@@ -141,9 +129,9 @@ class AP_HAL::HAL {
     AP_HAL::Flash       *flash;
     AP_HAL::DSP         *dsp;
 #if HAL_NUM_CAN_IFACES > 0
-    AP_HAL::CANIface* can[HAL_NUM_CAN_IFACES];
+    mutable AP_HAL::CANIface* can[HAL_NUM_CAN_IFACES];
 #else
-    AP_HAL::CANIface** can;
+    mutable AP_HAL::CANIface** can;
 #endif
 
     // access to serial ports using SERIALn_ numbering
@@ -151,6 +139,10 @@ class AP_HAL::HAL {
 
     static constexpr uint8_t num_serial = 10;
 
+private:
+    AP_HAL::UARTDriver* uart_array[num_serial];
+
+public:
 #if AP_SIM_ENABLED && CONFIG_HAL_BOARD != HAL_BOARD_SITL
     AP_HAL::SIMState *simstate;
 #endif
diff --git a/libraries/AP_HAL_ChibiOS/CANFDIface.cpp b/libraries/AP_HAL_ChibiOS/CANFDIface.cpp
index 2d261f7242084..0430058d92474 100644
--- a/libraries/AP_HAL_ChibiOS/CANFDIface.cpp
+++ b/libraries/AP_HAL_ChibiOS/CANFDIface.cpp
@@ -85,7 +85,7 @@
 #error "Unsupported MCU for FDCAN"
 #endif
 
-extern AP_HAL::HAL& hal;
+extern const AP_HAL::HAL& hal;
 
 #define STR(x) #x
 #define XSTR(x) STR(x)
diff --git a/libraries/AP_HAL_ChibiOS/CanIface.cpp b/libraries/AP_HAL_ChibiOS/CanIface.cpp
index 677f484804943..49bcfdb47f47d 100644
--- a/libraries/AP_HAL_ChibiOS/CanIface.cpp
+++ b/libraries/AP_HAL_ChibiOS/CanIface.cpp
@@ -84,7 +84,7 @@
 #endif
 
 
-extern AP_HAL::HAL& hal;
+extern const AP_HAL::HAL& hal;
 
 using namespace ChibiOS;