Babb Feeds Back

By Gareth Babb

Originally published in EUG #22

This is a big letter as it's two issues' worth. I forgot I had written one letter and then of course forgot to post it.

Re: John Crane. *BYE closes any open (ADFS) files and parks any Hard Drive heads, whereas *CLOSE just closes any open files.

Re: Derek Walker. Here's a small bit of code to completely compact:-

      DIM data &100
      FOR N=4 TO 7 STEP 3
      [OPT N
      LDA #218:LDX #0:LDY #0:JSR &FFF4
      LDA #3:LDX #20:JSR &FFF4
      LDA #23:JSR &FFCB:LDA #1:JSR &FFCB
      LDA #0:LDY #8:.curs:JSR &FFCB:DEY:BNE curs
      LDA #3:JSR &FFF4
      LDA #0
      STA &1D00
      STA &1D01:LDA #&20:STA &1D02
      LDA #130:JSR &FFF4:STX &1D03:STY &1D04
      LDA #8:STA &1D05
      LDA #0:STA &1D06:STA &1D07:STA &1D08:STA &1D09:STA &1D0A
      STA &1D0B:STA &1D0D:STA &1D0E
      LDA #2:STA &1D0C

      LDX #0:LDY #&1D:LDA #&72:JSR &FFF1
      LDA &1D00:BEQ okay
      BRK:BRK:EQUS "Bugger":BRK

      BIT &FF:BMI end_it

      LDA &21FE:CMP #3:BNE compact_it

      LDX #map MOD 256:LDY #map DIV 256:JSR &FFF7

      LDA #218:LDX #0:LDY #0:JSR &FFF4
      LDA #3:LDX #20:JSR &FFF4
      LDA #23:JSR &FFCB
      LDA #0:LDY #7:.curs2:JSR &FFCB:DEY:BNE curs2
      LDA #3:JMP &FFF4

      LDX #map MOD 256:LDY #map DIV 256:JSR &FFF7
      LDX #Computer_Games_To_Play_And_Writeact MOD 256:LDY #Computer_Games_To_Play_And_Writeact DIV 256:JSR &FFF7
      JMP loop

      .map:EQUS "Map":EQUB 13
      .compact:EQUS "Compact 1D 63":EQUB 13
      OSCLI "Save EFC "+STR$data+" "+STR$O%+" C00 C00"

Um, ADFS doesn't use NMIs - though it does claim NMI workspace - or IRQs for anything. For both floppy and Hard Drive, it polls (Which is why for floppy it will disable IRQs and change screen mode, disabling the palette at the same time. Otherwise the 177x will flag overruns!). The normal ST506/SASI HD interface will wait for the computer to take data as fast as it can, which is why ADFS doesn't have to change screen mode or bother with disabling IRQs.

On the BBC, NMIs are only used for floppy and even then all code is run from &D00; the pace specifically reserved for NMI code. A loop in (A)DFS itself just keeps check on a flag byte which the NMI routine updates to flag when data transfer from the 177x has finished.

I presume that Acorn didn't use NMIs on the Elk due to the problems with claiming and releasing memory from the ULA - on the Acorn Plus 3, bit 4 of the ctrl reg is connected straight to the NMI line, except that is isn't because Link 1 is not made by default, so a NMI can be forced. ADI from Pres requires the enabling of this link on the Acorn Plus 3, as that does use NMIs (I presume mainly to keep the Mode 0 display - though it does break up a bit as the ULA is forced to release memory in the middle of screen refreshes!)

Re: Gus Donnachaidh. Why not get someone to write a 64K compatible screen loader? You could even compress the screens at the same time.

I find the best way to clean contacts is with a soft rubber.

You forgot to mention two codes that don't change for phoneday. Basically all non-geographic codes (e.g. 0800, 0891, 0645 etc) remain the same, except for most pager numbers (The oddity is the Hutchinson Display Paging which remains on 0941-1). Oh yeah, and the change from 010 to 00 for international access.

Boo! Down with Anderson Country/Afternoon Shift. Get it off!

On the Internet: 386 and a Fax Modem? No needy. You can get away with anything you want for normal e-mail access. I use a 286 for e-mail (The only thing I use it for!). Even KA9Q (A well known PD TCPIP program) will run happily on a 286 to give you telnet, ftp, e-mail, etc. It's only when you start going for WWW (overrated) and need the graphics that WINDOWS (and thus the processing power needed) comes into play.

Alternatively, get a decent computer. I believe a company called Acorn produce some...

Look out for local Bulletin Boards which will provide e-mail/newsgroup access for nothing/small fee. Otherwise full internet operators are providing quite extensive coverage nowadays (e.g. www, telnet, ftp).

Re: Gerry Emson. What you have there is a standard PC serial mouse. No good for the Elk unless you find a serial port and write your own software. No existing software will support it. Sell it and hunt out an old user port (for example AMX) mouse.

I've ran an Elk from a 12v power supply no problem. A car battery shouldn't be much different. This was going through the normal power circuitry stage - it copes, so no need to produce -5v yourself. (What use is that anyway? I think it just goes straight to the edge connector?)

Gareth Babb, EUG #22