SHA-256 hash verification of flash slots, pico_hash_binary, flash:: namespace, ring_buffer iterator, non-destructive log

firmware/include/ring_buffer.h

@@ -53,4 +53,15 @@ struct ring_buffer {
         uint16_t len = pending < contig ? pending : contig;
         return {data.data() + offset, len};
     }
+
+    struct iterator {
+        const ring_buffer* rb;
+        uint16_t index;
+        const T& operator*() const { return rb->data[(rb->head + index) % N]; }
+        iterator& operator++() { index++; return *this; }
+        bool operator!=(const iterator& o) const { return index != o.index; }
+    };
+
+    iterator begin() const { return {this, 0}; }
+    iterator end() const { return {this, used()}; }
 };