generic: Create generic board infrastructure and move misc.h to it

Instead of creating a misc.h file in each board directory, create a
generic board directory and declare misc.h there.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/avr/misc.c

@@ -0,0 +1,37 @@
+// AVR miscellaneous platform code
+//
+// Copyright (C) 2016  Kevin O'Connor <kevin@koconnor.net>
+//
+// This file may be distributed under the terms of the GNU GPLv3 license.
+
+#include <avr/io.h> // AVR_STACK_POINTER_REG
+#include <stdlib.h> // __malloc_heap_end
+#include <util/crc16.h> // _crc_ccitt_update
+#include "autoconf.h" // CONFIG_AVR_STACK_SIZE
+#include "board/misc.h" // alloc_maxsize
+#include "compiler.h" // ALIGN
+
+// Optimized crc16_ccitt for the avr processor
+uint16_t
+crc16_ccitt(char *buf, uint8_t len)
+{
+    uint16_t crc = 0xFFFF;
+    while (len--)
+        crc = _crc_ccitt_update(crc, *buf++);
+    return crc;
+}
+
+// Return the maximum allocation size that can succeed up to 'reqsize'
+size_t
+alloc_maxsize(size_t reqsize)
+{
+    uint16_t memend = ALIGN(AVR_STACK_POINTER_REG, 256);
+    __malloc_heap_end = (void*)memend - CONFIG_AVR_STACK_SIZE;
+    extern char *__brkval;
+    int16_t maxsize = __malloc_heap_end - __brkval - 2;
+    if (maxsize < 0)
+        return 0;
+    if (reqsize < maxsize)
+        return reqsize;
+    return maxsize;
+}