Fix EGA scrolling for modes 0x0D and 0x0E

blog/2015/06/05/README.md

@@ -0,0 +1,180 @@
+The Strange Case of the EGA Graphics Scroll Bug 
+---
+
+For reasons I've forgotten, I was playing with different video modes in this
+[IBM PC AT w/EGA](/devices/pc/machine/5170/ega/640kb/rev1/) machine, and I discovered some odd problems.
+
+For example, run this code:
+
+	A>b:debug
+    -a
+    0CE0:0100  mov ax,e
+    0CE0:0103  int 10
+    0CE0:0105  int 3
+    0CE0:0106  
+    -g
+
+and the following "text" will appear at the top of the screen, in 640x200 16-color graphics mode 0x0E:
+
+    AX=0B01  BX=0000  CX=0000  DX=0000  SP=FFEE  BP=0000  SI=0000  DI=0000  
+    DS=0CE0  ES=0CE0  SS=0CE0  CS=0CE0  IP=0105   NV UP EI PL NZ NA PO NC 
+    0CE0:0105 CC            INT     3                                  
+    -
+
+If I typed "q", then "cls" and finally "dir", the screen would properly fill with DOS directory contents.
+However, as soon as the screen started to scroll, the screen contents became garbled.  Other EGA graphics modes,
+like 640x350 16-color mode 0x10, didn't have this problem.
+
+To investigate, I set a breakpoint in the IBM EGA ROM where the scrolling starts, at 0xC000:12EA (see p.130 of the
+"IBM Enhanced Graphics Adapter" Technical Reference document):
+
+	CRANK_A:
+		PUSH    CX
+		MOV     CL,DL
+		SUB     CH,CH
+		PUSH    SI
+		PUSH    DI
+		REP     MOVSB   
+		POP     DI
+		POP     SI
+		ADD     SI,BX
+		ADD     DI,BX
+		POP     CX
+		LOOP    CRANK_A
+
+CX arrives as 0xC0 (192), which is the number of scan-lines to move up, and BX is 0x50 (80), the number
+of bytes per scan-line.
+
+When the breakpoint was hit, I dumped the video hardware state, using the Debugger's "*d video*" command.
+For reference purposes, I've pasted the corresponding video state for mode 0x10 on the right-hand side.
+
+	breakpoint hit: C000:12EA (exec)
+	stopped (175707689 ops, 800060264 cycles, 133470 ms, 5994308 hz)
+	AX=020F BX=0050 CX=00C0 DX=1950 SP=0B58 BP=0511 SI=0280 DI=0000 
+	SS=011F DS=A000 ES=A000 PS=0246 V0 D0 I1 T0 S0 Z1 A0 P1 C0 
+	C000:12EA 51              PUSH     CX
+	
+	BIOSMODE: 0x0E                          BIOSMODE: 0x10
+	CRTC[0x00]: HORZ_TOTAL         0x70     CRTC[0x00]: HORZ_TOTAL         0x5B
+	CRTC[0x01]: HORZ_DISP_END      0x4F     CRTC[0x01]: HORZ_DISP_END      0x4F
+	CRTC[0x02]: HORZ_BLANK_START   0x59     CRTC[0x02]: HORZ_BLANK_START   0x53
+	CRTC[0x03]: HORZ_BLANK_END     0x2D     CRTC[0x03]: HORZ_BLANK_END     0x37
+	CRTC[0x04]: HORZ_RETRACE_START 0x5E     CRTC[0x04]: HORZ_RETRACE_START 0x52
+	CRTC[0x05]: HORZ_RETRACE_END   0x06     CRTC[0x05]: HORZ_RETRACE_END   0x00
+	CRTC[0x06]: VERT_TOTAL         0x04     CRTC[0x06]: VERT_TOTAL         0x6C
+	CRTC[0x07]: OVERFLOW           0x11     CRTC[0x07]: OVERFLOW           0x1F
+	CRTC[0x08]: PRESET_ROW_SCAN    0x00     CRTC[0x08]: PRESET_ROW_SCAN    0x00
+	CRTC[0x09]: MAX_SCAN_LINE      0x00     CRTC[0x09]: MAX_SCAN_LINE      0x00
+	CRTC[0x0A]: CURSOR_START       0x00     CRTC[0x0A]: CURSOR_START       0x00
+	CRTC[0x0B]: CURSOR_END         0x01     CRTC[0x0B]: CURSOR_END         0x01
+	CRTC[0x0C]: START_ADDR_HI      0x00     CRTC[0x0C]: START_ADDR_HI      0x00
+	CRTC[0x0D]: START_ADDR_LO      0x00     CRTC[0x0D]: START_ADDR_LO      0x00
+	CRTC[0x0E]: CURSOR_ADDR_HI     0x07     CRTC[0x0E]: CURSOR_ADDR_HI     0x01
+	CRTC[0x0F]: CURSOR_ADDR_LO     0x80*    CRTC[0x0F]: CURSOR_ADDR_LO     0x41*
+	CRTC[0x10]: VERT_RETRACE_START 0xE0     CRTC[0x10]: VERT_RETRACE_START 0x5E
+	CRTC[0x11]: VERT_RETRACE_END   0x23     CRTC[0x11]: VERT_RETRACE_END   0x2B
+	CRTC[0x12]: VERT_DISP_END      0xC7     CRTC[0x12]: VERT_DISP_END      0x5D
+	CRTC[0x13]: OFFSET             0x28     CRTC[0x13]: OFFSET             0x28
+	CRTC[0x14]: UNDERLINE          0x00     CRTC[0x14]: UNDERLINE          0x0F
+	CRTC[0x15]: VERT_BLANK_START   0xDF     CRTC[0x15]: VERT_BLANK_START   0x5F
+	CRTC[0x16]: VERT_BLANK_END     0xEF     CRTC[0x16]: VERT_BLANK_END     0x0A
+	CRTC[0x17]: MODE_CTRL          0xE3     CRTC[0x17]: MODE_CTRL          0xE3
+	CRTC[0x18]: LINE_COMPARE       0xFF     CRTC[0x18]: LINE_COMPARE       0xFF
+	   STATUS1: 0x01                           STATUS1: 0x01
+	   ATCDATA: true                           ATCDATA: true
+	 ATC[0x00]: PAL00    0x00                ATC[0x00]: PAL00    0x00
+	 ATC[0x01]: PAL01    0x01                ATC[0x01]: PAL01    0x01
+	 ATC[0x02]: PAL02    0x02                ATC[0x02]: PAL02    0x02
+	 ATC[0x03]: PAL03    0x03                ATC[0x03]: PAL03    0x03
+	 ATC[0x04]: PAL04    0x04                ATC[0x04]: PAL04    0x04
+	 ATC[0x05]: PAL05    0x05                ATC[0x05]: PAL05    0x05
+	 ATC[0x06]: PAL06    0x06                ATC[0x06]: PAL06    0x14
+	 ATC[0x07]: PAL07    0x07                ATC[0x07]: PAL07    0x07
+	 ATC[0x08]: PAL08    0x10                ATC[0x08]: PAL08    0x38
+	 ATC[0x09]: PAL09    0x11                ATC[0x09]: PAL09    0x39
+	 ATC[0x0A]: PAL0A    0x12                ATC[0x0A]: PAL0A    0x3A
+	 ATC[0x0B]: PAL0B    0x13                ATC[0x0B]: PAL0B    0x3B
+	 ATC[0x0C]: PAL0C    0x14                ATC[0x0C]: PAL0C    0x3C
+	 ATC[0x0D]: PAL0D    0x15                ATC[0x0D]: PAL0D    0x3D
+	 ATC[0x0E]: PAL0E    0x16                ATC[0x0E]: PAL0E    0x3E
+	 ATC[0x0F]: PAL0F    0x17                ATC[0x0F]: PAL0F    0x3F
+	 ATC[0x10]: MODE     0x01                ATC[0x10]: MODE     0x01
+	 ATC[0x11]: OVERSCAN 0x00                ATC[0x11]: OVERSCAN 0x00
+	 ATC[0x12]: PLANES   0x0F                ATC[0x12]: PLANES   0x0F
+	 ATC[0x13]: HORZPAN  0x00                ATC[0x13]: HORZPAN  0x00
+	 GRC[0x00]: SRESET   0x00                GRC[0x00]: SRESET   0x00
+	 GRC[0x01]: ESRESET  0x00                GRC[0x01]: ESRESET  0x00
+	 GRC[0x02]: COLORCMP 0x00                GRC[0x02]: COLORCMP 0x00
+	 GRC[0x03]: DATAROT  0x00                GRC[0x03]: DATAROT  0x00*
+	 GRC[0x04]: READMAP  0x00                GRC[0x04]: READMAP  0x00
+	 GRC[0x05]: MODE     0x11*               GRC[0x05]: MODE     0x00
+	 GRC[0x06]: MISC     0x05                GRC[0x06]: MISC     0x05
+	 GRC[0x07]: COLORDC  0x0F                GRC[0x07]: COLORDC  0x0F
+	 GRC[0x08]: BITMASK  0xFF                GRC[0x08]: BITMASK  0xFF
+	 SEQ[0x00]: RESET    0x03                SEQ[0x00]: RESET    0x03
+	 SEQ[0x01]: CLOCKING 0x01                SEQ[0x01]: CLOCKING 0x01
+	 SEQ[0x02]: MAPMASK  0x0F*               SEQ[0x02]: MAPMASK  0x0F*
+	 SEQ[0x03]: CHARMAP  0x00                SEQ[0x03]: CHARMAP  0x00
+	 SEQ[0x04]: MEMMODE  0x06                SEQ[0x04]: MEMMODE  0x06
+		  FEAT: 0x02	                          FEAT: 0x02
+		  MISC: 0x23	                          MISC: 0xA7
+	   STATUS0: 0x10                           STATUS0: 0x10
+	   LATCHES: 0x00000000                     LATCHES: 0x00000000
+		ACCESS: 0x1411                          ACCESS: 0x0400
+
+One of the apparent oddities is that, for mode 0x0E, GRC[MODE] has been programmed with 0x11, whereas
+for mode 0x10, it was programmed with 0x00.  Why would mode 0x0E want to set the ODDEVEN bit during the scroll,
+when it hadn't been set during any other writes to the screen?
+
+At this point, I dumped the instruction history buffer a bit ("*dh 100*"), and noticed this GRC write:
+
+	C000:1582 8BC5            MOV      AX,BP                ;history=33
+	C000:1584 B603            MOV      DH,03                ;history=32
+	C000:1586 B2CE            MOV      DL,CE                ;history=31
+	C000:1588 E88AF7          CALL     0D15                 ;history=30
+	C000:0D15 86C4            XCHG     AL,AH                ;history=29
+	C000:0D17 EE              OUT      DX,AL                ;history=28
+	C000:0D18 42              INC      DX                   ;history=27
+	C000:0D19 86C4            XCHG     AL,AH                ;history=26
+	C000:0D1B EE              OUT      DX,AL                ;history=25
+	C000:0D1C 4A              DEC      DX                   ;history=24
+
+So I looked back farther and saw where BP was set:
+
+	C000:1522 BA00A0          MOV      DX,A000              ;history=97
+	C000:1525 BD1105          MOV      BP,0511              ;history=96
+
+Here's the complete function:
+
+	GR_ST_1:
+		MOV     DX,A000
+		MOV     BP,0511
+		CMP     AH,0F
+		JC      1535
+		CALL    14F7
+		JNC     1535
+		MOV     BP,0501
+		RET     
+
+OK, so any (EGA) graphics mode below 0x0F is going to the trigger the use of Write Mode 1 with the ODDEVEN bit set.
+And sure enough, the scrolling bug also occurs when using 320x200 16-color mode 0x0D.
+
+It's also worth noting that, whenver the ODDEVEN bit of the GRC Mode Register is set, the SEQUENTIAL bit in the Sequencer
+Memory Mode Register is supposed to be clear (and vice versa -- those two bits are always supposed to be oppositely set).
+But here, the IBM EGA BIOS hasn't done that.  One wonders if that was a mistake....
+
+Another bit of trivia: while dumping the frame buffer in a VGA text mode in a different emulator, I discovered that
+if I turned off the ODDEVEN bit in the GRC Mode Register, odd bytes would still appear from plane 1; it wasn't until I
+*also* turned off the CHAIN bit in the GRC Miscellaneous Register that the odd bytes would no longer appear.  But,
+that could have just been an idiosyncrasy of that particular emulator.
+
+As a result of all these observations, and more importantly, to make EGA scrolling work properly in modes 0x0D and 0x0E,
+I've changed the Video component to use odd/even memory functions *only* when the SEQUENTIAL bit (bit 2) of the
+Sequencer's Memory Mode Register is clear, instead of relying on the ODDEVEN bit (bit 4) of the Graphics Controller's Mode
+Register.
+
+To be continued....  because I've barely scratched the surface of all the side-effects of EGA/VGA odd/even addressing,
+and I hope to do some testing on real hardware in the near future.
+
+*[@jeffpar](http://twitter.com/jeffpar)*  
+*June 5, 2015*

devices/pc/machine/README.md

@@ -1,12 +1,18 @@
 IBM PC Machine Configurations
 ---
 
-Here you'll find sample Machine Configurations for all the IBM PC models that PCjs currently supports.
+PCjs supports the following IBM PC models:
 
 * [Model 5150](/devices/pc/machine/#model-5150-machine-configurations)
 * [Model 5160](/devices/pc/machine/#model-5160-machine-configurations)
 * [Model 5170](/devices/pc/machine/#model-5170-machine-configurations)
 
+Configurations for the [Challenger 1P](/devices/c1p/machine/) and other non-IBM machines are available [here](/devices/).
+
+Support is also being added for a few IBM PC-compatible machines, starting with the [Compaq DeskPro 386](compaq/deskpro386/) series.
+
+---
+
 ### Model 5150 Machine Configurations
 
 * [IBM PC, MDA, 64K](/devices/pc/machine/5150/mda/64kb/)

modules/htmlout/lib/htmlout.js

@@ -240,6 +240,8 @@ var asFilesNonServed = [
     "web.config"        // Azure/IISNode-specific
 ];
 
+var nBlogExcerpts = 20;
+
 /**
  * HTMLOut()
  *
@@ -1167,10 +1169,10 @@ HTMLOut.prototype.getBlog = function(sToken, sIndent, aParms)
              * strings) that can hold the excerpts.  We'll plug the excerpts into aExcerpts as they
              * come in, and then we'll assemble them all at the end.
              *
-             * We also take this opportunity to cap the number of (most recent) excerpts at 10.
+             * We also take this opportunity to cap the number of (most recent) excerpts.
              */
             var i;
-            var cExcerpts = Math.min(asPaths.length, 10);
+            var cExcerpts = Math.min(asPaths.length, nBlogExcerpts);
             var aExcerpts = new Array(cExcerpts);
             var cExcerptsRemaining = aExcerpts.length;
             for (i = 0; i < cExcerpts; i++) {

modules/pcjs/lib/debugger.js

@@ -4499,7 +4499,7 @@ if (DEBUGGER) {
             this.println("\ninput commands:");
             this.println("\ti [p]\tread port [p]");
             /*
-             * NOTE: Regarding this warning, it might be nice if we had an "unchecked" version of
+             * TODO: Regarding this warning, consider adding an "unchecked" version of
              * bus.checkPortInputNotify(), since all Debugger memory accesses are unchecked, too.
              *
              * All port I/O handlers ARE aware when the Debugger is calling (addrFrom is undefined),
@@ -4796,7 +4796,7 @@ if (DEBUGGER) {
             this.println("\noutput commands:");
             this.println("\to [p] [b]\twrite byte [b] to port [p]");
             /*
-             * NOTE: Regarding this warning, it might be nice if we had an "Unchecked" version of
+             * TODO: Regarding this warning, consider adding an "unchecked" version of
              * bus.checkPortOutputNotify(), since all Debugger memory accesses are unchecked, too.
              *
              * All port I/O handlers ARE aware when the Debugger is calling (addrFrom is undefined),

modules/pcjs/lib/video.js

@@ -1342,7 +1342,7 @@ Card.SEQ = {
         SELB_HIGH:          0x10,       // VGA only
         SELA_HIGH:          0x20        // VGA only
     },
-    MODE: {
+    MEMMODE: {
         INDX:               0x04,       // Sequencer Memory Mode Register
         ALPHA:              0x01,       // set for alphanumeric (A/N) mode, clear for graphics (APA or "All Points Addressable") mode (EGA only)
         EXT:                0x02,       // set if memory expansion installed, clear if not installed
@@ -1352,7 +1352,7 @@ Card.SEQ = {
     TOTAL_REGS:             0x05
 };
 
-if (DEBUGGER) Card.SEQ.REGS = ["RESET","CLOCKING","MAPMASK","CHARMAP","MODE"];
+if (DEBUGGER) Card.SEQ.REGS = ["RESET","CLOCKING","MAPMASK","CHARMAP","MEMMODE"];
 
 /*
  * VGA Digital-to-Analog Converter (DAC) Registers (regDACMask, regDACState, regDACAddr, and regDACData)
@@ -1507,8 +1507,8 @@ if (DEBUGGER) Card.GRC.REGS = ["SRESET","ESRESET","COLORCMP","DATAROT","READMAP"
  *
  * Even/Odd Memory Access Functions
  *
- * The "EVENODD" functions deal with the EGA's default text-mode addressing, where every EVEN address is mapped to
+ * The "EVENODD" functions deal with the EGA's default text-mode addressing, where EVEN addresses are mapped to
- * plane 0 (and plane 2) and every ODD address is mapped to plane 1 (and plane 3).  This occurs when SEQ.MODE.SEQUENTIAL
+ * plane 0 (and 2) and ODD addresses are mapped to plane 1 (and 3).  This occurs when SEQ.MEMMODE.SEQUENTIAL
  * is clear (and GRC.MODE.EVENODD is set), turning address bit 0 (A0) into a "plane select" bit.  Whether A0 is
  * also used as a memory address bit depends on CRTC.MODE_CTRL.BM: if it's set, then we're in "Byte Mode" and A0 is
  * used as-is; if it's clear, then we're in "Word Mode", and either A15 (when CRTC.MODE_CTRL.AW is set) or A13
@@ -1599,6 +1599,11 @@ Card.ACCESS.readByteMode0 = function readByteMode0(off, addr)
  */
 Card.ACCESS.readByteMode0EvenOdd = function readByteMode0EvenOdd(off, addr)
 {
+    /*
+     * TODO: As discussed in getAccess(), we need to run some tests on real EGA/VGA hardware to determine
+     * exactly what gets latched (ie, from which address) when EVENODD is in effect.  Whatever we learn may
+     * also dictate a special EVENODD function for Read Mode 1 as well.
+     */
     off += this.offset;
     var idw = off & ~0x1;
     var dw = this.controller.latches = this.adw[idw];
@@ -1821,6 +1826,10 @@ Card.ACCESS.writeByteMode1 = function writeByteMode1(off, b, addr)
  */
 Card.ACCESS.writeByteMode1EvenOdd = function writeByteMode1EvenOdd(off, b, addr)
 {
+    /*
+     * TODO: As discussed in getAccess(), we need to run some tests on real EGA/VGA hardware to determine
+     * exactly where latches are written (ie, to which address) when EVENODD is in effect.
+     */
     off += this.offset;
     //
     // When even/odd addressing is enabled, nWriteMapMask must be cleared for planes 1 and 3 if
@@ -2225,9 +2234,9 @@ Card.prototype.dumpCard = function()
             this.dumpRegs("      FEAT", this.regFeat);
             this.dumpRegs("      MISC", this.regMisc);
             this.dumpRegs("   STATUS0", this.regStatus0);
-            this.dumpRegs("   LATCHES", this.latches);
+            this.dbg.println("   LATCHES: 0x" + str.toHex(this.latches));
             this.dbg.println("    ACCESS: " + str.toHexWord(this.nAccess));
-            this.dbg.println("Use 'dump video buffer' to dump video memory");
+            this.dbg.println("Use 'dump video [addr]' to dump video memory");
             /*
              * There are few more EGA regs we could dump, like GRCPos1, GRCPos2, but does anyone care?
              */
@@ -3836,9 +3845,38 @@ Video.prototype.getAccess = function()
         if (regGRCMode & Card.GRC.MODE.READ_MODE1) {
             nReadAccess = Card.ACCESS.READ.MODE1;
         }
-        if (regGRCMode & Card.GRC.MODE.EVENODD) {
+        /*
-            nReadAccess |= Card.ACCESS.READ.EVENODD;
+         * I discovered that when the IBM EGA ROM scrolls the screen in graphics modes 0x0D and 0x0E, it
-            nWriteAccess |= Card.ACCESS.WRITE.EVENODD;
+         * reprograms this register for WRITE_MODE1 (which is fine) *and* EVENODD (which is, um, very odd).
+         * Moreover, it does NOT make the complementary change to the SEQ.MEMMODE.SEQUENTIAL bit; under
+         * "normal" circumstances, those two bits are always supposed to programmed oppositely.
+         *
+         * Until I can perform some tests on real hardware, I have to assume that the EGA scroll operation
+         * is supposed to actually WORK in modes 0x0D and 0x0E, so I've decided to tie the trigger for my own
+         * EVENODD functions to SEQ.MEMMODE.SEQUENTIAL being clear, instead of GRC.MODE.EVENODD being set.
+         *
+         * It's also possible that my EVENODD read/write functions are not implemented properly; when EVENODD
+         * is in effect, which addresses get latched by a read, and to which addresses are latches written?
+         * If EVENODD has no effect on the effective address used with the latches, then I should change the
+         * EVENODD read/write functions accordingly.
+         *
+         * However, I've also done some limited testing with an emulated VGA running in text mode, and I've
+         * discovered that toggling the GRC.MODE.EVENODD bit *alone* doesn't seem to affect the delivery of
+         * text mode attributes from plane 1.  So maybe this is the wiser change after all.
+         *
+         * TODO: Perform some tests on actual EGA/VGA hardware, to determine the proper course of action.
+         *
+         *  if (regGRCMode & Card.GRC.MODE.EVENODD) {
+         *      nReadAccess |= Card.ACCESS.READ.EVENODD;
+         *      nWriteAccess |= Card.ACCESS.WRITE.EVENODD;
+         *  }
+         */
+        var regSEQMode = card.regSEQData[Card.SEQ.MEMMODE.INDX];
+        if (regSEQMode != null) {
+            if (!(regSEQMode & Card.SEQ.MEMMODE.SEQUENTIAL)) {
+                nReadAccess |= Card.ACCESS.READ.EVENODD;
+                nWriteAccess |= Card.ACCESS.WRITE.EVENODD;
+            }
         }
         nAccess = nReadAccess | nWriteAccess;
     }
@@ -5157,8 +5195,15 @@ Video.prototype.outSEQData = function(port, bOut, addrFrom)
         }
         this.cardEGA.regSEQData[this.cardEGA.regSEQIndx] = bOut;
     }
-    if (this.cardEGA.regSEQIndx == Card.SEQ.MAPMASK.INDX) {
+    switch(this.cardEGA.regSEQIndx) {
+    case Card.SEQ.MAPMASK.INDX:
         this.cardEGA.nWriteMapMask = Video.aEGAByteToDW[bOut & Card.SEQ.MAPMASK.MAPS];
+        break;
+    case Card.SEQ.MEMMODE.INDX:
+        this.setAccess(this.getAccess());
+        break;
+    default:
+        break;
     }
 };
 

modules/shared/templates/common.html

@@ -22,7 +22,7 @@
 						<li><a href="/">Home</a></li>
 						<li><a href="/apps/pc/">Apps</a></li>
 						<li><a href="/disks/pc/">Disks</a></li>
-						<li><a href="/devices/">Machines</a></li>
+						<li><a href="/devices/pc/machine/">Machines</a></li>
 						<li><a href="/docs/">Docs</a></li>
 						<li><a href="/pubs/">Pubs</a></li>
 						<li><a href="/blog/">Blog</a></li>

modules/shared/templates/common.xsl

@@ -22,7 +22,7 @@
 					<li><a href="/">Home</a></li>
 					<li><a href="/apps/pc/">Apps</a></li>
 					<li><a href="/disks/pc/">Disks</a></li>
-					<li><a href="/devices/">Machines</a></li>
+					<li><a href="/devices/pc/machine/">Machines</a></li>
 					<li><a href="/docs/">Docs</a></li>
 					<li><a href="/pubs/">Pubs</a></li>
 					<li><a href="/blog/">Blog</a></li>

versions/c1pjs/1.18.2/common.xsl

@@ -20,7 +20,7 @@
 					<li><a href="/">Home</a></li>
 					<li><a href="/apps/pc/">Apps</a></li>
 					<li><a href="/disks/pc/">Disks</a></li>
-					<li><a href="/devices/">Machines</a></li>
+					<li><a href="/devices/pc/machine/">Machines</a></li>
 					<li><a href="/docs/">Docs</a></li>
 					<li><a href="/pubs/">Pubs</a></li>
 					<li><a href="/blog/">Blog</a></li>

versions/pcjs/1.18.2/common.xsl

@@ -20,7 +20,7 @@
 					<li><a href="/">Home</a></li>
 					<li><a href="/apps/pc/">Apps</a></li>
 					<li><a href="/disks/pc/">Disks</a></li>
-					<li><a href="/devices/">Machines</a></li>
+					<li><a href="/devices/pc/machine/">Machines</a></li>
 					<li><a href="/docs/">Docs</a></li>
 					<li><a href="/pubs/">Pubs</a></li>
 					<li><a href="/blog/">Blog</a></li>