Improve -B bitclock documentation

src/avrdude.1

@@ -332,18 +332,20 @@ programmed in high-voltage serial mode.
 Override the RS-232 connection baud rate specified in the respective
 programmer's entry of the configuration file.
 .It Fl B Ar bitclock
-Specify the bit clock period for the JTAG interface or the ISP clock (JTAG ICE only).
-The value is a floating-point number in microseconds.
-Alternatively, the value might be suffixed with "Hz", "kHz", or "MHz",
-in order to specify the bit clock frequency, rather than a period.
-The default value of the JTAG ICE results in about 1 microsecond bit
-clock period, suitable for target MCUs running at 4 MHz clock and
-above.
-Unlike certain parameters in the STK500, the JTAG ICE resets all its
-parameters to default values when the programming software signs
-off from the ICE, so for MCUs running at lower clock speeds, this
-parameter must be specified on the command-line.
+Specify the bit clock period for the JTAG, PDI, TPI, UPDI, or ISP
+interface. The value is a floating-point number in microseconds.
+Alternatively, the value might be suffixed with "Hz", "kHz" or
+"MHz" in order to specify the bit clock frequency rather than a
+period. Some programmers default their bit clock value to a 1
+microsecond bit clock period, suitable for target MCUs running at 4
+MHz clock and above. Slower MCUs need a correspondingly higher bit
+clock period. Some programmers reset their bit clock value to the
+default value when the programming software signs off, whilst others
+store the last used bit clock value. It is recommended to always
+specify the bit clock if read/write speed is important.
 You can use the 'default_bitclock' keyword in your
+.Pa ${HOME}/.config/avrdude/avrdude.rc
+or
 .Pa ${HOME}/.avrduderc
 file to assign a default value to keep from having to specify this
 option on every invocation.
@@ -357,6 +359,8 @@ through the use of a config file to make
 work with different programmers as long as the programmer supports the
 Atmel AVR serial program method.  You can use the 'default_programmer'
 keyword in your
+.Pa ${HOME}/.config/avrdude/avrdude.rc
+or
 .Pa ${HOME}/.avrduderc
 file to assign a default programmer to keep from having to specify
 this option on every invocation.

src/doc/avrdude.texi

@@ -440,19 +440,21 @@ Override the RS-232 connection baud rate specified in the respective
 programmer's entry of the configuration file.
 
 @item -B @var{bitclock}
-Specify the bit clock period for the JTAG interface or the ISP clock (JTAG ICE only).
-The value is a floating-point number in microseconds.
-Alternatively, the value might be suffixed with "Hz", "kHz", or "MHz",
-in order to specify the bit clock frequency, rather than a period.
-The default value of the JTAG ICE results in about 1 microsecond bit
-clock period, suitable for target MCUs running at 4 MHz clock and
-above.
-Unlike certain parameters in the STK500, the JTAG ICE resets all its
-parameters to default values when the programming software signs
-off from the ICE, so for MCUs running at lower clock speeds, this
-parameter must be specified on the command-line.
-It can also be set in the configuration file by using the 'default_bitclock'
-keyword.
+Specify the bit clock period for the JTAG, PDI, TPI, UPDI, or ISP
+interface. The value is a floating-point number in microseconds.
+Alternatively, the value might be suffixed with "Hz", "kHz" or
+"MHz" in order to specify the bit clock frequency rather than a
+period. Some programmers default their bit clock value to a 1
+microsecond bit clock period, suitable for target MCUs running at 4
+MHz clock and above. Slower MCUs need a correspondingly higher bit
+clock period. Some programmers reset their bit clock value to the
+default value when the programming software signs off, whilst
+others store the last used bit clock value. It is recommended to
+always specify the bit clock if read/write speed is important.  You
+can use the 'default_bitclock' keyword in your
+@code{~/.config/avrdude/avrdude.rc} or @code{~/.avrduderc}
+configuration file to assign a default value to keep from having to
+specify this option on every invocation.
 
 @item -c @var{programmer-id}
 Specify the programmer to be used.  AVRDUDE knows about several common

src/main.c

@@ -167,14 +167,14 @@ static void usage(void)
     "Options:\n"
     "  -p <partno>                Specify AVR device\n"
     "  -b <baudrate>              Override RS-232 baud rate\n"
-    "  -B <bitclock>              Specify JTAG/STK500v2 bit clock period (us)\n"
+    "  -B <bitclock>              Specify bit clock period (us)\n"
     "  -C <config-file>           Specify location of configuration file\n"
     "  -c <programmer>            Specify programmer type\n"
     "  -A                         Disable trailing-0xff removal from file and AVR read\n"
     "  -D                         Disable auto erase for flash memory; implies -A\n"
     "  -i <delay>                 ISP Clock Delay [in microseconds]\n"
     "  -P <port>                  Specify connection port\n"
-    "  -F                         Override invalid signature check\n"
+    "  -F                         Override invalid signature or initialisation check\n"
     "  -e                         Perform a chip erase\n"
     "  -O                         Perform RC oscillator calibration (see AVR053)\n"
     "  -U <memtype>:r|w|v:<filename>[:format]\n"