On 25 Jan 2013, at 10:47, Norman Dunbar wrote: > Morning all, > > I'm doing a bit more work on the next exciting episode of QL Today's LibGen > utility. I have spotted a huge pair of bugs in my code, viz: > > > li_libfile equ $03 > ... > > li_unav move.l #$11111111,ws_litem+li_libfile(a1) > bra.s li_rdrw > ... > li_avail move.l #$01011101,ws_litem+li_libfile(a1) > li_rdrw moveq #-1,d3 > jmp wm_ldraw(a2) > > The idea was to set 4 consecutive loose item status bytes to unavailable > (#wsi_mkun) in the first case, and to set three of them to available > (#wsi_mkav) and one to unavailable (#wsi_mkun) in the second case. > > The code above is a huge problem because li_libfile is odd, A1 is even as is > ws_litem at $40. I would expect an address exception at the very least. > > Running the code under QMON2 shows that I'm attempting to store a long word > at $43(a1) where a1 is $4ABBA6. That works out at $4ABBE9 which is most > definitely odd. > > In QPC, version 3.33, the above works without any exceptions. PRINT PROCESSOR > gives 20, I must assume that either a 68020 doesn't barf at a long word > access to an odd address or something is not working correctly any more! > > I've checked and rechecked my paper and pdf copies of the Motorola processor > manual, and there is no mention that you can do a long move to an odd address. > > I'm not running any "monitor" code that would intercept the address > exceptions and quietly swallow it. > > I have stepped through the code for both, and it works, the MOVE.L is carried > out, after executing the code at li_avail, I can see the following results at > $43(a1) in QMON2: > > QMON> d $43(a1) 4 > 4ABBE9 0101 0101 004E FF6F .....NV. > > Is it any wonder I'm confused? > > What am I missing? > > > Cheers, > Norm. > >
An address error occurs if an attempt is made to fetch an instruction from an odd address. As far as I know the 680020+ machines allow long and word fetches from odd addresses - they simply take longer than if the address is on a word boundary. George _______________________________________________ QL-Users Mailing List http://www.q-v-d.demon.co.uk/smsqe.htm
