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//go:build scheduler.tasks && esp8266
// +build scheduler.tasks,esp8266
package task
// Stack switch implementation for the ESP8266, which does not use the windowed
// ABI of Xtensa. Registers are assigned as follows:
// a0: return address (link register)
// a1: stack pointer (must be 16-byte aligned)
// a2-a7: incoming arguments
// a8: static chain (unused)
// a12-a15: callee-saved
// a15: stack frame pointer (optional, unused)
// Sources:
// http://cholla.mmto.org/esp8266/xtensa.html
// https://0x04.net/~mwk/doc/xtensa.pdf
import "unsafe"
var systemStack uintptr
// calleeSavedRegs is the list of registers that must be saved and restored when
// switching between tasks. Also see task_stack_esp8266.S that relies on the
// exact layout of this struct.
type calleeSavedRegs struct {
a12 uintptr
a13 uintptr
a14 uintptr
a15 uintptr
pc uintptr // also link register or r0
}
// archInit runs architecture-specific setup for the goroutine startup.
func (s *state) archInit(r *calleeSavedRegs, fn uintptr, args unsafe.Pointer) {
// Store the initial sp for the startTask function (implemented in assembly).
s.sp = uintptr(unsafe.Pointer(r))
// Initialize the registers.
// These will be popped off of the stack on the first resume of the goroutine.
// Start the function at tinygo_startTask (defined in
// src/internal/task/task_stack_esp8266.S).
// This assembly code calls a function (passed in a12) with a single argument
// (passed in a13). After the function returns, it calls Pause().
r.pc = uintptr(unsafe.Pointer(&startTask))
// Pass the function to call in a12.
// This function is a compiler-generated wrapper which loads arguments out of a struct pointer.
// See createGoroutineStartWrapper (defined in compiler/goroutine.go) for more information.
r.a12 = fn
// Pass the pointer to the arguments struct in a13.
r.a13 = uintptr(args)
}
func (s *state) resume() {
swapTask(s.sp, &systemStack)
}
func (s *state) pause() {
newStack := systemStack
systemStack = 0
swapTask(newStack, &s.sp)
}
// SystemStack returns the system stack pointer when called from a task stack.
// When called from the system stack, it returns 0.
func SystemStack() uintptr {
return systemStack
}
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