diff --git a/ports/esp32/mphalport.c b/ports/esp32/mphalport.c
index 2aaeb9755f..b187b422d5 100644
--- a/ports/esp32/mphalport.c
+++ b/ports/esp32/mphalport.c
@@ -88,6 +88,9 @@ uintptr_t mp_hal_stdio_poll(uintptr_t poll_flags) {
     if ((poll_flags & MP_STREAM_POLL_RD) && stdin_ringbuf.iget != stdin_ringbuf.iput) {
         ret |= MP_STREAM_POLL_RD;
     }
+    if (poll_flags & MP_STREAM_POLL_WR) {
+        ret |= MP_STREAM_POLL_WR;
+    }
     return ret;
 }
 
diff --git a/ports/esp8266/esp_mphal.c b/ports/esp8266/esp_mphal.c
index 3cb4807333..219e614841 100644
--- a/ports/esp8266/esp_mphal.c
+++ b/ports/esp8266/esp_mphal.c
@@ -62,6 +62,9 @@ uintptr_t mp_hal_stdio_poll(uintptr_t poll_flags) {
     if ((poll_flags & MP_STREAM_POLL_RD) && stdin_ringbuf.iget != stdin_ringbuf.iput) {
         ret |= MP_STREAM_POLL_RD;
     }
+    if (poll_flags & MP_STREAM_POLL_WR) {
+        ret |= mp_uos_dupterm_poll(poll_flags);
+    }
     return ret;
 }
 
diff --git a/ports/mimxrt/mphalport.c b/ports/mimxrt/mphalport.c
index 2730b9a855..beb471ab80 100644
--- a/ports/mimxrt/mphalport.c
+++ b/ports/mimxrt/mphalport.c
@@ -86,6 +86,9 @@ uintptr_t mp_hal_stdio_poll(uintptr_t poll_flags) {
     if ((poll_flags & MP_STREAM_POLL_RD) && ringbuf_peek(&stdin_ringbuf) != -1) {
         ret |= MP_STREAM_POLL_RD;
     }
+    if ((poll_flags & MP_STREAM_POLL_WR) && tud_cdc_connected() && tud_cdc_write_available() > 0) {
+        ret |= MP_STREAM_POLL_WR;
+    }
     #if MICROPY_PY_OS_DUPTERM
     ret |= mp_uos_dupterm_poll(poll_flags);
     #endif
diff --git a/ports/nrf/drivers/bluetooth/ble_uart.c b/ports/nrf/drivers/bluetooth/ble_uart.c
index 3020f1af62..3206573703 100644
--- a/ports/nrf/drivers/bluetooth/ble_uart.c
+++ b/ports/nrf/drivers/bluetooth/ble_uart.c
@@ -164,6 +164,9 @@ uintptr_t mp_hal_stdio_poll(uintptr_t poll_flags) {
         && !isBufferEmpty(mp_rx_ring_buffer)) {
         ret |= MP_STREAM_POLL_RD;
     }
+    if ((poll_flags & MP_STREAM_POLL_WR) && ble_uart_enabled()) {
+        ret |= MP_STREAM_POLL_WR;
+    }
     return ret;
 }
 #endif
diff --git a/ports/nrf/drivers/usb/usb_cdc.c b/ports/nrf/drivers/usb/usb_cdc.c
index 16d69fff66..e33a425482 100644
--- a/ports/nrf/drivers/usb/usb_cdc.c
+++ b/ports/nrf/drivers/usb/usb_cdc.c
@@ -213,6 +213,9 @@ uintptr_t mp_hal_stdio_poll(uintptr_t poll_flags) {
             ret |= MP_STREAM_POLL_RD;
         }
     }
+    if (poll_flags & MP_STREAM_POLL_WR) {
+        ret |= MP_STREAM_POLL_WR;
+    }
     return ret;
 }
 
diff --git a/ports/nrf/mphalport.c b/ports/nrf/mphalport.c
index 9405cb2e3a..a2eec7fceb 100644
--- a/ports/nrf/mphalport.c
+++ b/ports/nrf/mphalport.c
@@ -179,6 +179,9 @@ uintptr_t mp_hal_stdio_poll(uintptr_t poll_flags) {
         && uart_rx_any(MP_STATE_PORT(board_stdio_uart))) {
         ret |= MP_STREAM_POLL_RD;
     }
+    if ((poll_flags & MP_STREAM_POLL_WR) && MP_STATE_PORT(board_stdio_uart) != NULL) {
+        ret |= MP_STREAM_POLL_WR;
+    }
     return ret;
 }
 
diff --git a/ports/pic16bit/pic16bit_mphal.c b/ports/pic16bit/pic16bit_mphal.c
index 48e8af87de..b2c80ba1be 100644
--- a/ports/pic16bit/pic16bit_mphal.c
+++ b/ports/pic16bit/pic16bit_mphal.c
@@ -57,6 +57,9 @@ uintptr_t mp_hal_stdio_poll(uintptr_t poll_flags) {
     if ((poll_flags & MP_STREAM_POLL_RD) && uart_rx_any()) {
         ret |= MP_STREAM_POLL_RD;
     }
+    if (poll_flags & MP_STREAM_POLL_WR) {
+        ret |= MP_STREAM_POLL_WR;
+    }
     return ret;
 }
 
diff --git a/ports/rp2/mphalport.c b/ports/rp2/mphalport.c
index 510d486d96..f56c2bda13 100644
--- a/ports/rp2/mphalport.c
+++ b/ports/rp2/mphalport.c
@@ -98,6 +98,15 @@ uintptr_t mp_hal_stdio_poll(uintptr_t poll_flags) {
     if ((poll_flags & MP_STREAM_POLL_RD) && ringbuf_peek(&stdin_ringbuf) != -1) {
         ret |= MP_STREAM_POLL_RD;
     }
+    if (poll_flags & MP_STREAM_POLL_WR) {
+        #if MICROPY_HW_ENABLE_UART_REPL
+        ret |= MP_STREAM_POLL_WR;
+        #else
+        if (tud_cdc_connected() && tud_cdc_write_available() > 0) {
+            ret |= MP_STREAM_POLL_WR;
+        }
+        #endif
+    }
     #endif
     #if MICROPY_PY_OS_DUPTERM
     ret |= mp_uos_dupterm_poll(poll_flags);
diff --git a/ports/samd/mphalport.c b/ports/samd/mphalport.c
index d7511e61fb..3dc6b70a8d 100644
--- a/ports/samd/mphalport.c
+++ b/ports/samd/mphalport.c
@@ -162,6 +162,10 @@ uintptr_t mp_hal_stdio_poll(uintptr_t poll_flags) {
         ret |= MP_STREAM_POLL_RD;
     }
 
+    if ((poll_flags & MP_STREAM_POLL_WR) && tud_cdc_connected() && tud_cdc_write_available() > 0) {
+        ret |= MP_STREAM_POLL_WR;
+    }
+
     #if MICROPY_PY_OS_DUPTERM
     ret |= mp_uos_dupterm_poll(poll_flags);
     #endif
diff --git a/ports/teensy/teensy_hal.c b/ports/teensy/teensy_hal.c
index 93103319b5..62a8265177 100644
--- a/ports/teensy/teensy_hal.c
+++ b/ports/teensy/teensy_hal.c
@@ -32,6 +32,11 @@ uintptr_t mp_hal_stdio_poll(uintptr_t poll_flags) {
             ret |= MP_STREAM_POLL_RD;
         }
     }
+    if (poll_flags & MP_STREAM_POLL_WR) {
+        if (MP_STATE_PORT(pyb_stdio_uart) != NULL || usb_vcp_is_enabled()) {
+            ret |= MP_STREAM_POLL_WR;
+        }
+    }
     return ret;
 }