diff --git a/memory_bus.c b/memory_bus.c
new file mode 100644
index 0000000..304766d
--- /dev/null
+++ b/memory_bus.c
@@ -0,0 +1,104 @@
+/*
+ * This file is part of the flashprog project.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include "flash.h"
+#include "programmer.h"
+
+#include "chipdrivers.h"
+
+static void *programmer_map_flash_region(const struct flashctx *flash, const char *descr,
+					 uintptr_t phys_addr, size_t len)
+{
+	void *ret;
+	if (flash->mst->par.map_flash)
+		ret = flash->mst->par.map_flash(descr, phys_addr, len);
+	else
+		ret = fallback_map(descr, phys_addr, len);
+	msg_gspew("%s: mapping %s from 0x%0*" PRIxPTR " to 0x%0*" PRIxPTR "\n",
+		  __func__, descr, PRIxPTR_WIDTH, phys_addr, PRIxPTR_WIDTH, (uintptr_t) ret);
+	return ret;
+}
+
+static void programmer_unmap_flash_region(const struct flashctx *flash, void *virt_addr, size_t len)
+{
+	if (flash->mst->par.unmap_flash)
+		flash->mst->par.unmap_flash(virt_addr, len);
+	else
+		fallback_unmap(virt_addr, len);
+	msg_gspew("%s: unmapped 0x%0*" PRIxPTR "\n", __func__, PRIxPTR_WIDTH, (uintptr_t)virt_addr);
+}
+
+int prepare_memory_access(struct flashctx *flash, enum preparation_steps prep)
+{
+	/* Init pointers to the fail-safe state to distinguish them later from legit values. */
+	flash->virtual_memory = (chipaddr)ERROR_PTR;
+	flash->virtual_registers = (chipaddr)ERROR_PTR;
+
+	/*
+	 * FIXME: This avoids mapping (and unmapping) of flash chip definitions with size 0.
+	 * These are used for various probing-related hacks that would not map successfully
+	 * anyway and should be removed ASAP.
+	 */
+	if (flash->chip->total_size == 0)
+		return 0;
+
+	const chipsize_t size = flash->chip->total_size * 1024;
+	uintptr_t base = flashbase ? flashbase : (0xffffffff - size + 1);
+	void *addr = programmer_map_flash_region(flash, flash->chip->name, base, size);
+	if (addr == ERROR_PTR) {
+		msg_perr("Could not map flash chip %s at 0x%0*" PRIxPTR ".\n",
+			 flash->chip->name, PRIxPTR_WIDTH, base);
+		return 1;
+	}
+	flash->physical_memory = base;
+	flash->virtual_memory = (chipaddr)addr;
+
+	/*
+	 * FIXME: Special function registers normally live 4 MByte below flash space,
+	 * but it might be somewhere completely different on some chips and programmers,
+	 * or not mappable at all. Ignore these problems for now and always report success.
+	 */
+	if (flash->chip->feature_bits & FEATURE_REGISTERMAP) {
+		base = 0xffffffff - size - 0x400000 + 1;
+		addr = programmer_map_flash_region(flash, "flash chip registers", base, size);
+		if (addr == ERROR_PTR) {
+			msg_pdbg2("Could not map flash chip registers %s at 0x%0*" PRIxPTR ".\n",
+				 flash->chip->name, PRIxPTR_WIDTH, base);
+			return 0;
+		}
+		flash->physical_registers = base;
+		flash->virtual_registers = (chipaddr)addr;
+	}
+	return 0;
+}
+
+void finish_memory_access(struct flashctx *flash)
+{
+	const size_t size = flashprog_flash_getsize(flash);
+
+	if (flash->virtual_registers != (chipaddr)ERROR_PTR) {
+		programmer_unmap_flash_region(flash, (void *)flash->virtual_registers, size);
+		flash->physical_registers = 0;
+		flash->virtual_registers = (chipaddr)ERROR_PTR;
+	}
+
+	if (flash->virtual_memory != (chipaddr)ERROR_PTR) {
+		programmer_unmap_flash_region(flash, (void *)flash->virtual_memory, size);
+		flash->physical_memory = 0;
+		flash->virtual_memory = (chipaddr)ERROR_PTR;
+	}
+}