List all protocols in "protocol.txt"

Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>

Author: borneoa

protocol.txt

@@ -1,5 +1,19 @@
+The communication protocol used by ST bootloader is documented in following ST
+application notes, depending on communication port.
 
-The protocol used by the STM32 serial bootloader is described in the 
-AN3155 application note "USART protocol used in the STM32 bootloader"
-from STMicroelectronics, available at http://www.st.com/ (search for AN3155).
+In current version of stm32flash are supported only UART and I2C ports.
 
+* AN3154: CAN protocol used in the STM32 bootloader
+  http://www.st.com/web/en/resource/technical/document/application_note/CD00264321.pdf
+
+* AN3155: USART protocol used in the STM32(TM) bootloader
+  http://www.st.com/web/en/resource/technical/document/application_note/CD00264342.pdf
+
+* AN4221: I2C protocol used in the STM32 bootloader
+  http://www.st.com/web/en/resource/technical/document/application_note/DM00072315.pdf
+
+* AN4286: SPI protocol used in the STM32 bootloader
+  http://www.st.com/web/en/resource/technical/document/application_note/DM00081379.pdf
+
+Boot mode selection for STM32 is documented in ST application note AN2606, available in ST website:
+  http://www.st.com/web/en/resource/technical/document/application_note/CD00167594.pdf