runtime: move timeUnit to a single place

The timeUnit is now the same type everywhere. Move it to a single place
and add some documentation to it.

Author: aykevl

src/runtime/runtime.go

@@ -8,6 +8,17 @@ import (
 
 const Compiler = "tinygo"
 
+// Unit for the 'ticks' and 'sleepTicks' functions.
+//
+// This is the native time unit for the given system. One timeUnit tick might be
+// 1ns or 100ns on a desktop system, or 1/32768s on baremetal systems with a
+// low-power RTC. Many other tick durations are possible.
+//
+// Conversion from time units to nanoseconds and back is done using
+// ticksToNanoseconds and nanosecondsToTicks, which need to be implemented for
+// each system as needed.
+type timeUnit int64
+
 // The compiler will fill this with calls to the initialization function of each
 // package.
 func initAll()

src/runtime/runtime_arm7tdmi.go

@@ -7,8 +7,6 @@ import (
 	"unsafe"
 )
 
-type timeUnit int64
-
 func putchar(c byte) {
 	// dummy, TODO
 }

src/runtime/runtime_atsamd21.go

@@ -12,8 +12,6 @@ import (
 	"unsafe"
 )
 
-type timeUnit int64
-
 //export Reset_Handler
 func main() {
 	preinit()

src/runtime/runtime_atsamd51.go

@@ -11,8 +11,6 @@ import (
 	"runtime/volatile"
 )
 
-type timeUnit int64
-
 //export Reset_Handler
 func main() {
 	arm.SCB.CPACR.Set(0) // disable FPU if it is enabled

src/runtime/runtime_avr.go

@@ -12,9 +12,6 @@ import (
 
 const BOARD = "arduino"
 
-// timeUnit in nanoseconds
-type timeUnit int64
-
 // Watchdog timer periods. These can be off by a large margin (hence the jump
 // between 64ms and 125ms which is not an exact double), so don't rely on this
 // for accurate time keeping.

src/runtime/runtime_avrtiny.go

@@ -22,8 +22,6 @@ import (
 	"runtime/volatile"
 )
 
-type timeUnit int64
-
 //export main
 func main() {
 	// Initialize RTC.

src/runtime/runtime_cortexm_qemu.go

@@ -11,8 +11,6 @@ import (
 	"unsafe"
 )
 
-type timeUnit int64
-
 var timestamp timeUnit
 
 //export Reset_Handler

src/runtime/runtime_esp32xx.go

@@ -8,8 +8,6 @@ import (
 	"unsafe"
 )
 
-type timeUnit int64
-
 // Initialize .bss: zero-initialized global variables.
 // The .data section has already been loaded by the ROM bootloader.
 func clearbss() {

src/runtime/runtime_esp8266.go

@@ -9,8 +9,6 @@ import (
 	"unsafe"
 )
 
-type timeUnit int64
-
 var currentTime timeUnit = 0
 
 func putchar(c byte) {

src/runtime/runtime_fe310.go

@@ -14,8 +14,6 @@ import (
 	"runtime/volatile"
 )
 
-type timeUnit int64
-
 //export main
 func main() {
 	// Zero the PLIC enable bits on startup: they are not zeroed at reset.