VM2 byte write without RMW

[xolod79]

VM2 byte write without RMW. In wb_plm.v simple change:

assign p[26] = cmp(rq[15:0], 16'b0001xxxxxxxxxxxx); to assign p[26] = cmp(rq[15:0], 16'bx001xxxxxxxxxxxx); // WTBT no RMW

Probably it is worth making a parameter during assembly for selection. Work is checked on DVK in RT11 and Soyuz Neon. Сorrection author Alexey Kisly.

[1801BM1]

How "movb" works on original LSI-11:

How "movb" works on M4:

How "movb" works on F-11:

Why should we change this behavior ? It seems it was intended to have the same as DEC did. Single write "movb also might have side effects on some I/O. Should this change be merged? Not sure, because of it impacts original DEC compatibility. Keeping the latter was the objective of BM2 developers.