libtock: add yield-waitfor function

Author: ppannuto

libtock/tock.c

@@ -184,6 +184,25 @@ int yield_no_wait(void) {
   return (int)result;
 }
 
+yield_waitfor_return_t yield_wait_for(uint32_t driver, uint32_t subscribe) {
+  register uint32_t waitfor __asm__ ("r0") = 2; // yield-waitfor
+  register uint32_t r1 __asm__ ("r1")      = driver;
+  register uint32_t r2 __asm__ ("r2")      = subscribe;
+  register int rv0 __asm__ ("r0");
+  register int rv1 __asm__ ("r1");
+  register int rv2 __asm__ ("r2");
+
+  __asm__ volatile (
+    "svc 0       \n"
+    : "=r" (rv0), "=r" (rv1), "=r" (rv2)
+    : "r" (waitfor), "r" (r1), "r" (r2)
+    : "memory"
+    );
+  yield_waitfor_return_t rv = {rv0, rv1, rv2};
+  return rv;
+}
+
+
 void tock_exit(uint32_t completion_code) {
   register uint32_t r0 __asm__ ("r0") = 0; // Terminate
   register uint32_t r1 __asm__ ("r1") = completion_code;
@@ -400,6 +419,23 @@ int yield_no_wait(void) {
   return (int)result;
 }
 
+yield_waitfor_return_t yield_wait_for(uint32_t driver, uint32_t subscribe) {
+  register uint32_t waitfor __asm__ ("a0") = 2; // yield-waitfor
+  register uint32_t a1 __asm__ ("a1")      = driver;
+  register uint32_t a2 __asm__ ("a2")      = subscribe;
+  register uint32_t a4 __asm__ ("a4")      = 0; // Yield
+  register int rv0 __asm__ ("a0");
+  register int rv1 __asm__ ("a1");
+  register int rv2 __asm__ ("a2");
+  __asm__ volatile (
+    "ecall\n"
+    : "=r" (rv0), "=r" (rv1), "=r" (rv2)
+    : "r" (waitfor), "r" (a1), "r" (a2), "r" (a4)
+    : "memory");
+  yield_waitfor_return_t rv = {rv0, rv1, rv2};
+  return rv;
+}
+
 
 void tock_restart(uint32_t completion_code) {
   register uint32_t a0  __asm__ ("a0") = 1; // exit-restart

libtock/tock.h

@@ -127,6 +127,18 @@ typedef struct {
   uint32_t data;
 } memop_return_t;
 
+// Return structure for a Yield-WaitFor syscall. The return value are the
+// arguments that would have been passed to the upcall the the Yield-WaitFor was
+// waiting on.
+typedef struct {
+  // Upcall argument 1.
+  uint32_t data0;
+  // Upcall argument 2.
+  uint32_t data1;
+  // Upcall argument 3.
+  uint32_t data2;
+} yield_waitfor_return_t;
+
 ////////////////////////////////////////////////////////////////////////////////
 ///
 /// HELPER FUNCTIONS
@@ -177,6 +189,7 @@ int tock_allow_userspace_r_return_to_returncode(allow_userspace_r_return_t);
 void yield(void);
 void yield_for(bool*);
 int yield_no_wait(void);
+yield_waitfor_return_t yield_wait_for(uint32_t driver, uint32_t subscribe);
 
 void tock_exit(uint32_t completion_code) __attribute__ ((noreturn));
 void tock_restart(uint32_t completion_code) __attribute__ ((noreturn));