Change BOARD_SPEED to BOARD_CLOCK setting and extend to menu.clock and menu.speed.

This is needed to specify CPU speed and fuses for boards.txt files that use this format:
"{board_tag}.menu.clock.{board_clock}.build.f_cpu"
"{board_tag}.menu.clock.{board_clock}.bootloader.low_fuses"
"{board_tag}.menu.clock.{board_clock}.bootloader.high_fuses"
"{board_tag}.menu.clock.{board_clock}.bootloader.extended_fuses"
For example ATtiny processors.

It also works for speed-only settings like the Watterott ATmega328PB library: https://github.com/watterott/ATmega328PB-Testing
"{board_tag}.menu.speed.{board_clock}.build.f_cpu"

1 files changed, 14 insertions, 5 deletions

diff --git a/arduino-mk-vars.md b/arduino-mk-vars.md
index f08b0a2..3ee05d0 100644
--- a/arduino-mk-vars.md
+++ b/arduino-mk-vars.md
@@ -344,21 +344,30 @@ BOARD_SUB=atmega168
 
 ----
 
-### BOARD_SPEED
+### BOARD_CLOCK
 
 **Description:**
 
-Allow selection of f_cpu value specified in `boards.txt` as `board_tag.menu.speed.board_speed`.
+Allow selection of f_cpu and fuses specified in `boards.txt` as `{BOARD_TAG}.menu.clock.{BOARD_CLOCK}`.
+This works for microprocessor board definitions like ATtiny that specify not only the clock speed but fuse settings as clock overrides.
+
+It also works for f_cpu values specified in `boards.txt` as `{BOARD_TAG}.menu.speed.{BOARD_CLOCK}`.
 For example, the Watterott ATmega328PB library [https://github.com/watterott/ATmega328PB-Testing](https://github.com/watterott/ATmega328PB-Testing).
 
 **Example:**
 
 ```Makefile
-# Select 20MHz clock
-BOARD_SPEED=20mhz
+# Select external 16 MHz clock
+BOARD_CLOCK=external16
+```
+
+**Example:**
+```Makefile
+# Select 20MHz speed
+BOARD_CLOCK=20mhz
 ```
 
-**Requirement:** *Optional to override main board f_cpu setting*
+**Requirement:** *Optional to override main board f_cpu and/or fuse settings.*
 
 ----