Add sem_drain_and_wait_timeout and time_to_ticks to lispBM.

The new `sem_drain_and_wait_timeout` effectively achieves binary
semaphore semantics without relying on `ch_binary_semaphore`.

`time_to_ticks` is necessary to pass the correct timeout values to
`sem_wait_to` and `sem_drain_and_wait_timeout`

lispBM/c_libs/vesc_c_if.h

@@ -650,12 +650,16 @@ typedef struct {
 	const float* (*foc_get_audio_sample_table)(int channel);
 	bool (*foc_play_audio_samples)(const int8_t *samples, int num_samp, float f_samp, float voltage);
 
-	// Semaphore
+	// Semaphores
 	lib_semaphore (*sem_create)(void); // Use VESC_IF->free on the semaphore when done with it
 	void (*sem_wait)(lib_semaphore);
 	void (*sem_signal)(lib_semaphore);
 	bool (*sem_wait_to)(lib_semaphore, systime_t); // Returns false on timeout
 	void (*sem_reset)(lib_semaphore);
+	int32_t (*sem_drain_and_wait_timeout)(lib_semaphore, systime_t);
+
+	// Os continued
+	systime_t (*time_to_ticks)(uint32_t seconds, uint32_t millis, uint32_t micros);
 } vesc_c_if;
 
 typedef struct {

lispBM/lispif_c_lib.c

@@ -655,6 +655,33 @@ static void lib_sem_reset(lib_semaphore s) {
 	chSemReset((semaphore_t*)s, 0);
 }
 
+// Guaranteed to block. First drains the semaphore to 0 if its counter is positive and
+// then waits on it with given timeout(special values TIME_IMMEDIATE and TIME_INFINITE are honored).
+// Returns MSG_RESET or MSG_TIMEOUT if that was the result of the wait operations.
+// Otherwise returns a non-negative number of overruns, i.e. the number by which the semaphore
+// had to be decreased before the wait operation.
+//
+// Useful for implementing binary-semaphore like semantics where it's important to ignore
+// semaphore overruns.
+static int32_t lib_sem_drain_and_wait_timeout(lib_semaphore sem, systime_t timeout) {
+	chSysLock();
+	const cnt_t sem_counter =  chSemGetCounterI((semaphore_t*)sem);
+	// setCounter isn't exposed and I don't want to manually manipulate the internal counter
+	for (cnt_t i = 0; i < sem_counter; i++) {
+		chSemFastWaitI((semaphore_t*)sem);
+	}
+	const msg_t wait_result = chSemWaitTimeoutS((semaphore_t*)sem, timeout);
+	chSysUnlock();
+	if (wait_result < 0) { // MSG_RESET and MSG_TIMEOUT are negative
+		return wait_result;
+	}
+	return sem_counter < 0 ? 0 : sem_counter;
+}
+
+static systime_t lib_time_to_ticks(uint32_t seconds, uint32_t millis, uint32_t micros) {
+	return S2ST(seconds) + MS2ST(millis) + US2ST(micros);
+}
+
 static remote_state lib_get_remote_state(void) {
 	remote_state res;
 	res.js_x = app_nunchuk_get_decoded_x();
@@ -1022,6 +1049,10 @@ lbm_value ext_load_native_lib(lbm_value *args, lbm_uint argn) {
 		cif.cif.sem_signal = lib_sem_signal;
 		cif.cif.sem_wait_to = lib_sem_wait_to;
 		cif.cif.sem_reset = lib_sem_reset;
+		cif.cif.sem_drain_and_wait_timeout = lib_sem_drain_and_wait_timeout;
+
+		// OS continued
+		cif.cif.time_to_ticks = lib_time_to_ticks;
 
 		lib_init_done = true;
 	}