diff --git a/bsl.c b/bsl.c
index 2768a9f..0b3ceaa 100644
--- a/bsl.c
+++ b/bsl.c
@@ -269,7 +269,7 @@ static int bsl_writemem(device_t dev_base,
 
 		r = bsl_xfer(dev, CMD_RX_DATA, addr, mem, wlen);
 
-		if( r < 0 ) {
+		if (r < 0) {
 			printc_err("bsl: failed to write to 0x%04x\n",
 				addr);
 			return -1;
diff --git a/device.h b/device.h
index fed2b2f..22fca3b 100644
--- a/device.h
+++ b/device.h
@@ -54,6 +54,12 @@ struct device_breakpoint {
 };
 
 struct device {
+	/* Start of code memory. Required to distinguish between flash
+	 * writes (which may require alignment) and RAM writes (which
+	 * don't).
+	 */
+	address_t code_start;
+
 	/* Breakpoint table. This should not be modified directly.
 	 * Instead, you should use the device_setbrk() helper function. This
 	 * will set the appropriate flags and ensure that the breakpoint is
diff --git a/fet.c b/fet.c
index 48f8295..55ebb20 100644
--- a/fet.c
+++ b/fet.c
@@ -43,8 +43,6 @@ struct fet_device {
 	int                             version;
 
 	/* Device-specific information */
-	uint16_t                        code_start;
-
 	uint8_t                         fet_buf[65538];
 	int                             fet_len;
 
@@ -478,7 +476,7 @@ static int xfer(struct fet_device *dev,
 static void show_dev_info(const char *name, const struct fet_device *dev)
 {
 	printc("Device: %s\n", name);
-	printc_dbg("Code memory starts at 0x%04x\n", dev->code_start);
+	printc_dbg("Code memory starts at 0x%04x\n", dev->base.code_start);
 	printc_dbg("Number of breakpoints: %d\n", dev->base.max_breakpoints);
 }
 
@@ -497,7 +495,7 @@ static int identify_old(struct fet_device *dev)
 	memcpy(idtext, dev->fet_reply.data + 4, 32);
 	idtext[32] = 0;
 
-	dev->code_start = LE_WORD(dev->fet_reply.data, 0x24);
+	dev->base.code_start = LE_WORD(dev->fet_reply.data, 0x24);
 	dev->base.max_breakpoints = LE_WORD(dev->fet_reply.data, 0x2a);
 
 	show_dev_info(idtext, dev);
@@ -535,7 +533,7 @@ static int identify_new(struct fet_device *dev, const char *force_id)
 		return -1;
 	}
 
-	dev->code_start = LE_WORD(r->msg29_data, 0);
+	dev->base.code_start = LE_WORD(r->msg29_data, 0);
 	dev->base.max_breakpoints = LE_WORD(r->msg29_data, 0x14);
 
 	show_dev_info(r->name, dev);
@@ -592,7 +590,7 @@ static int do_erase(struct fet_device *dev)
 	}
 
 	if (xfer(dev, C_ERASE, NULL, 0, 3, FET_ERASE_MAIN,
-		 dev->code_start, 0) < 0) {
+		 dev->base.code_start, 0) < 0) {
 		printc_err("fet: erase command failed\n");
 		return -1;
 	}
diff --git a/sim.c b/sim.c
index 5fd00b8..111b534 100644
--- a/sim.c
+++ b/sim.c
@@ -27,6 +27,7 @@
 #include "sim.h"
 
 #define MEM_SIZE	65536
+#define MEM_CODE_START  0x8000
 #define MEM_IO_END      0x200
 
 struct sim_device {
@@ -579,6 +580,7 @@ device_t sim_open(sim_fetch_func_t fetch_func,
 
 	memset(dev, 0, sizeof(*dev));
 
+	dev->base.code_start = MEM_CODE_START;
 	dev->base.max_breakpoints = DEVICE_MAX_BREAKPOINTS;
 	dev->base.destroy = sim_destroy;
 	dev->base.readmem = sim_readmem;