diff --git a/bricks/_common_stm32/mphalport.c b/bricks/_common_stm32/mphalport.c
index d2a2fc30c..ae54727a0 100644
--- a/bricks/_common_stm32/mphalport.c
+++ b/bricks/_common_stm32/mphalport.c
@@ -88,13 +88,17 @@ int mp_hal_stdin_rx_chr(void) {
 }
 
 // Send string of given length
-void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, size_t len) {
+    size_t org_len = len;
+
     while (len--) {
         while (!(USART6->SR & USART_SR_TXE)) {
             MICROPY_VM_HOOK_LOOP
         }
         USART6->DR = *str++;
     }
+
+    return org_len;
 }
 
 void mp_hal_stdout_tx_flush(void) {
@@ -127,7 +131,9 @@ int mp_hal_stdin_rx_chr(void) {
 }
 
 // Send string of given length
-void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, size_t len) {
+    size_t org_len = len;
+
     while (len) {
         uint32_t size = len;
         pbio_error_t err = pbsys_bluetooth_tx((const uint8_t *)str, &size);
@@ -141,11 +147,13 @@ void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
         if (err != PBIO_ERROR_AGAIN) {
             // Ignoring error for now. This means stdout lost if Bluetooth is
             // disconnected.
-            return;
+            return org_len - len;
         }
 
         MICROPY_EVENT_POLL_HOOK
     }
+
+    return org_len;
 }
 
 void mp_hal_stdout_tx_flush(void) {
diff --git a/bricks/ev3dev/ev3dev_mphal.c b/bricks/ev3dev/ev3dev_mphal.c
index 6dd1aa25a..e4ac74983 100644
--- a/bricks/ev3dev/ev3dev_mphal.c
+++ b/bricks/ev3dev/ev3dev_mphal.c
@@ -109,11 +109,26 @@ int mp_hal_stdin_rx_chr(void) {
     return c;
 }
 
-void mp_hal_stdout_tx_strn(const char *str, size_t len) {
-    MP_THREAD_GIL_EXIT();
-    int ret = write(STDOUT_FILENO, str, len);
-    MP_THREAD_GIL_ENTER();
-    (void)ret; // to suppress compiler warning
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, size_t len) {
+    size_t remaining = len;
+    while (remaining > 0) {
+        MP_THREAD_GIL_EXIT();
+        ssize_t ret = write(STDOUT_FILENO, str, remaining);
+        MP_THREAD_GIL_ENTER();
+        if (ret < 0) {
+            if (errno == EINTR) {
+                continue;
+            }
+            return len - remaining;
+        }
+        /* Defensive check: POSIX guarantees ret <= remaining, but guard against non-compliant implementations. */
+        if ((size_t)ret > remaining) {
+            return len;
+        }
+        str += ret;
+        remaining -= (size_t)ret;
+    }
+    return len;
 }
 
 // cooked is same as uncooked because the terminal does some postprocessing
diff --git a/bricks/ev3rt/mphalport.c b/bricks/ev3rt/mphalport.c
index 7f1dfab2d..14602fe92 100644
--- a/bricks/ev3rt/mphalport.c
+++ b/bricks/ev3rt/mphalport.c
@@ -75,11 +75,14 @@ int mp_hal_stdin_rx_chr(void) {
 }
 
 // Send string of given length
-void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, size_t len) {
     uint32_t in_waiting;
     if (bluetooth_is_connected(&in_waiting)) {
         serial_wri_dat(EV3_SERIAL_BT, str, len);
+        return len;
     }
+
+    return 0;
 }
 
 void mp_hal_stdout_tx_flush(void) {
diff --git a/bricks/nxt/mphalport.c b/bricks/nxt/mphalport.c
index dafb13453..369620cf8 100644
--- a/bricks/nxt/mphalport.c
+++ b/bricks/nxt/mphalport.c
@@ -85,17 +85,20 @@ int mp_hal_stdin_rx_chr(void) {
 }
 
 // Send string of given length
-void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, size_t len) {
 
     // Nothing to do if disconnected or empty data
     if (!nx_bt_stream_opened() || len == 0) {
-        return;
+        return 0;
     }
 
+    size_t org_len = len;
     nx_bt_stream_write((uint8_t *)str, len);
     while (!nx_bt_stream_data_written()) {
         MICROPY_EVENT_POLL_HOOK;
     }
+
+    return org_len;
 }
 
 void mp_hal_stdout_tx_flush(void) {
diff --git a/bricks/primehub_spike-rt/mphalport.c b/bricks/primehub_spike-rt/mphalport.c
index 5f22f97d6..26104a81f 100644
--- a/bricks/primehub_spike-rt/mphalport.c
+++ b/bricks/primehub_spike-rt/mphalport.c
@@ -58,14 +58,14 @@ int mp_hal_stdin_rx_chr(void) {
 }
 
 // Send string of given length
-//void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
 mp_uint_t mp_hal_stdout_tx_strn(const char *str, size_t len) {
+    size_t org_len = len;
     extern void tPutLogTarget_ePutLog_putChar(char c);
     while (len--) {
         tPutLogTarget_ePutLog_putChar(*str++);
     }
     // serial_wri_dat(TASK_PORTID, str, len)
-    return 0;
+    return org_len;
 }
 
 #else // !PYBRICKS_HUB_DEBUG
@@ -94,7 +94,9 @@ int mp_hal_stdin_rx_chr(void) {
 }
 
 // Send string of given length
-void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+mp_uint_t mp_hal_stdout_tx_strn(const char *str, size_t len) {
+    size_t org_len = len;
+
     while (len) {
         uint32_t size = len;
         pbio_error_t err = pbsys_bluetooth_tx((const uint8_t *)str, &size);
@@ -108,11 +110,13 @@ void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
         if (err != PBIO_ERROR_AGAIN) {
             // Ignoring error for now. This means stdout lost if Bluetooth is
             // disconnected.
-            return;
+            return org_len - len;
         }
 
         MICROPY_EVENT_POLL_HOOK
     }
+
+    return org_len;
 }
 
 #endif // PYBRICKS_HUB_DEBUG