EASy68K http://www.easy68k.com/EASy68Kforum/ 

MULU & MULS accurate timings http://www.easy68k.com/EASy68Kforum/viewtopic.php?f=9&t=547 
Page 1 of 1 
Author:  da_norf [ Tue Sep 09, 2008 10:16 am ] 
Post subject:  MULU & MULS accurate timings 
It appears to me that the instructions MULU & MULS are always weighted with the number of cycles corresponding to the worst possible case (70 cycles + n cycles for calculating the effective address) in v3.7.11 Beta. According to M68000 User's Manual : Quote: MULS, MULU â€” The multiply algorithm requires 38+2n clocks where n is defined as: MULU: n = the number of ones in the <ea> MULS: n=concatenate the <ea> with a zero as the LSB; n is the resultant number of 10 or 01 patterns in the 17bit source; i.e., worst case happens when the source is $5555. For exemple in v3.7.11 Beta : MULU #160,d1 "costs" 74 cycles whereas in real life it should "cost only" 38+2*2+4=46 cycles if I understand correctly the User's Manual. Will we see these accurate timings in a next version ? 
Author:  profkelly [ Wed Sep 10, 2008 1:03 pm ] 
Post subject:  
From EASy68K Help. "The cycle counter does not take into account pipeline efficiencies. The cycle number displayed tends to be a worst case value and is only intended for relative comparison purposes." 
Author:  profkelly [ Thu Sep 11, 2008 3:20 am ] 
Post subject:  
Sim68Kv3.9.1 will use the aforementioned 38+2n formula to calculate execution times. 
Page 1 of 1  All times are UTC 
Powered by phpBB® Forum Software © phpBB Group http://www.phpbb.com/ 