diff --git a/components/f4ll/.gitignore b/components/f4ll/.gitignore
new file mode 100644
index 0000000..c570f57
--- /dev/null
+++ b/components/f4ll/.gitignore
@@ -0,0 +1,4 @@
+CMakeFiles/
+CMakeCache.txt
+build.ninja
+cmake_install.cmake
\ No newline at end of file
diff --git a/components/f4ll/.gitrepo b/components/f4ll/.gitrepo
index 07c77e9..7046842 100644
--- a/components/f4ll/.gitrepo
+++ b/components/f4ll/.gitrepo
@@ -6,7 +6,7 @@
 [subrepo]
 	remote = ssh://git@codeberg.org/abody/f4ll.git
 	branch = master
-	commit = a4c1baa4109ed591c9db556da430fadfac0642a6
-	parent = 4e1f01c4d45a06b03c631b229402f8c625900922
+	commit = f86c164de5c279c378c5cde408af5fe75497c474
+	parent = d72d3af2a7e99af89780fcfa66071f99db11c766
 	method = merge
 	cmdver = 0.4.9
diff --git a/components/f4ll/CMakeLists.txt b/components/f4ll/CMakeLists.txt
index 0664851..1236174 100644
--- a/components/f4ll/CMakeLists.txt
+++ b/components/f4ll/CMakeLists.txt
@@ -1,3 +1,5 @@
+cmake_minimum_required(VERSION 3.22)
+
 add_library(f4ll STATIC
     src/console_handler.cpp
     src/crc_handler.cpp
@@ -5,6 +7,7 @@ add_library(f4ll STATIC
     src/fault.cpp
     src/memcpy_dma.cpp
     src/packet_usart.cpp
+    src/ringbuffer.cpp
     src/str_util.cpp
     src/usart_core.cpp
 )
diff --git a/components/f4ll/inc/f4ll/console_handler.h b/components/f4ll/inc/f4ll/console_handler.h
index 27a2a7e..210e410 100644
--- a/components/f4ll/inc/f4ll/console_handler.h
+++ b/components/f4ll/inc/f4ll/console_handler.h
@@ -8,8 +8,10 @@
 #pragma once
 
 #include <f4ll/initialized_singleton.h>
-#include <f4ll/packet_usart.h>
 #include <f4ll/ringbuffer.h>
+#include <f4ll/usart_core.h>
+
+#include <platform/dma_ll.h>
 
 namespace f4ll {
 
@@ -18,12 +20,26 @@ class console_handler : public usart_core, public initialized_singleton<console_
     friend class initialized_singleton<console_handler>;
 
 public:
+    using size_type = iringbuffer::size_type;
+
+    class iconsole_input
+    {
+    public:
+        virtual void input_available(size_type len) = 0;
+    };
+
     void print(char const *s);
     void flush();
-    size_t append(char const *s);
+    size_type append(char const *s);
+
+    iringbuffer &get_rx_buffer() { return m_rx_buffer; }
 
 private:
-    console_handler(USART_TypeDef *usart, DMA_TypeDef *dma, uint32_t stream_rx, uint32_t stream_tx);
+    console_handler(
+        USART_TypeDef *usart, DMA_TypeDef *dma, uint32_t stream_rx, uint32_t stream_tx, uint8_t *rx_buffer, size_type x_buffer_size,
+        uint8_t *tx_buffer, size_type tx_buffer_size, iconsole_input *rx_callback);
+
+    void setup_receive(void);
 
     // LL_UsartCore pure virtual function implementations
     virtual void receiver_idle(void) override;
@@ -37,8 +53,13 @@ private:
     virtual void tx_dma_half_transfer(void) override;
     virtual void tx_dma_error(dma_helper::dma_error_type reason) override;
 
-    ringbuffer<128> m_tx_buffer;
-    iringbuffer::size_type m_in_flight_size = 0;
+    ringbuffer_ext m_tx_buffer;
+    size_type m_bytes_sent = 0;
+
+    ringbuffer_ext m_rx_buffer;
+    size_type m_bytes_requested = 0;
+    size_type m_reqd_bytes_registered = 0;
+    iconsole_input *m_rx_callback;
 };
 
 } /* namespace f4ll */
diff --git a/components/f4ll/inc/f4ll/crc_handler.h b/components/f4ll/inc/f4ll/crc_handler.h
index 8fb6b27..26ae056 100644
--- a/components/f4ll/inc/f4ll/crc_handler.h
+++ b/components/f4ll/inc/f4ll/crc_handler.h
@@ -6,10 +6,12 @@
  */
 #pragma once
 
+#include <inttypes.h>
+
+#include <platform/dma_ll.h>
+
 #include <f4ll/dma_helper.h>
 #include <f4ll/initialized_singleton.h>
-#include <inttypes.h>
-#include <platform/dma_ll.h>
 
 namespace f4ll {
 
diff --git a/components/f4ll/inc/f4ll/dma_helper.h b/components/f4ll/inc/f4ll/dma_helper.h
index 82347e7..b2d1045 100644
--- a/components/f4ll/inc/f4ll/dma_helper.h
+++ b/components/f4ll/inc/f4ll/dma_helper.h
@@ -8,6 +8,7 @@
 #pragma once
 
 #include <inttypes.h>
+
 #include <platform/dma_ll.h>
 
 namespace f4ll {
@@ -38,9 +39,9 @@ public:
 
 private:
     DMA_TypeDef *m_dma;
-    uint32_t m_stream;
-    volatile uint32_t *m_is_reg;
-    volatile uint32_t *m_ifc_reg;
+    uint32_t const m_stream;
+    volatile uint32_t * const m_is_reg;
+    volatile uint32_t * const m_ifc_reg;
 
     static constexpr uint32_t const m_fe_masks[8] = {DMA_LISR_FEIF0, DMA_LISR_FEIF1, DMA_LISR_FEIF2, DMA_LISR_FEIF3,
                                                      DMA_HISR_FEIF4, DMA_HISR_FEIF5, DMA_HISR_FEIF6, DMA_HISR_FEIF7};
diff --git a/components/f4ll/inc/f4ll/memcpy_dma.h b/components/f4ll/inc/f4ll/memcpy_dma.h
index 4fcd299..ab728d1 100644
--- a/components/f4ll/inc/f4ll/memcpy_dma.h
+++ b/components/f4ll/inc/f4ll/memcpy_dma.h
@@ -6,6 +6,8 @@
  */
 #pragma once
 
+#include <cstdint>
+
 #include <f4ll/dma_helper.h>
 #include <f4ll/initialized_singleton.h>
 
diff --git a/components/f4ll/inc/f4ll/ringbuffer.h b/components/f4ll/inc/f4ll/ringbuffer.h
index acf39d1..c2dc08d 100644
--- a/components/f4ll/inc/f4ll/ringbuffer.h
+++ b/components/f4ll/inc/f4ll/ringbuffer.h
@@ -9,7 +9,6 @@
 
 #include <cstddef>
 #include <cstdint>
-#include <cstring>
 
 namespace f4ll {
 
@@ -35,22 +34,30 @@ public:
     /// without registering the consumption.
     ///        The caller should also call report_consumption using the returned
     ///        chunk length after it finished processing the data.
-    /// @param[in]  len_requested Length of the data requested from the buffer.
-    /// The length of the actual data provided
-    ///             might be actually smaller (because either reaching the end of
-    ///             the buffer or not enough data in the buffer).
     /// @param[out] data Receives a pointer to the first byte of the available
     /// data in the buffer
     /// @param[out] len Receives the length of the chunk available in the buffer.
     /// Will not exceed len_requested.
     /// @retval true if the buffer has more available data, false otherwise.
-    virtual bool get_chunk(size_type len_requested, uint8_t const *&data, size_type &len) const = 0;
+    virtual bool get_chunk(uint8_t const *&data, size_type &len) const = 0;
 
     /// @brief Marks the chunk returned by ringbuffer_GetChunk as available.
     /// @param consumed The length of the chunk as returned by
     /// ringbuffer_GetChunk(..., len)
     virtual void consumed(size_type len) = 0;
 
+    /// @brief Gets a pointer to the next free chunk in the buffer
+    /// @retval Pointer to the beginning of the next free buffer chmemory area
+    /// @param[out] len Receives the length of the returned buffer area.
+    virtual uint8_t *get_free_chunk(size_type &len) = 0;
+
+    /// @brief Registers the data written in the free buffer chunk.
+    ///        IMPORTANT: Do not call put() after start modifying the buffer
+    ///        returned by get_free_chunk() before registering the written data by
+    ///        calling supplied()
+    /// @param len The length of the data written in the buffer
+    virtual bool produced(size_type len) = 0;
+
     /// @brief Returns the number of uncommited bytes in the ring buffer.
     virtual size_type uncommited() const = 0;
 
@@ -72,15 +79,21 @@ public:
     virtual size_type unused() const = 0;
 };
 
-template <iringbuffer::size_type SZ> class ringbuffer : public iringbuffer
+//
+class ringbuffer_ext : public iringbuffer
 {
 public:
-    ringbuffer() = default;
+    ringbuffer_ext(uint8_t *bptr, size_type bsize);
 
     size_type put(uint8_t const *data, size_type len) override;
     void commit() override;
-    bool get_chunk(size_type len_requested, uint8_t const *&data, size_type &len) const override;
+
+    bool get_chunk(uint8_t const *&data, size_type &len) const override;
     void consumed(size_type len) override;
+
+    uint8_t *get_free_chunk(size_type &len) override;
+    bool produced(size_type len) override;
+
     size_type uncommited() const override;
     size_type commited() const override;
     void discard() override;
@@ -89,130 +102,32 @@ public:
     size_type unused() const override;
 
 private:
-    uint8_t m_buffer[SZ];        //!< Data bufer
+    uint8_t *m_buffer;           //!< Data bufer
+    size_type const m_bsize;     //!< Data buffer size
     size_type m_head = 0;        //!< Write position
     size_type m_head_shadow = 0; //!< Shadowed write position for collecting data
                                  //!< before committing it
     size_type m_tail = 0;        //!< Read position
 
     size_type marker_diff(size_type m1, size_type m2) const;
+    size_type max_chunk_len() const;
 };
 
 //
-template <iringbuffer::size_type SZ> iringbuffer::size_type ringbuffer<SZ>::put(uint8_t const *data, size_type len)
+template <iringbuffer::size_type SZ> class ringbuffer : public ringbuffer_ext
 {
-    size_type chunk1 = 0;
-    size_type chunk2 = 0;
+public:
+    ringbuffer();
 
-    if (!data || !len) {
-        return 0;
-    }
-
-    size_type max_len = unused();
-    len = len < max_len ? len : max_len;
-
-    chunk1 = sizeof(m_buffer) - m_head_shadow;
-    if (chunk1 >= len) {
-        chunk1 = len;
-    } else {
-        chunk2 = len - chunk1;
-    }
-
-    std::memcpy(m_buffer + m_head_shadow, data, chunk1);
-    m_head_shadow += chunk1;
-    if (m_head_shadow == sizeof(m_buffer)) {
-        m_head_shadow = 0;
-    }
-
-    if (chunk2) {
-        std::memcpy(m_buffer, data + chunk1, chunk2);
-        m_head_shadow += chunk2;
-        if (m_head_shadow == sizeof(m_buffer)) {
-            m_head_shadow = 0;
-        }
-    }
-
-    return len;
-}
-
-template <iringbuffer::size_type SZ> void ringbuffer<SZ>::commit()
-{
-    m_head = m_head_shadow;
+private:
+    uint8_t m_buffer[SZ];
 };
 
-template <iringbuffer::size_type SZ> bool ringbuffer<SZ>::get_chunk(size_type len_requested, uint8_t const *&data, size_type &len) const
+//
+template <iringbuffer::size_type SZ>
+ringbuffer<SZ>::ringbuffer()
+    : ringbuffer_ext(m_buffer, SZ)
 {
-    if (!len_requested) {
-        return false;
-    }
-
-    size_type head = m_head;
-    size_type tail = m_tail;
-    size_type chunk_size = head >= tail ? head - tail : sizeof(m_buffer) - tail;
-
-    if (!chunk_size) {
-        len = 0;
-        return false;
-    }
-
-    if (chunk_size > len_requested) {
-        chunk_size = len_requested;
-    }
-    data = m_buffer + tail;
-    len = chunk_size;
-
-    tail += chunk_size;
-    if (tail == sizeof(m_buffer)) {
-        tail = 0;
-    }
-
-    return tail != head;
 }
 
-template <iringbuffer::size_type SZ> void ringbuffer<SZ>::consumed(size_type len)
-{
-    if (!len) {
-        return;
-    }
-    m_tail += len;
-    if (m_tail == sizeof(m_buffer)) {
-        m_tail = 0;
-    }
-}
-
-template <iringbuffer::size_type SZ> iringbuffer::size_type ringbuffer<SZ>::uncommited() const
-{
-    return marker_diff(m_head_shadow, m_head);
-}
-
-template <iringbuffer::size_type SZ> iringbuffer::size_type ringbuffer<SZ>::commited() const
-{
-    return marker_diff(m_head, m_tail);
-}
-
-template <iringbuffer::size_type SZ> void ringbuffer<SZ>::discard()
-{
-    m_head_shadow = m_head;
-}
-
-template <iringbuffer::size_type SZ> iringbuffer::size_type ringbuffer<SZ>::size() const
-{
-    return SZ;
-}
-
-template <iringbuffer::size_type SZ> iringbuffer::size_type ringbuffer<SZ>::used() const
-{
-    return marker_diff(m_head_shadow, m_tail);
-}
-
-template <iringbuffer::size_type SZ> iringbuffer::size_type ringbuffer<SZ>::unused() const
-{
-    return SZ - used() - 1;
-}
-
-template <iringbuffer::size_type SZ> iringbuffer::size_type ringbuffer<SZ>::marker_diff(size_type m1, size_type m2) const
-{
-    return (m1 >= m2) ? (m1 - m2) : (SZ - m2 + m1);
-}
-
-} // namespace f1ll
\ No newline at end of file
+} // namespace f1ll
diff --git a/components/f4ll/inc/f4ll/usart_core.h b/components/f4ll/inc/f4ll/usart_core.h
index 508df34..fa17f2d 100644
--- a/components/f4ll/inc/f4ll/usart_core.h
+++ b/components/f4ll/inc/f4ll/usart_core.h
@@ -31,6 +31,7 @@ protected:
     dma_helper m_tx_dma;
 
 private:
+    // these functions are called from interrup context!
     virtual void receiver_idle(void) = 0;
     virtual void transmission_complete(void) = 0;
     virtual void framing_error(void) = 0;
diff --git a/components/f4ll/src/console_handler.cpp b/components/f4ll/src/console_handler.cpp
index a4ba4a6..e1955f1 100644
--- a/components/f4ll/src/console_handler.cpp
+++ b/components/f4ll/src/console_handler.cpp
@@ -6,31 +6,42 @@
  */
 
 #include <f4ll/console_handler.h>
-#include <f4ll/irq_lock.h>
 #include <f4ll/str_util.h>
 
 #include <cstring>
 
 namespace f4ll {
 
-console_handler::console_handler(USART_TypeDef *usart, DMA_TypeDef *dma, uint32_t stream_rx, uint32_t stream_tx)
-    : usart_core(usart, dma, stream_rx, stream_tx)
+console_handler::console_handler(
+    USART_TypeDef *usart, DMA_TypeDef *dma, uint32_t stream_rx, uint32_t stream_tx, uint8_t *rx_buffer, size_type rx_buffer_size,
+    uint8_t *tx_buffer, size_type tx_buffer_size, iconsole_input *rx_callback)
+    : usart_core(usart, dma, stream_rx, stream_tx),
+      m_tx_buffer(tx_buffer, tx_buffer_size),
+      m_rx_buffer(rx_buffer, rx_buffer_size),
+      m_rx_callback(rx_callback)
 {
+    LL_USART_EnableIT_IDLE(usart);
+    LL_USART_EnableIT_ERROR(usart);
+    setup_receive();
 }
 
-void console_handler::receiver_idle(void) {}
-
-void console_handler::transmission_complete(void)
+void console_handler::setup_receive(void)
 {
-    m_tx_buffer.consumed(m_in_flight_size);
-    if (m_tx_buffer.commited()) {
-        uint8_t const *chunk;
-        m_tx_buffer.get_chunk(m_tx_buffer.size(), chunk, m_in_flight_size);
-        if (m_in_flight_size) {
-            setup_transmit(chunk, m_in_flight_size);
+    uint8_t *bptr = m_rx_buffer.get_free_chunk(m_bytes_requested);
+    m_reqd_bytes_registered = 0;
+    usart_core::setup_receive(bptr, m_bytes_requested);
+}
+
+void console_handler::receiver_idle(void)
+{
+    uint16_t rcvd_bytes = m_bytes_requested - m_reqd_bytes_registered - LL_DMA_GetDataLength(m_rx_dma.get_dma(), m_rx_dma.get_stream());
+    if (rcvd_bytes) {
+    	m_reqd_bytes_registered += rcvd_bytes;
+        m_rx_buffer.produced(rcvd_bytes);
+        m_rx_buffer.commit();
+        if (m_rx_callback) {
+            m_rx_callback->input_available(rcvd_bytes);
         }
-    } else {
-        m_in_flight_size = 0;
     }
 }
 
@@ -38,7 +49,19 @@ void console_handler::framing_error(void) {}
 
 void console_handler::overrun(void) {}
 
-void console_handler::rx_dma_transfer_complete(void) {}
+void console_handler::rx_dma_transfer_complete(void)
+{
+    LL_DMA_DisableStream(m_rx_dma.get_dma(), m_rx_dma.get_stream());
+    uint16_t rcvd_bytes = m_bytes_requested - m_reqd_bytes_registered - LL_DMA_GetDataLength(m_rx_dma.get_dma(), m_rx_dma.get_stream());
+    if (rcvd_bytes) {
+        m_rx_buffer.produced(rcvd_bytes);
+        setup_receive();
+        m_rx_buffer.commit();
+        if (m_rx_callback) {
+            m_rx_callback->input_available(rcvd_bytes);
+        }
+    }
+}
 
 void console_handler::rx_dma_half_transfer(void) {}
 
@@ -53,6 +76,20 @@ void console_handler::tx_dma_transfer_complete(void)
     LL_DMA_DisableStream(m_tx_dma.get_dma(), m_tx_dma.get_stream());
 }
 
+void console_handler::transmission_complete(void)
+{
+    m_tx_buffer.consumed(m_bytes_sent);
+    if (m_tx_buffer.commited()) {
+        uint8_t const *chunk;
+        m_tx_buffer.get_chunk(chunk, m_bytes_sent);
+        if (m_bytes_sent) {
+            setup_transmit(chunk, m_bytes_sent);
+        }
+    } else {
+        m_bytes_sent = 0;
+    }
+}
+
 void console_handler::tx_dma_half_transfer(void) {}
 
 void console_handler::tx_dma_error(dma_helper::dma_error_type reason)
@@ -60,7 +97,7 @@ void console_handler::tx_dma_error(dma_helper::dma_error_type reason)
     (void)reason;
 }
 
-size_t console_handler::append(char const *s)
+console_handler::size_type console_handler::append(char const *s)
 {
     size_t len = strlen(s);
     if (!len) {
@@ -76,14 +113,14 @@ void console_handler::flush()
     }
     m_tx_buffer.commit();
 
-    if (m_in_flight_size) {
+    if (m_bytes_sent) {
         return;
     }
 
     uint8_t const *chunk;
-    m_tx_buffer.get_chunk(m_tx_buffer.size(), chunk, m_in_flight_size);
-    if (m_in_flight_size) {
-        setup_transmit(chunk, m_in_flight_size);
+    m_tx_buffer.get_chunk(chunk, m_bytes_sent);
+    if (m_bytes_sent) {
+        setup_transmit(chunk, m_bytes_sent);
     }
 }
 
diff --git a/components/f4ll/src/fault.cpp b/components/f4ll/src/fault.cpp
index 83ae3c2..d89b280 100644
--- a/components/f4ll/src/fault.cpp
+++ b/components/f4ll/src/fault.cpp
@@ -6,7 +6,7 @@
  *      -c "tpiu config internal <logfile_full_path> uart off <cpufreq>"
  */
 #include <inttypes.h>
-// #include <core_cm4.h>
+
 #include <f4ll/fault.h>
 #include <f4ll/str_util.h>
 #include <stm32f4xx.h>
diff --git a/components/f4ll/src/ringbuffer.cpp b/components/f4ll/src/ringbuffer.cpp
new file mode 100644
index 0000000..ae81ac2
--- /dev/null
+++ b/components/f4ll/src/ringbuffer.cpp
@@ -0,0 +1,152 @@
+#include <f4ll/ringbuffer.h>
+
+#include <cstring>
+
+namespace f4ll {
+
+ringbuffer_ext::ringbuffer_ext(uint8_t *bptr, size_type bsize)
+    : m_buffer(bptr),
+      m_bsize(bsize)
+{
+}
+
+iringbuffer::size_type ringbuffer_ext::put(uint8_t const *data, size_type len)
+{
+    size_type chunk1 = 0;
+    size_type chunk2 = 0;
+
+    if (!data || !len) {
+        return 0;
+    }
+
+    size_type max_len = unused();
+    len = len < max_len ? len : max_len;
+
+    chunk1 = m_bsize - m_head_shadow;
+    if (chunk1 >= len) {
+        chunk1 = len;
+    } else {
+        chunk2 = len - chunk1;
+    }
+
+    std::memcpy(m_buffer + m_head_shadow, data, chunk1);
+    m_head_shadow += chunk1;
+    if (m_head_shadow == m_bsize) {
+        m_head_shadow = 0;
+    }
+
+    if (chunk2) {
+        std::memcpy(m_buffer, data + chunk1, chunk2);
+        m_head_shadow += chunk2;
+        if (m_head_shadow == m_bsize) {
+            m_head_shadow = 0;
+        }
+    }
+
+    return len;
+}
+
+void ringbuffer_ext::commit()
+{
+    m_head = m_head_shadow;
+}
+
+bool ringbuffer_ext::get_chunk(uint8_t const *&data, size_type &len) const
+{
+    size_type head = m_head;
+    size_type tail = m_tail;
+    size_type chunk_size = head >= tail ? head - tail : m_bsize - tail;
+
+    if (!chunk_size) {
+        len = 0;
+        return tail != head;
+    }
+
+    data = m_buffer + tail;
+    len = chunk_size;
+
+    tail += chunk_size;
+    if (tail == m_bsize) {
+        tail = 0;
+    }
+
+    return tail != head;
+}
+
+void ringbuffer_ext::consumed(size_type len)
+{
+    if (!len) {
+        return;
+    }
+    m_tail += len;
+    if (m_tail == m_bsize) {
+        m_tail = 0;
+    }
+}
+
+iringbuffer::size_type ringbuffer_ext::max_chunk_len() const
+{
+    if (m_tail <= m_head_shadow) {
+        return m_bsize - m_head_shadow - (m_tail ? 0 : 1);
+    } else {
+        return m_tail - m_head_shadow - 1;
+    }
+}
+
+uint8_t *ringbuffer_ext::get_free_chunk(size_type &len)
+{
+    len = max_chunk_len();
+
+    return m_buffer + m_head_shadow;
+}
+
+bool ringbuffer_ext::produced(size_type len)
+{
+    size_type max_len = max_chunk_len();
+    if (len > max_len) {
+        return false;
+    }
+    m_head_shadow += len;
+    if (m_head_shadow == m_bsize) {
+        m_head_shadow = 0;
+    }
+    return true;
+}
+
+iringbuffer::size_type ringbuffer_ext::uncommited() const
+{
+    return marker_diff(m_head_shadow, m_head);
+}
+
+iringbuffer::size_type ringbuffer_ext::commited() const
+{
+    return marker_diff(m_head, m_tail);
+}
+
+void ringbuffer_ext::discard()
+{
+    m_head_shadow = m_head;
+}
+
+iringbuffer::size_type ringbuffer_ext::size() const
+{
+    return m_bsize;
+}
+
+iringbuffer::size_type ringbuffer_ext::used() const
+{
+    return marker_diff(m_head_shadow, m_tail);
+}
+
+iringbuffer::size_type ringbuffer_ext::unused() const
+{
+    return m_bsize - used() - 1;
+}
+
+iringbuffer::size_type ringbuffer_ext::marker_diff(size_type m1, size_type m2) const
+{
+    return (m1 >= m2) ? (m1 - m2) : (m_bsize - m2 + m1);
+}
+
+//
+}
diff --git a/components/f4ll/src/str_util.cpp b/components/f4ll/src/str_util.cpp
index 54b95df..9b6ef95 100644
--- a/components/f4ll/src/str_util.cpp
+++ b/components/f4ll/src/str_util.cpp
@@ -1,7 +1,5 @@
 #include <f4ll/str_util.h>
 
-#include <cstdint>
-
 //////////////////////////////////////////////////////////////////////////////
 size_t strcpy_ex(char *dst, char const *src)
 {