ports: Implement simple write polling for stdout.

This is a best-effort implementation of write polling.  It's difficult to
do correctly because if there are multiple output streams (eg UART and USB
CDC) then some may not be writeable while others are.  A full solution
should also have a return value from mp_hal_stdout_tx_strn(), returning the
number of bytes written to the stream(s).  That's also hard to define.

The renesas-ra and stm32 ports already implement a similar best-effort
mechanism for write polling.

Fixes issue #11026.

Signed-off-by: Damien George <damien@micropython.org>

10 files changed, 39 insertions, 0 deletions

diff --git a/ports/esp32/mphalport.c b/ports/esp32/mphalport.c
index 2aaeb9755..b187b422d 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 3cb480733..219e61484 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 2730b9a85..beb471ab8 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 3020f1af6..320657370 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 16d69fff6..e33a42548 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 9405cb2e3..a2eec7fce 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 48e8af87d..b2c80ba1b 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 510d486d9..f56c2bda1 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 d7511e61f..3dc6b70a8 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 93103319b..62a826517 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;
 }