megadrive_test1

changeset 3:54739a11be66

find changesets by author, revision, files, or words in the commit message
- .data copy and .bss clearing - also made sure .data and .bss start and end markers are dword-aligned to make sure I can copy 4bytes at a time
author John Tsiombikas <nuclear@member.fsf.org>
date Tue, 31 Jan 2017 07:11:17 +0200
parents 51d1d6761601
children e7138066c7ea
files megadrive.ldscript src/startup.s
diffstat 2 files changed, 25 insertions(+), 3 deletions(-) [+]
line diff
     1.1 --- a/megadrive.ldscript	Mon Jan 30 16:57:51 2017 +0200
     1.2 +++ b/megadrive.ldscript	Tue Jan 31 07:11:17 2017 +0200
     1.3 @@ -21,23 +21,26 @@
     1.4  	.rodata : { * (.rodata); } >rom
     1.5  
     1.6  	/* place the load address of the .data section after .rodata */
     1.7 +	. = ALIGN(4);
     1.8  	_data_lma = .;
     1.9  	_rom_end = _data_lma + _data_size;
    1.10  
    1.11  	/* ---- start of RAM ---- */
    1.12  	. = 0xff0000;
    1.13  	/* place the .data section at the start of RAM */
    1.14 -	.data : AT (_data_lma) {
    1.15 +	.data ALIGN(4): AT (_data_lma) {
    1.16  		_data_start = .;
    1.17  		* (.data);
    1.18 +		. = ALIGN(4);
    1.19  		_data_end = .;
    1.20  	} >ram
    1.21  	_data_size = SIZEOF(.data);
    1.22  
    1.23  	/* place the .bss section at the end */
    1.24 -	.bss : {
    1.25 +	.bss ALIGN(4): {
    1.26  		_bss_start = .;
    1.27  		* (.bss);
    1.28 +		. = ALIGN(4);
    1.29  		_bss_end = .;
    1.30  	} >ram
    1.31  	_bss_size = SIZEOF(.bss);

     2.1 --- a/src/startup.s	Mon Jan 30 16:57:51 2017 +0200
     2.2 +++ b/src/startup.s	Tue Jan 31 07:11:17 2017 +0200
     2.3 @@ -1,8 +1,27 @@
     2.4 -| TODO: copy .data and zero .bss
     2.5  	.text
     2.6  	.extern main
     2.7  
     2.8  	.global start
     2.9  start:
    2.10 +	| copy .data section from ROM to RAM
    2.11 +	move.l #_data_lma, %a0
    2.12 +	move.l #_data_start, %a1
    2.13 +	move.l #_data_end, %a2
    2.14 +	cmp.l %a1, %a2
    2.15 +	beq.s 1f	| skip data copy if the section is empty
    2.16 +0:	move.l (%a0)+, (%a1)+
    2.17 +	cmp.l %a1, %a2
    2.18 +	bne.s 0b
    2.19 +1:
    2.20 +
    2.21 +	| zero the .bss section
    2.22 +	move.l #_bss_start, %a0
    2.23 +	move.l #_bss_end, %a1
    2.24 +	cmp.l %a0, %a1
    2.25 +	beq.s 1f	| skip bss zeroing if the section is empty
    2.26 +0:	clr.l (%a0)+
    2.27 +	cmp.l %a0, %a1
    2.28 +	bne.s 0b
    2.29 +1:
    2.30  	jsr main
    2.31  	stop #0x2700