timerfns
const struct timerfns *timerfns;
timerattach(device_t dev, const struct timerfns *fns)
if (timerfns != NULL)
timerfns = fns;
if (timerfns == NULL)
(*timerfns->tf_init)(timerdev);
void timerattach(device_t, const struct timerfns *);
struct timerfns timerfns_isa = {
struct timerfns timerfns_jazzio = {