diff --git a/Chapter07/error_handling/cstdlib_support/retarget.cpp b/Chapter07/error_handling/cstdlib_support/retarget.cpp
index 60db0bf..f2dd14c 100644
--- a/Chapter07/error_handling/cstdlib_support/retarget.cpp
+++ b/Chapter07/error_handling/cstdlib_support/retarget.cpp
@@ -4,6 +4,8 @@
 #include <stdio.h>
 #include <sys/stat.h>
 
+#include <span>
+
 namespace 
 {
 hal::uart *uart_stdio;
@@ -26,7 +28,7 @@ extern "C" int _write(int fd, char * ptr, int len)
 {
     if(fd == STDOUT_FILENO || fd == STDERR_FILENO)
     {
-        uart_stdio->write_array(ptr, len);
+        uart_stdio->write(std::span<const char>(ptr, len));
     }
 
     return len;
diff --git a/Chapter07/error_handling/hal/uart/inc/uart.hpp b/Chapter07/error_handling/hal/uart/inc/uart.hpp
index 534c3df..a7145dd 100644
--- a/Chapter07/error_handling/hal/uart/inc/uart.hpp
+++ b/Chapter07/error_handling/hal/uart/inc/uart.hpp
@@ -10,11 +10,6 @@ class uart
 {
   public:
     virtual void init(std::uint32_t baudrate) = 0;
-    virtual void write_array(const char * ptr, std::size_t len) = 0;
-
-    virtual void write(std::span<const char> data)
-    {
-      write_array(data.data(), data.size());
-    }
+    virtual void write(std::span<const char> data) = 0;
 };
 }; // namespace hal
diff --git a/Chapter07/error_handling/hal/uart/inc/uart_stm32.hpp b/Chapter07/error_handling/hal/uart/inc/uart_stm32.hpp
index 0653582..f30c529 100644
--- a/Chapter07/error_handling/hal/uart/inc/uart_stm32.hpp
+++ b/Chapter07/error_handling/hal/uart/inc/uart_stm32.hpp
@@ -18,7 +18,7 @@ class uart_stm32 : public uart
 
     void init(std::uint32_t baudrate = c_baudrate_default) override;
 
-    void write_array(const char * ptr, std::size_t len) override;
+    void write(std::span<const char> data) override;
 
   private:
     UART_HandleTypeDef huart_;
diff --git a/Chapter07/error_handling/hal/uart/src/uart_stm32.cpp b/Chapter07/error_handling/hal/uart/src/uart_stm32.cpp
index 59633c6..50b0c7a 100644
--- a/Chapter07/error_handling/hal/uart/src/uart_stm32.cpp
+++ b/Chapter07/error_handling/hal/uart/src/uart_stm32.cpp
@@ -22,10 +22,10 @@ void hal::uart_stm32::init(std::uint32_t baudrate)
     HAL_UART_Init(&huart_);
 }
 
-void hal::uart_stm32::write_array(const char * ptr, std::size_t len)
+void hal::uart_stm32::write(std::span<const char> data) 
 {
     // we must cast away costness due to ST HAL's API
-    char * data_ptr = const_cast<char *>(ptr);
-    HAL_UART_Transmit(&huart_, reinterpret_cast<uint8_t *>(data_ptr), len,
+    char * data_ptr = const_cast<char *>(data.data());
+    HAL_UART_Transmit(&huart_, reinterpret_cast<uint8_t *>(data_ptr), data.size(),
                       HAL_MAX_DELAY);
 }
\ No newline at end of file
diff --git a/Chapter09/type_safety/CMakeLists.txt b/Chapter09/type_safety/CMakeLists.txt
index 1b10db1..f133d89 100644
--- a/Chapter09/type_safety/CMakeLists.txt
+++ b/Chapter09/type_safety/CMakeLists.txt
@@ -11,7 +11,7 @@ set(CMAKE_SIZE "arm-none-eabi-size")
 set(RENODE "renode" CACHE STRING "Path to Renode executable")
 
 set(MAIN_CPP_PATH "${CMAKE_SOURCE_DIR}/app/src/")
-set(MAIN_CPP_FILE_NAME "main_integer_promotion.cpp" CACHE STRING "main file")
+set(MAIN_CPP_FILE_NAME "main_usual_arithmetic_conversion.cpp" CACHE STRING "main file")
 list(APPEND LIB_SPECS "-specs=nosys.specs")
 list(APPEND LIB_SPECS "-specs=nano.specs")
 
diff --git a/Chapter09/type_safety/cstdlib_support/retarget.cpp b/Chapter09/type_safety/cstdlib_support/retarget.cpp
index 60db0bf..f2dd14c 100644
--- a/Chapter09/type_safety/cstdlib_support/retarget.cpp
+++ b/Chapter09/type_safety/cstdlib_support/retarget.cpp
@@ -4,6 +4,8 @@
 #include <stdio.h>
 #include <sys/stat.h>
 
+#include <span>
+
 namespace 
 {
 hal::uart *uart_stdio;
@@ -26,7 +28,7 @@ extern "C" int _write(int fd, char * ptr, int len)
 {
     if(fd == STDOUT_FILENO || fd == STDERR_FILENO)
     {
-        uart_stdio->write_array(ptr, len);
+        uart_stdio->write(std::span<const char>(ptr, len));
     }
 
     return len;
diff --git a/Chapter09/type_safety/hal/uart/inc/uart.hpp b/Chapter09/type_safety/hal/uart/inc/uart.hpp
index 534c3df..a7145dd 100644
--- a/Chapter09/type_safety/hal/uart/inc/uart.hpp
+++ b/Chapter09/type_safety/hal/uart/inc/uart.hpp
@@ -10,11 +10,6 @@ class uart
 {
   public:
     virtual void init(std::uint32_t baudrate) = 0;
-    virtual void write_array(const char * ptr, std::size_t len) = 0;
-
-    virtual void write(std::span<const char> data)
-    {
-      write_array(data.data(), data.size());
-    }
+    virtual void write(std::span<const char> data) = 0;
 };
 }; // namespace hal
diff --git a/Chapter09/type_safety/hal/uart/inc/uart_stm32.hpp b/Chapter09/type_safety/hal/uart/inc/uart_stm32.hpp
index 0653582..f30c529 100644
--- a/Chapter09/type_safety/hal/uart/inc/uart_stm32.hpp
+++ b/Chapter09/type_safety/hal/uart/inc/uart_stm32.hpp
@@ -18,7 +18,7 @@ class uart_stm32 : public uart
 
     void init(std::uint32_t baudrate = c_baudrate_default) override;
 
-    void write_array(const char * ptr, std::size_t len) override;
+    void write(std::span<const char> data) override;
 
   private:
     UART_HandleTypeDef huart_;
diff --git a/Chapter09/type_safety/hal/uart/src/uart_stm32.cpp b/Chapter09/type_safety/hal/uart/src/uart_stm32.cpp
index 59633c6..50b0c7a 100644
--- a/Chapter09/type_safety/hal/uart/src/uart_stm32.cpp
+++ b/Chapter09/type_safety/hal/uart/src/uart_stm32.cpp
@@ -22,10 +22,10 @@ void hal::uart_stm32::init(std::uint32_t baudrate)
     HAL_UART_Init(&huart_);
 }
 
-void hal::uart_stm32::write_array(const char * ptr, std::size_t len)
+void hal::uart_stm32::write(std::span<const char> data) 
 {
     // we must cast away costness due to ST HAL's API
-    char * data_ptr = const_cast<char *>(ptr);
-    HAL_UART_Transmit(&huart_, reinterpret_cast<uint8_t *>(data_ptr), len,
+    char * data_ptr = const_cast<char *>(data.data());
+    HAL_UART_Transmit(&huart_, reinterpret_cast<uint8_t *>(data_ptr), data.size(),
                       HAL_MAX_DELAY);
 }
\ No newline at end of file
diff --git a/Chapter10/lambdas/cstdlib_support/retarget.cpp b/Chapter10/lambdas/cstdlib_support/retarget.cpp
index 60db0bf..f2dd14c 100644
--- a/Chapter10/lambdas/cstdlib_support/retarget.cpp
+++ b/Chapter10/lambdas/cstdlib_support/retarget.cpp
@@ -4,6 +4,8 @@
 #include <stdio.h>
 #include <sys/stat.h>
 
+#include <span>
+
 namespace 
 {
 hal::uart *uart_stdio;
@@ -26,7 +28,7 @@ extern "C" int _write(int fd, char * ptr, int len)
 {
     if(fd == STDOUT_FILENO || fd == STDERR_FILENO)
     {
-        uart_stdio->write_array(ptr, len);
+        uart_stdio->write(std::span<const char>(ptr, len));
     }
 
     return len;
diff --git a/Chapter10/lambdas/hal/uart/inc/uart.hpp b/Chapter10/lambdas/hal/uart/inc/uart.hpp
index 534c3df..a7145dd 100644
--- a/Chapter10/lambdas/hal/uart/inc/uart.hpp
+++ b/Chapter10/lambdas/hal/uart/inc/uart.hpp
@@ -10,11 +10,6 @@ class uart
 {
   public:
     virtual void init(std::uint32_t baudrate) = 0;
-    virtual void write_array(const char * ptr, std::size_t len) = 0;
-
-    virtual void write(std::span<const char> data)
-    {
-      write_array(data.data(), data.size());
-    }
+    virtual void write(std::span<const char> data) = 0;
 };
 }; // namespace hal
diff --git a/Chapter10/lambdas/hal/uart/inc/uart_stm32.hpp b/Chapter10/lambdas/hal/uart/inc/uart_stm32.hpp
index 0653582..f30c529 100644
--- a/Chapter10/lambdas/hal/uart/inc/uart_stm32.hpp
+++ b/Chapter10/lambdas/hal/uart/inc/uart_stm32.hpp
@@ -18,7 +18,7 @@ class uart_stm32 : public uart
 
     void init(std::uint32_t baudrate = c_baudrate_default) override;
 
-    void write_array(const char * ptr, std::size_t len) override;
+    void write(std::span<const char> data) override;
 
   private:
     UART_HandleTypeDef huart_;
diff --git a/Chapter10/lambdas/hal/uart/src/uart_stm32.cpp b/Chapter10/lambdas/hal/uart/src/uart_stm32.cpp
index 59633c6..50b0c7a 100644
--- a/Chapter10/lambdas/hal/uart/src/uart_stm32.cpp
+++ b/Chapter10/lambdas/hal/uart/src/uart_stm32.cpp
@@ -22,10 +22,10 @@ void hal::uart_stm32::init(std::uint32_t baudrate)
     HAL_UART_Init(&huart_);
 }
 
-void hal::uart_stm32::write_array(const char * ptr, std::size_t len)
+void hal::uart_stm32::write(std::span<const char> data) 
 {
     // we must cast away costness due to ST HAL's API
-    char * data_ptr = const_cast<char *>(ptr);
-    HAL_UART_Transmit(&huart_, reinterpret_cast<uint8_t *>(data_ptr), len,
+    char * data_ptr = const_cast<char *>(data.data());
+    HAL_UART_Transmit(&huart_, reinterpret_cast<uint8_t *>(data_ptr), data.size(),
                       HAL_MAX_DELAY);
 }
\ No newline at end of file
diff --git a/Chapter11/compile_time/cstdlib_support/retarget.cpp b/Chapter11/compile_time/cstdlib_support/retarget.cpp
index 60db0bf..f2dd14c 100644
--- a/Chapter11/compile_time/cstdlib_support/retarget.cpp
+++ b/Chapter11/compile_time/cstdlib_support/retarget.cpp
@@ -4,6 +4,8 @@
 #include <stdio.h>
 #include <sys/stat.h>
 
+#include <span>
+
 namespace 
 {
 hal::uart *uart_stdio;
@@ -26,7 +28,7 @@ extern "C" int _write(int fd, char * ptr, int len)
 {
     if(fd == STDOUT_FILENO || fd == STDERR_FILENO)
     {
-        uart_stdio->write_array(ptr, len);
+        uart_stdio->write(std::span<const char>(ptr, len));
     }
 
     return len;
diff --git a/Chapter11/compile_time/hal/uart/inc/uart.hpp b/Chapter11/compile_time/hal/uart/inc/uart.hpp
index 534c3df..a7145dd 100644
--- a/Chapter11/compile_time/hal/uart/inc/uart.hpp
+++ b/Chapter11/compile_time/hal/uart/inc/uart.hpp
@@ -10,11 +10,6 @@ class uart
 {
   public:
     virtual void init(std::uint32_t baudrate) = 0;
-    virtual void write_array(const char * ptr, std::size_t len) = 0;
-
-    virtual void write(std::span<const char> data)
-    {
-      write_array(data.data(), data.size());
-    }
+    virtual void write(std::span<const char> data) = 0;
 };
 }; // namespace hal
diff --git a/Chapter11/compile_time/hal/uart/inc/uart_stm32.hpp b/Chapter11/compile_time/hal/uart/inc/uart_stm32.hpp
index 0653582..f30c529 100644
--- a/Chapter11/compile_time/hal/uart/inc/uart_stm32.hpp
+++ b/Chapter11/compile_time/hal/uart/inc/uart_stm32.hpp
@@ -18,7 +18,7 @@ class uart_stm32 : public uart
 
     void init(std::uint32_t baudrate = c_baudrate_default) override;
 
-    void write_array(const char * ptr, std::size_t len) override;
+    void write(std::span<const char> data) override;
 
   private:
     UART_HandleTypeDef huart_;
diff --git a/Chapter11/compile_time/hal/uart/src/uart_stm32.cpp b/Chapter11/compile_time/hal/uart/src/uart_stm32.cpp
index 59633c6..50b0c7a 100644
--- a/Chapter11/compile_time/hal/uart/src/uart_stm32.cpp
+++ b/Chapter11/compile_time/hal/uart/src/uart_stm32.cpp
@@ -22,10 +22,10 @@ void hal::uart_stm32::init(std::uint32_t baudrate)
     HAL_UART_Init(&huart_);
 }
 
-void hal::uart_stm32::write_array(const char * ptr, std::size_t len)
+void hal::uart_stm32::write(std::span<const char> data) 
 {
     // we must cast away costness due to ST HAL's API
-    char * data_ptr = const_cast<char *>(ptr);
-    HAL_UART_Transmit(&huart_, reinterpret_cast<uint8_t *>(data_ptr), len,
+    char * data_ptr = const_cast<char *>(data.data());
+    HAL_UART_Transmit(&huart_, reinterpret_cast<uint8_t *>(data_ptr), data.size(),
                       HAL_MAX_DELAY);
 }
\ No newline at end of file
diff --git a/Chapter12/cpp_hal/app/src/main_basic_reg.cpp b/Chapter12/cpp_hal/app/src/main_basic_reg.cpp
index aac2808..95be8e7 100644
--- a/Chapter12/cpp_hal/app/src/main_basic_reg.cpp
+++ b/Chapter12/cpp_hal/app/src/main_basic_reg.cpp
@@ -51,8 +51,6 @@ int main()
 
     // RCC->CR = 0xDEADBEEF;
     rcc::write(0xDEADBEEF);
-    auto val = rcc::read();
-    printf("val = %ld\r\n", val);
 
     print_reg(&(RCC->CR));
     
diff --git a/Chapter12/cpp_hal/cstdlib_support/retarget.cpp b/Chapter12/cpp_hal/cstdlib_support/retarget.cpp
index 60db0bf..f2dd14c 100644
--- a/Chapter12/cpp_hal/cstdlib_support/retarget.cpp
+++ b/Chapter12/cpp_hal/cstdlib_support/retarget.cpp
@@ -4,6 +4,8 @@
 #include <stdio.h>
 #include <sys/stat.h>
 
+#include <span>
+
 namespace 
 {
 hal::uart *uart_stdio;
@@ -26,7 +28,7 @@ extern "C" int _write(int fd, char * ptr, int len)
 {
     if(fd == STDOUT_FILENO || fd == STDERR_FILENO)
     {
-        uart_stdio->write_array(ptr, len);
+        uart_stdio->write(std::span<const char>(ptr, len));
     }
 
     return len;
diff --git a/Chapter12/cpp_hal/hal/uart/inc/uart.hpp b/Chapter12/cpp_hal/hal/uart/inc/uart.hpp
index 534c3df..a7145dd 100644
--- a/Chapter12/cpp_hal/hal/uart/inc/uart.hpp
+++ b/Chapter12/cpp_hal/hal/uart/inc/uart.hpp
@@ -10,11 +10,6 @@ class uart
 {
   public:
     virtual void init(std::uint32_t baudrate) = 0;
-    virtual void write_array(const char * ptr, std::size_t len) = 0;
-
-    virtual void write(std::span<const char> data)
-    {
-      write_array(data.data(), data.size());
-    }
+    virtual void write(std::span<const char> data) = 0;
 };
 }; // namespace hal
diff --git a/Chapter12/cpp_hal/hal/uart/inc/uart_stm32.hpp b/Chapter12/cpp_hal/hal/uart/inc/uart_stm32.hpp
index 0653582..f30c529 100644
--- a/Chapter12/cpp_hal/hal/uart/inc/uart_stm32.hpp
+++ b/Chapter12/cpp_hal/hal/uart/inc/uart_stm32.hpp
@@ -18,7 +18,7 @@ class uart_stm32 : public uart
 
     void init(std::uint32_t baudrate = c_baudrate_default) override;
 
-    void write_array(const char * ptr, std::size_t len) override;
+    void write(std::span<const char> data) override;
 
   private:
     UART_HandleTypeDef huart_;
diff --git a/Chapter12/cpp_hal/hal/uart/src/uart_stm32.cpp b/Chapter12/cpp_hal/hal/uart/src/uart_stm32.cpp
index 59633c6..50b0c7a 100644
--- a/Chapter12/cpp_hal/hal/uart/src/uart_stm32.cpp
+++ b/Chapter12/cpp_hal/hal/uart/src/uart_stm32.cpp
@@ -22,10 +22,10 @@ void hal::uart_stm32::init(std::uint32_t baudrate)
     HAL_UART_Init(&huart_);
 }
 
-void hal::uart_stm32::write_array(const char * ptr, std::size_t len)
+void hal::uart_stm32::write(std::span<const char> data) 
 {
     // we must cast away costness due to ST HAL's API
-    char * data_ptr = const_cast<char *>(ptr);
-    HAL_UART_Transmit(&huart_, reinterpret_cast<uint8_t *>(data_ptr), len,
+    char * data_ptr = const_cast<char *>(data.data());
+    HAL_UART_Transmit(&huart_, reinterpret_cast<uint8_t *>(data_ptr), data.size(),
                       HAL_MAX_DELAY);
 }
\ No newline at end of file