; ABOUT-SYS
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NIIBE Yutaka
188
mcu/ABOUT-SYS
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188
mcu/ABOUT-SYS
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Consideration about SYS and the first pages of flash ROM
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========================================================
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Now, I'm developing something like SYS for Kinetis L MCU, so, I write
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this document.
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About SYS on STM32F103
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======================
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In the development of Gnuk, we developed:
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SYS: The system predefined routines for STM32F103
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It is now maintained as example-cdc/sys.c.
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There is another version in example-led/sys.c, which also support
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STM32F030, as well as STM32F103. But, it wouldn't be useful for
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STM32F030. In fact, the file example-fsm-55/sys.c has name sys.c
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but it doesn't include any system routines.
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The original issue was:
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(1) When it's protected, STM32F103 can't change the first 4KiB of
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flash ROM at run time.
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(2) We want to support firmware upgrade through its USB.
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Later on, we add another point.
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(3) It is good if the executable of Gnuk could be shared among
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different boards.
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For (1) and (2), we decided put some useful routines and data which is
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not need to be changed.
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Now, the first 4KiB of flash ROM consists of:
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1KiB: SYS
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3KiB: 3/4 of AES forward tables
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SYS consists of:
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Internal: reset entry, end of RAM
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Data: board identification
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Routines: board specific
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board independent
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and here is the list of all.
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* Internal routines
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reset entry
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end of RAM
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* Board identification
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sys_version
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sys_board_id
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sys_board_name
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* Board specific routines
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* led
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set_led
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* mcu/board lower level
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clock_init
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gpio_init
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* usb
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usb_lld_sys_init
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usb_lld_sys_shutdown
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* Board independent routines
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* flash ROM access routines
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unlock
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write halfword
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erase page
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brank check
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write page
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protect
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erase_all & exec to ram
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* system reset routine
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nvic_system_reset
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The routines of clock_init and gpio_init are here because of some
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historical reasons. (We could design a system with no such exported
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routines: by defining: those things done internally after reset and
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before calling the application.)
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Those are exported as entries of SYS, and it is the responsibility of
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the application which do initialize clock and GPIO, calling those
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routines.
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USB routines are needed because of hardware practice of STM32F103.
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With STM32F103, each board has different way for handling the pull up
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of USB D+ and how the device asks re-enumeration to host PC. In my
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opinion, if it's defined as full speed device and it's OK for us not
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to use high impedance (but asserting to LOW, instead) of D+ to ask
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re-enumeration, we can just pull up D+ always. And we wouldn't need
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such routines in SYS.
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About SYS on Kinetis L
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======================
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For Kinetis L, because it's ROM has the original firmware upgrade
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support by the vendor (though USB HID), all that we needed for
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firmware upgrade would be just erasing to factory settings.
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And it has no limitation like STM32F103's first 4KiB flash ROM.
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All pages can be updated at run time.
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Nevertheless, the first two pages (2KiB) of KL27Z is still difficult
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to use.
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So, I decide to introduce something like SYS for Kinetis L.
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* Layout
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Three pages (3KiB) usage:
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------------ The first page
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End of RAM <-- not used but hardware defines this
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Address of reset entry
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sys_version
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sys_board_info (id, name)
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sys_vector
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other SYS routines and data...
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------------ The second page
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FLASH CONFIG: 16-byte
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Reset entry function
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flash routines
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CRC-32 routines
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CRC-32 table (768-byte of CRC-32 table)
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------------ The third page
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MAGIC 256-byte (256-byte of the last part of CRC-32 table)
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...
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vectors (initial MSP, reset, ...)
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...
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* data: Board identification
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sys_version
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sys_board_id
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sys_board_name ; null terminated
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* Board specific routines
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* mcu/board lower level
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clock_init
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gpio_init
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* led
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set_led
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* data: Board independent routines
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* flash ROM access code to be loaded on to RAM
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* system reset routine???
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nvic_system_reset
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* data: vectors for routines and data
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sys_version
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sys_board_id
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address of sys_board_name
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address of set_led
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address of clock_init
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address of gpio_init
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address of ...
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--
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