imp@crayview.msi.umn.edu (Chuck Lukaszewski) (12/31/88)
The .Sony and .Sound drivers, which are located in ROM (i.e. above $400000) both install VBLs during the course of their operation. I have looked at the code for both and neither relocates the VBL task. Rather, the actual address of the routine is put into the Vertical Retrace Queue element. I am loathe to believe that the VBL Task Handler has a special test that permits VBLs below BufPtr and above ROMBase. Not only does it seem pointless to create a VBL desert anywhere in memory, but also the instruction waste would be ludicrous, even for Apple :-). So it seems safe to say that VBLs are safe above BufPtr. Anyone from Apple care to comment? It also occurs to me that I have seen _VInstall and _VRemove in the .MPP or .ATP driver, which are also in ROM. ______________________________________________________________________________ Chuck Lukaszewski imp@crayview.msi.umn.edu 612 789 0931
tim@hoptoad.uucp (Tim Maroney) (01/02/89)
In article <10606@umn-cs.CS.UMN.EDU> imp@crayview.msi.umn.edu (Chuck Lukaszewski) writes: >I am loathe to believe that the VBL Task Handler has a special test that >permits VBLs below BufPtr and above ROMBase. Not only does it seem pointless >to create a VBL desert anywhere in memory, but also the instruction waste >would be ludicrous, even for Apple :-). So it seems safe to say that >VBLs are safe above BufPtr. Anyone from Apple care to comment? Probably not, but I will. The situation I referred to was in the 64K (pre- Mac-Plus) ROM, and was fixed in the 128K (Mac Plus) ROM. It is of interest only to those who wish to be compatible with the old ROMs. >It also occurs to me that I have seen _VInstall and _VRemove in the .MPP or >.ATP driver, which are also in ROM. This is true in the 128K ROM, but not in the 64K ROM. -- Tim Maroney, Consultant, Eclectic Software, sun!hoptoad!tim "If you vote for clowns, you have no right to complain that only clowns make it to the ballot." -- Tim Maroney