diff --git a/.vscode/settings.json b/.vscode/settings.json
index 88b8fc7..487c8cc 100644
--- a/.vscode/settings.json
+++ b/.vscode/settings.json
@@ -1,7 +1,4 @@
 {
-    "esbonio.sphinx.buildDir": "${workspaceFolder}/docs/build",
-    "esbonio.sphinx.confDir": "${workspaceFolder}/docs/source",
-    "esbonio.sphinx.srcDir": "${workspaceFolder}/docs/source",
     "restructuredtext.linter.doc8.extraArgs": [
         "--ignore D001"
     ],
diff --git a/docs/source/index.rst b/docs/source/index.rst
index e9b826a..31f12e9 100644
--- a/docs/source/index.rst
+++ b/docs/source/index.rst
@@ -27,11 +27,11 @@ Key Features
 - **64KB System RAM**
 - **64KB Extended RAM**
 - **VGA and HD Output**
-- **8-Channel Stereo Sound Generator**
+- **Yamaha OPL2 FM Sound Generator**
 - **Protected Operating System**
 - **USB** for Keyboard, Mouse, Gamepads, and Storage
 - **Bluetooth LE** for Keyboard, Mouse, and Gamepads
-- **WiFi** modem emulation
+- **WiFi** Hayes modem emulation
 - **Real Time Clock** with DST and NTP
 
 
diff --git a/docs/source/os.rst b/docs/source/os.rst
index a2cc064..79b3252 100644
--- a/docs/source/os.rst
+++ b/docs/source/os.rst
@@ -531,6 +531,52 @@ CLOCK_GETRES
    :errno: EINVAL
 
 
+TZSET
+-----
+
+.. c:function:: int void tzset(void);
+.. c:function:: int f_tzset (struct _tzset *tz)
+
+   .. code-block:: c
+
+      struct _tzset
+      {
+         int8_t daylight;  /* non 0 if daylight savings time active */
+         int32_t timezone; /* Number of seconds behind UTC */
+         char tzname[5];   /* Name of timezone, e.g. CET */
+         char dstname[5];  /* Name when daylight true, e.g. CEST */
+      };
+
+   The virtual f_tzset() is the how tzset() is implemented. Use `help set tz` on the
+   monitor to learn about configuring your time zone.
+
+   :Op code: RIA_OP_TZSET 0x0D
+   :C proto: time.h
+   :returns: 0 on success. -1 on error.
+   :errno: EINVAL
+
+
+TZQUERY
+-------
+
+.. c:function:: struct tm *localtime(const time_t *timep);
+.. c:function:: int f_tzquery (uint32_t time, struct _tzquery *dst)
+
+   .. code-block:: c
+
+      struct _tzquery
+      {
+         int8_t daylight;  /* non 0 if daylight savings time active */
+      };
+
+   The virtual f_tzquery() is part of how localtime() is implemented.
+
+   :Op code: RIA_OP_TZQUERY 0x0E
+   :C proto: time.h
+   :returns: Seconds to add to UTC for localtime.
+   :errno: will not fail
+
+
 CLOCK_GETTIME
 -------------
 
@@ -564,37 +610,6 @@ CLOCK_SETTIME
    :a regs: return, clock_id
    :errno: EINVAL, EUNKNOWN
 
-
-CLOCK_GETTIMEZONE
------------------
-
-.. c:function:: int clock_gettimezone (uint32_t time, clockid_t clock_id, struct _timezone *tz)
-
-   .. code-block:: c
-
-      struct _timezone
-      {
-         int8_t daylight;  /* >0 if daylight savings time active */
-         int32_t timezone; /* Number of seconds behind UTC */
-         char tzname[5];   /* Name of timezone, e.g. CET */
-         char dstname[5];  /* Name when daylight true, e.g. CEST */
-      };
-
-   Returns a cc65 _timezone structure for the requested time. Use
-   `help set tz` on the monitor to learn about configuring your time zone.
-
-   *** Experimental *** time zones in cc65 are incomplete probably because no
-   other 6502 OS supports them.
-
-   :Op code: RIA_OP_CLOCK_GETTIMEZONE 0x13
-   :C proto: None, Experimental
-   :param time: time_t compatible integer.
-   :param clock_id: 0 for CLOCK_REALTIME.
-   :returns: 0 on success. -1 on error.
-   :a regs: return, clock_id
-   :errno: EINVAL
-
-
 OPEN
 ----
 
diff --git a/docs/source/ria.rst b/docs/source/ria.rst
index 130a6a6..a1646c7 100644
--- a/docs/source/ria.rst
+++ b/docs/source/ria.rst
@@ -199,25 +199,6 @@ backwards and reverse data. These adders allow for very fast sequential
 access, which typically makes up for the slightly slower random access
 compared to 6502 system RAM.
 
-RW0 and RW1 are latching. This is important to remember when other
-systems change XRAM. For example, when using read_xram() to load XRAM
-from a mass storage device, this will not work as expected:
-
-.. code-block:: C
-
-  RIA.addr0 = 0x1000;
-  read_xram(0x1000, 1, fd);
-  uint8_t result = RIA.rw0; // wrong
-
-Setting ADDR after the expected XRAM change will latch RW to the
-latest value.
-
-.. code-block:: C
-
-  read_xram(0x1000, 1, fd);
-  RIA.addr0 = 0x1000;
-  uint8_t result = RIA.rw0; // correct
-
 Extended Stack (XSTACK)
 -----------------------
 
@@ -697,3 +678,27 @@ Volume attenuation is logarithmic.
      - 8s
      - 24s
      - 0/256 (silent)
+
+
+Yamaha OPL2 FM Sound Generator
+==============================
+
+The RIA includes a YM3812 FM Sound Generator (OPL2). It is configured
+with extended register device 0 channel 1 address 0x01.
+
+Enable and disable the RIA OPL2 by setting the extended register. The
+extended register value is the XRAM start address for the 256 OPL2
+registers. The OPL2 registers must begin on a page boundary.
+
+.. code-block:: C
+
+  xreg(0, 1, 0x01, xaddr); // enable
+  xreg(0, 1, 0x01, 0xFFFF); // disable
+
+If, for example, xaddr is 0x4200 then the 256 registers of an OPL2 chip
+are mapped into XRAM from 0x4200 to 0x42FF. Consult 
+
+Timers, interrupts, and the status register are not supported and were
+not widely used. These were in Yamaha OPL chips to assist with cost
+reducing consumer devices and rarely used in computers which had their
+own timers.