| Title: | Atari ST, TT, & Falcon |
| Notice: | Please read note 1.0 and its replies before posting! |
| Moderator: | FUNYET::ANDERSON |
| Created: | Mon Apr 04 1988 |
| Last Modified: | Tue May 06 1997 |
| Last Successful Update: | Fri Jun 06 1997 |
| Number of topics: | 1433 |
| Total number of notes: | 10312 |
Does anyone know what order address' are accessed in when you do a long word write with the 68000? For example, if I have two registers like this: ADDRESS NAME ------- ---- 1000 REG1 1002 REG2 and I do a longword write to address 1000, both registers will get written. The question is which register will get written first? I'm guessing that REG1 will get written first, but I can't find any mention of it in my 68000 manuals and I don't have an oscilloscope to check it with. NOTE: This is not a question of what data gets written where, I understand that part. Thanks, Ray
| T.R | Title | User | Personal Name | Date | Lines |
|---|---|---|---|---|---|
| 1317.1 | How would an oscope help? | AIDEV::MISKINIS | Tue Oct 06 1992 20:00 | 6 | |
Hi Ray, I don't have an answer for you... But I'm curious as to how one would use an oscilloscope to find out? _John_ | |||||
| 1317.2 | ASD::MIDIOT::POWERS | Bill Powers ZKO3-2/S11 | Wed Oct 07 1992 09:08 | 13 | |
Ray, I took a look in my 68000 book here, and it doesn't mention the write ordering for moves. I also looked up the movep instruction. So for example suppse I did a movep.l d0,1000H, the byte at 1000h would get written, then the byte at 1002h, then 1004h, then 1006h. The manual explicitly told me that it writes the bytes in ascending order like this. So I would assume that a standard move like you are doing would also write them in ascending order. Thus reg1 would get written first, then reg2. But my manual does not explicitly state this. bill | |||||
| 1317.3 | Test loops, it's been years since I've done this stuff | YNGSTR::WALLACE | Thu Oct 08 1992 13:51 | 42 | |
Thanks for the info Bill.
John, as far as scoping goes, I would hang a probe on each of the two "chip
selects" (ie: uds & rd/-wt & A1) then run a program something like the one
below. What I would expect to see is something like:
Loop n Our wonderfull delay Loop n+1
Probe ----+ +------------------------------------------+ +--------------
on adr |___| |___|
1000
Probe ---------------+ +------------------------------------------+ +---
on adr |___| |___|
1002
1'st 2'nd 1'st 2'nd
Register Register Register Register
to be to be to be to be
written written written written
This particular timing supports the "current theory" that address 1000 is
getting written before addressd 1002.
volatile long *Reg1 = 1000;
main( )
{
while( 1 ) {
/* Add a little delay (not much) so we can tell where the beginning of the
* loop is. You can't do a printf() or anything that would take a long
* time here. If the delay is too long it will a pain/impossible to scope.
*/
nop();
*Reg1 = 0;
}
}
nop( ) {}; /* May have to do something else for good good compilers that
* would optimize this into oblivion.
*/
Ray
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