diff --git a/src/northbridge/intel/i440bx/ram_calc.c b/src/northbridge/intel/i440bx/ram_calc.c
new file mode 100644
index 0000000..c9bfc2d
--- /dev/null
+++ b/src/northbridge/intel/i440bx/ram_calc.c
@@ -0,0 +1,64 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * Copyright (C) 2017 Keith Hui <buurin@gmail.com>
+ *
+ * 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; version 2 of the License.
+ *
+ * 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.
+ */
+
+#define __SIMPLE_DEVICE__
+
+#include <arch/io.h>
+#include <cbmem.h>
+#include <commonlib/helpers.h>
+#include "i440bx.h"
+
+void *cbmem_top(void)
+{
+	/* Base of TSEG is top of usable DRAM */
+	/*
+	 * SMRAM - System Management RAM Control Register
+	 * 0x72
+	 * [7:4] Not relevant to this function.
+	 * [3:3] Global SMRAM Enable (G_SMRAME)
+	 * [2:0] Hardwired to 010.
+	 *
+	 * ESMRAMC - Extended System Management RAM Control
+	 * 0x73
+	 * [7:7] H_SMRAM_EN
+	 *       1 = When G_SMRAME=1, High SMRAM space is enabled at
+	 *           0x100A0000-0x100FFFFF and forwarded to DRAM address
+	 *           0x000A0000-0x000FFFFF.
+	 *       0 = When G_SMRAME=1, Compatible SMRAM space is enabled at
+	 *           0x000A0000-0x000BFFFF.
+	 * [6:3] Not relevant to this function.
+	 * [2:1] TSEG Size (T_SZ)
+	 *       Selects the size of the TSEG memory block, if enabled.
+	 *       00 = 128KiB
+	 *       01 = 256KiB
+	 *       10 = 512KiB
+	 *       11 = 1MiB
+	 * [0:0] TSEG_EN
+	 *       When SMRAM[G_SMRAME] and this bit are 1, TSEG is enabled to
+	 *       appear between DRAM address (TOM-<TSEG Size>) to TOM.
+	 *
+	 * Source: 440BX datasheet, pages 3-28 thru 3-29.
+	 */
+	unsigned long tom = pci_read_config8(NB, DRB7) * 8 * MiB;
+
+	int gsmrame = pci_read_config8(NB, SMRAM) & 0x8;
+	/* T_SZ and TSEG_EN */
+	int tseg = pci_read_config8(NB, ESMRAMC) & 0x7;
+	if ((tseg & 0x1) && gsmrame) {
+		int tseg_size = 128 * KiB * (1 << (tseg >> 1));
+		tom -= tseg_size;
+	}
+	return (void *)tom;
+}