Ready to release v1.15.5 (I think)

blog/2014/10/17/README.md

@@ -0,0 +1,49 @@
+Release of PCjs v1.15.5
+---
+
+The [IBM PC AT "Rev 3"](/configs/pc/machines/5170/ega/1152kb/rev3/) machine configuration boots in
+v1.15.5 of PCjs now, which includes the following fixes:
+
++ The BIOS expects memory refresh to occur roughly every 16us, which I've resolved by tying the state
+of the refresh bit in port 0x61 to bit 6 of the CPU cycle count (see *in8042RWReg()* in [chipset.js](/my_modules/pcjs-client/lib/chipset.js));
+the original AT BIOS was satisfied with a refresh bit that merely alternated, whereas the new AT BIOS
+is much more particular about the rate at which that bit changes, since many hard-coded delay-loops have
+now been replaced with code that waits for a specific number of refresh cycles. 
++ The 8042 Keyboard Controller emulation needed a few more tweaks, mainly with respect to what happens
+when the keyboard's "clock" line is toggled (see *set8042CmdData()* in [chipset.js](/my_modules/pcjs-client/lib/chipset.js)).
++ The Floppy Disk Controller needed to add support for the "READ ID" command, in order for the BIOS
+"double-stepping" test to work (double-stepping is required on an 80-track drive when attempting to read
+a 40-track diskette).
++ The BIOS Diskette Reset function does something odd after resetting the Floppy Disk Controller: it
+issues not one but *four* "SENSE INTERRUPT STATUS" commands to the FDC, and expects each response to
+return an incrementally larger drive number.  I found this a bit mystifying, considering that the IBM's
+own FDC/HDC "combo card" supports a maximum of *two* diskette drives.  But, there's no point in arguing
+with a BIOS that's almost 30 years old.
++ The BIOS attempts to detect what its authors must have considered a common problem: failure to run SETUP
+after installing a second hard drive.  So, when the CMOS reports only one hard drive installed, the BIOS
+probes for a second hard drive anyway, and it does so by simply writing the drive number to the ATC's "DRVHD"
+register and then immediately reading the "STATUS" register, without issuing any intervening command.
+It was an easy fix to *outATCDrvHd()* in [hdc.js](/my_modules/pcjs-client/lib/hdc.js), but I was surprised
+to discover that the ATC had this behavior, and now I'm wondering how many other I/O operations require
+immediate "STATUS" register updates.
+
+This PCjs release also fixes a problem reported by a user: if you disable **localStorage** support in your
+browser, previous versions would fault.  I knew that every browser that supports PCjs also supports
+**localStorage**, but I didn't consider what might happen if a user had decided to turn it off.
+
+The only downside to turning off **localStorage** is that none of your PCjs machines will be able save/restore
+their state when you leave/return to the page, so they will always reboot.
+
+Browser's don't always refer to the **localStorage** feature by its actual name, either.  For example, in
+Chrome, the setting that enables/disables **localStorage** is hidden under "Advanced Settings" => "Privacy" =>
+"Content Settings" => "Cookies" => "Allow local data to be set (recommended)".  Which is a little misleading
+and annoying, because **localStorage** != **cookie**.
+
+PCjs *never* sets any cookies.  Cookies are bits of data that your browser saves and then automatically sends
+off to the server every time you make a request.  **localStorage** is nothing more than local storage.  Granted,
+a JavaScript application could certainly abuse it and send it around like a cookie, but PCjs doesn't do that.
+The only exception is when PCjs detects a problem, and even then, you must first agree to submit your machine's
+state as part of the bug report.
+
+*[@jeffpar](http://twitter.com/jeffpar)*  
+*October 17, 2014*