fixup! fixup! fixup! fixup! doc/guides: Add timer information to Porting Boards

Author: crasbe

doc/guides/advanced_tutorials/porting_boards.md

@@ -237,12 +237,14 @@ pip install --upgrade riotgen
 
 ### Timer Width
 
-Some resource constrained or low-power microcontrollers only have 16-bit
-wide timer registers available. By default `ztimer` assumes a timer width of
-32-bits, so you have to explicitly specify the maximum value the timer register
-can hold.
+The `ztimer` driver assumes a timer register bit-width of 32-bits by default.
+If your microcontroller has a smaller  timer register (e.g. 16-bits), you have
+to explicitly specify the maximum value the timer register can hold with the
+`TIMER_0_MAX_VALUE` define.
 This is the same value that is put in the `max` field of the `timer_config`
 structure.
+Typical values are `0x0000FFFFUL` for 16-bit wide timers, `0x00FFFFFFUL` for
+24-bit wide timers and `0xFFFFFFFFUL` for 32-bit wide timers.
 
 ```c
 static const timer_conf_t timer_config[] = {