SRAM backup: documentation, config for offset+size

.global asm_load_all

.global asm_load_mem

stack_backup:

    .space 2048

#define SRAM_BASE #1c00h

#define SRAM_SIZE 2048

; SRAM backup space

sram_backup:

    .space SRAM_SIZE

; Stack Pointer backup

sp_backup:

    .space 2

; Backup Cookie: Do we have valid data or has the FRAM been wiped?

backup_cookie:

    .space 2

; save entire SRAM and CPU register state to persistent FRAM

asm_save_all:

    dint

    ; r4 to r11 are callee saved -> push them to the stack.

    ; As we will save the entire SRAM (including stack), they are

    ; included in the SRAM backup and can be popped when restoring it.

    .irp reg,4,5,6,7,8,9,10,11

    push r\reg

    .endr

    ; We will soon have valid data

    mov #1234h, r10

    mov r10, &backup_cookie

    mov r1, &sp_backup

    mov #1c00h, r10

    mov #stack_backup, r11

    mov SRAM_BASE, r10

    mov #sram_backup, r11

    ; Interrupts may alter global variables in SRAM and thus lead to inconsistencies

    dint

save_sram_word:

    mov @r10+, 0(r11)

    add #2, r11

    cmp #1c00h+2048, r10

    cmp SRAM_BASE+SRAM_SIZE, r10

    jlo save_sram_word

    eint

    ; revert changes to callee-saved registers

    pop r11

    pop r10

    ; remove unchanged registers from stack

    add #12, r1

    eint

    ret

; load entire SRAM and CPU register stat from persistent FRAM,

; if it contains valid backup data. Execution will resume at the

; last place where asm_save_all() was called is if nothing in between

; had happened. Does not take possible the state of hardware peripherals

; into account.

asm_load_all:

    dint

    ; check if we have backup data

    push r11

    mov &backup_cookie, r11

    cmp #1234h, r11

    ; yes? -> load it

    jeq do_load_all

    ; no? -> too bad, resume with normal startup

    pop r11

    eint

    ret

do_load_all:

    ; restore SRAM from backup

    mov #stack_backup, r10

    mov #1c00h, r11

    mov #sram_backup, r10

    mov SRAM_BASE, r11

    dint

load_sram_word:

    mov @r10+, 0(r11)

    add #2, r11

    cmp #1c00h+2048, r11

    cmp SRAM_BASE+SRAM_SIZE, r11

    jlo load_sram_word

    ; restore stack pointer

    ; -> execution will continue where asm_save_all was called

    ret

; Load global objects from persistent FRAM, if it contains valid backup data.

; Stack and CPU registers are left as-is, the program flow is not altered.

asm_load_mem:

    dint

    push r11

    mov &backup_cookie, r11

do_load_mem:

    push r10

    push r9

    ; restore SRAM from backup, excluding current stack frame

    ; restore SRAM from backup, excluding stack

    ; -> everything from SRAM start (inclusive) to @sp (exclusive). Reminder: SP == R1 on MSP430

    mov r1, r9

    sub 6, r9

    mov #stack_backup, r10

    mov #1c00h, r11

    mov #sram_backup, r10

    mov SRAM_BASE, r11

    dint

load_sram_word2:

    mov @r10+, 0(r11)

    add #2, r11