fixup! stdio_semihosting: port to new interface

sys/stdio_semihosting/stdio_semihosting.c

@@ -133,6 +133,10 @@ static size_t _semihosting_write(const uint8_t *buffer, size_t len)
 
 static ssize_t _semihosting_read(uint8_t *buffer, size_t len)
 {
+    if (!_semihosting_connected()) {
+        return 0;
+    }
+
     uint32_t args[3] = {
         STDIO_SEMIHOSTING_F_STDIN,
         (uint32_t)buffer,
@@ -156,7 +160,7 @@ static bool _read_cb(void *arg)
 
 static bool _init_done;
 static void _init(void) {
-    if (!STDIO_SEMIHOSTING_RX) {
+    if (!STDIO_SEMIHOSTING_RX || !IS_USED(MODULE_STDIO_DISPATCH)) {
         return;
     }
 
@@ -183,8 +187,36 @@ static ssize_t _write(const void* buffer, size_t len)
     if (!_semihosting_connected()) {
         return len;
     }
+    if (STDIO_SEMIHOSTING_RX && IS_USED(MODULE_STDIO_DISPATCH)
+        && !_init_done) {
+        _init();
+    }
+
     size_t remaining = _semihosting_write(buffer, len);
     return len - remaining;
 }
 
+#ifndef MODULE_STDIO_DISPATCH
+ssize_t stdio_read(void* buffer, size_t count)
+{
+    if (!STDIO_SEMIHOSTING_RX) {
+        return -ENOTSUP;
+    }
+
+    uint32_t last_wakeup = ztimer_now(ZTIMER_MSEC);
+    ssize_t bytes_read = _semihosting_read(buffer, count);
+    while (bytes_read == 0) {
+        ztimer_periodic_wakeup(ZTIMER_MSEC, &last_wakeup,
+                               STDIO_SEMIHOSTING_POLL_RATE_MS);
+        bytes_read = _semihosting_read(buffer, count);
+    }
+    return bytes_read;
+}
+
+int stdio_available(void)
+{
+    return -ENOTSUP;
+}
+#endif
+
 STDIO_PROVIDER(STDIO_SEMIHOSTING, _init, _detach, _write)