basecmd: Move low-level alloc code into basecmd.c

Implement new dynmem_start() and dynmem_end() functions instead of
alloc_chunk() and alloc_chunks() in the board code.  This simplifies
the board code.

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

src/generic/alloc.c

@@ -1,37 +1,23 @@
-// Dummy implementation for alloc commands
+// Generic implementation of dynamic memory pool
 //
 // Copyright (C) 2016,2017  Kevin O'Connor <kevin@koconnor.net>
 //
 // This file may be distributed under the terms of the GNU GPLv3 license.
 
-#include <stdlib.h> // malloc
-#include <string.h> // memset
-#include "command.h" // shutdown
-#include "misc.h" // alloc_chunk
-#include "sched.h" // sched_shutdown
+#include "misc.h" // dynmem_start
 
-// Return the maximum allocation size that can succeed up to 'reqsize'
-size_t
-alloc_chunk_maxsize(size_t reqsize)
-{
-    return reqsize;
-}
+static char dynmem_pool[20 * 1024];
 
-// Allocate an area of memory
+// Return the start of memory available for dynamic allocations
 void *
-alloc_chunk(size_t size)
+dynmem_start(void)
 {
-    void *data = malloc(size);
-    if (!data)
-        shutdown("alloc_chunk failed");
-    memset(data, 0, size);
-    return data;
+    return dynmem_pool;
 }
 
-// Allocate an array of chunks
+// Return the end of memory available for dynamic allocations
 void *
-alloc_chunks(size_t size, size_t count, size_t *avail)
+dynmem_end(void)
 {
-    *avail = count;
-    return alloc_chunk(size * count);
+    return &dynmem_pool[sizeof(dynmem_pool)];
 }