diff --git a/bsp/stm32f40x/readme.txt b/bsp/stm32f40x/readme.txt
new file mode 100644
index 0000000000000000000000000000000000000000..7bebe251c66a8eddbf122610225fdd454a622bce
--- /dev/null
+++ b/bsp/stm32f40x/readme.txt
@@ -0,0 +1,9 @@
+board info:
+STM32F4 discovery
+http://www.st.com/internet/evalboard/product/252419.jsp
+
+note:
+in drivers/stm32f4xx_conf.h
+ /* Redefine the HSE value; it's equal to 8 MHz on the STM32F4-DISCOVERY Kit */
+ #define HSE_VALUE    ((uint32_t)8000000)
+