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Ayke van Laethem
3a2188fc7b
This type can be used to jump back to a previous position in a program
from inside an interrupt. This is useful for baremetal systems that
implement wfi but not wfe, and therefore have no easy (race-free) way to
wait until a flag gets changed inside an interrupt. This is an issue on
RISC-V, where this is racy (the interrupt might happen after the check
but before the wfi instruction):
configureInterrupt()
for flag.Load() != 0 {
riscv.Asm("wfi")
}
63 lines
1.5 KiB
Go
63 lines
1.5 KiB
Go
package interrupt
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// A checkpoint is a setjmp like buffer, that can be used as a flag for
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// interrupts.
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//
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// It can be used as follows:
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//
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// // global var
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// var c Checkpoint
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//
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// // to set up the checkpoint and wait for it
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// if c.Save() {
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// setupInterrupt()
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// for {
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// waitForInterrupt()
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// }
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// }
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//
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// // Inside the interrupt handler:
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// if c.Saved() {
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// c.Jump()
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// }
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type Checkpoint struct {
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jumpSP uintptr
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jumpPC uintptr
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}
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// Save the execution state in the given checkpoint, overwriting a previous
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// saved checkpoint.
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//
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// This function returns twice: once the normal way after saving (returning
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// true) and once after jumping (returning false).
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//
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// This function is a compiler intrinsic, it is not implemented in Go.
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func (c *Checkpoint) Save() bool
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// Returns whether a jump point was saved (and not erased due to a jump).
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func (c *Checkpoint) Saved() bool {
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return c.jumpPC != 0
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}
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// Jump to the point where the execution state was saved, and erase the saved
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// jump point. This must *only* be called from inside an interrupt.
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//
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// This method does not return in the conventional way, it resumes execution at
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// the last point a checkpoint was saved.
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func (c *Checkpoint) Jump() {
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if !c.Saved() {
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panic("runtime/interrupt: no checkpoint was saved")
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}
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jumpPC := c.jumpPC
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jumpSP := c.jumpSP
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c.jumpPC = 0
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c.jumpSP = 0
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if jumpPC == 0 {
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panic("jumping to 0")
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}
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checkpointJump(jumpSP, jumpPC)
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}
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//export tinygo_checkpointJump
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func checkpointJump(jumpSP, jumpPC uintptr)
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