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Consideration about SYS and the first pages of flash ROM
========================================================
About SYS on STM32F103
======================
In the development of Gnuk, we developed:
SYS: The system predefined routines for STM32F103
It is now maintained as example-cdc/sys.c.
There is another version in example-led/sys.c, which also support
STM32F030, as well as STM32F103. But, it wouldn't be useful for
STM32F030. In fact, the file example-fsm-55/sys.c has name sys.c
but it doesn't include any system routines.
Now, I'm developing something like SYS for Kinetis L MCU, so, I write
this document.
The original issue was:
(1) When it's protected, STM32F103 can't change the first 4KiB of
flash ROM at run time.
(2) We want to support firmware upgrade through its USB.
Later on, we add another point.
(3) It is good if the executable of Gnuk could be shared among
different boards.
For (1) and (2), we decided put some useful routines and data which is
not need to be changed.
Now, the first 4KiB of flash ROM consists of:
1KiB: SYS
3KiB: 3/4 of AES forward tables
SYS consists of:
Internal: reset entry, end of RAM
Data: board identification
Routines: board specific
board independent
and here is the list of all.
* Internal routines
reset entry
end of RAM
* Board identification
sys_version
sys_board_id
sys_board_name
* Board specific routines
* led
set_led
* mcu/board lower level
clock_init
gpio_init
* usb
usb_lld_sys_init
usb_lld_sys_shutdown
* Board independent routines
* flash ROM access routines
unlock
write word
erase page
brank check
write page
protect
erase_all & exec to ram
* system reset routine
nvic_system_reset
The routines of clock_init and gpio_init are here because of some
historical reasons. (We could design a system with no such exported
routines: by defining: those things done internally after reset and
before calling the application.)
Those are exported as entries of SYS, and it is the responsibility of
the application which do initialize clock and GPIO, calling those
routines.
USB routines are needed because of hardware practice of STM32F103.
With STM32F103, each board has different way for handling the pull up
of USB D+ and how the device asks re-enumeration to host PC. In my
opinion, if it's defined as full speed device and it's OK for us not
to use high impedance (but asserting to LOW, instead) of D+ to ask
re-enumeration, we can just pull up D+ always. And we wouldn't need
such routines in SYS.
About SYS on Kinetis L
======================
For Kinetis L, because it's ROM has the original firmware upgrade
support by the vendor (though USB HID), all that we needed for
firmware upgrade would be just erasing to factory settings.
--
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