diff --git a/atusb/fw/flash.c b/atusb/fw/flash.c
index cd29b5b..3b12a56 100644
--- a/atusb/fw/flash.c
+++ b/atusb/fw/flash.c
@@ -14,6 +14,7 @@
 #include <stdint.h>
 
 #include <avr/boot.h>
+#include <avr/pgmspace.h>
 
 #include "dfu.h"
 #include "board.h"
@@ -30,7 +31,7 @@ void flash_start(void)
 
 int flash_can_write(uint16_t size)
 {
-	return 1;
+	return payload+size <= BOOT_ADDR;
 }
 
 
@@ -67,5 +68,13 @@ void flash_write(const uint8_t *buf, uint16_t size)
 
 uint16_t flash_read(uint8_t *buf, uint16_t size)
 {
-	return 0;
+	uint16_t got = 0;
+
+	while (size && payload != (uint32_t) FLASHEND+1) {
+		*buf++ = pgm_read_byte(payload);
+		payload++;
+		size--;
+		got++;
+	}
+	return got;
 }