Add input status register to the emulator

emulator.pas

@@ -8,9 +8,10 @@ program Emulator;
 {$define tape}
 {$define floppy}
 {$define modem}
+{$define status}
 {$endif}
 
-uses SysUtils, Crt{$ifdef modem}, Sockets{$endif};
+uses SysUtils, Crt{$ifdef modem}, Sockets{$endif}{$ifdef status}, BaseUnix{$endif};
 
 type
     {$ifdef tape}
@@ -70,7 +71,7 @@ var
     {$endif}
     Ch, Scan: ansichar; //Character for input and output and scancode for non-ASCII keys
     Verbose, IC, LFX: integer; //Verbose flag, instruction counter for CPU speed, and line feed position marker
-    Fetched{$ifdef floppy}, Disc0Track, Disc1Track, Disc0Sect, Disc1Sect{$endif}: byte; //Fetched byte, and disc drive locations
+    Fetched{$ifdef floppy}, Disc0Track, Disc1Track, Disc0Sect, Disc1Sect{$endif}: byte; //Fetched byte and disc drive locations
     {$ifdef floppy}
     DiscDrive: 0 .. 1; //Current disc drive number
     {$endif}
@@ -80,6 +81,9 @@ var
     ServerSocket: longint; //Server socket
     ServerAddr: TInetSockAddr; //Server address
     {$endif}
+    {$ifdef status}
+    FileDescs: TFDset; //File descriptor set
+    {$endif}
 
 //Terminal output
 procedure Output;
@@ -266,6 +270,46 @@ begin
         else B := 0;
     end
     {$endif}
+    {$ifdef status}
+    //Input status register
+    else if W = $fff8 then begin
+        {$ifndef fast}
+        wait (1);
+        {$endif}
+        //Initialise the register
+        B := 0;
+        //FFFF: Terminal
+        fpfd_zero (FileDescs);
+        fpfd_set (0, FileDescs);
+        if fpSelect (1, @FileDescs, nil, nil, 1) > 0 then B := B or 1;
+        //FFFE: No input
+        B := B or 2;
+        //FFFD: Tape reader or no input
+        B := B or 4;
+        //FFFC: Disc system data or no input
+        B := B or 8;
+        //FFFB: No input
+        B := B or $10;
+        //FFFA: Modem or no input
+        {$ifdef modem}
+        //Connect
+        CallServer;
+        //Check the connection
+        if Calling then begin
+            fpfd_zero (FileDescs);
+            fpfd_set (ServerSocket, FileDescs);
+            if fpSelect (ServerSocket + 1, @FileDescs, nil, nil, 0) > 0 then B := B or $20;
+        end;
+        {$endif}
+        {$ifndef modem}
+        B := B or $20;
+        {$endif}
+        //FFF9: No input
+        B := B or $40;
+        //FFF8: Input status register
+        B := B or $80;
+    end
+    {$endif}
     //Unused addresses
     else if W > LastRAM then B := 0
     //Regular load

readme.md

@@ -120,22 +120,23 @@ characters and non-character keys null.
 In Linux the emulator can be compiled with support for a character
 printer, an emulated high speed (roughly 500 CPS in and 50 CPS out)
 8-bit paper tape reader and punch, an emulated two-drive 8" floppy disc
-system, and a roughly 300 b/s modem with the arguments -dprinter,
+system, a roughly 300 b/s modem, and an input status register with the
--dtape, -dfloppy, and -dmodem respectively. Full 64 KiB of RAM and all
+arguments -dprinter, -dtape, -dfloppy, -dmodem, and -dstatus
-of these options can also be enabled with the argument -dfull. The
+respectively. Full 64 KiB of RAM and all of these options can also be
-printer is mapped to address FFFE, the tape reader and punch to FFFD,
+enabled with the argument -dfull. The printer is mapped to address FFFE,
-the disc system to FFFB and FFFC, and the modem to FFFA. The printer
+the tape reader and punch to FFFD, the disc system to FFFB and FFFC, the
-prints into /dev/usb/lp0. The tape files read from and punched to are
+modem to FFFA, and the input status register to FFF8. The printer prints
-(re)set using the program tapectl with the arguments -r and -p
+into /dev/usb/lp0. The tape files read from and punched to are (re)set
-respectively and the disc files in drives 0 and 1 using the program
+using the program tapectl with the arguments -r and -p respectively and
-floppyctl with the arguments -0 and -1 respectively. The disc system
+the disc files in drives 0 and 1 using the program floppyctl with the
-uses hard sectored single-sided discs with 77 tracks of 32 sectors of
+arguments -0 and -1 respectively. The disc system uses hard sectored
-137 bytes, or 337568 bytes in total: the disc files must be of this
+single-sided discs with 77 tracks of 32 sectors of 137 bytes, or 337568
-size. The modem is controlled by the program modemctl: the option -c is
+bytes in total: the disc files must be of this size. The modem is
-used to "call" an IP address and port, -a to set the modem ready for
+controlled by the program modemctl: the option -c is used to call an IP
-"answering" "calls" to port 1337, and -h to "hang". "Hanging" manually
+address and port, -a to set the modem ready for answering calls to port
-is not necessary when "calling" a different address or switching between
+1337, and -h to hang. Hanging manually is not necessary when making a
-"calling" and "answering". Note: "Answering" is not functional yet.
+new call or switching between calling and answering. Note: Answering is
+not implemented yet.
 
 The floppy disc system uses two ports: command at FFFB and data at FFFC.
 Only the low nibble of the command port is used, consisting of a
@@ -157,6 +158,11 @@ The commands for the disc system are:
  6: Read a sector from a disc to the buffer.
  7: Write a sector from the buffer to a disc.
 
+The input status register can be used to check if a device is ready to
+be read from. The reserved addresses FFF8-FFFF are mapped to the bits
+7-0: a set bit means either that the device is ready or that no input
+device is mapped to the address in question.
+
 The IPL loads the program specified as an argument when running the
 emulator.