shared/tinyusb: Buffer startup CDC data to send to host on connection.

At startup, buffer initial stdout / MicroyPthon banner so that it can be
sent to the host on initial connection of the USB serial port.  This
buffering also works for when the CDC becomes disconnected and the device
is still printing to stdout, and when CDC is reconnected the most recent
part of stdout (depending on how big the internal USB FIFO is) is flushed
to the host.

This change is most obvious when you've first plugged in a MicroPython
device (or hit reset), when it's a board that uses USB (CDC) serial in the
chip itself for the REPL interface.  This doesn't apply to UART going via a
separate USB-serial chip.

The stm32 port already has this buffering behaviour (it doesn't use
TinyUSB) and this commit extends such behaviour to rp2, mimxrt, samd and
renesas-ra ports, which do use TinyUSB.

Signed-off-by: Andrew Leech <[email protected]>

Author: pi-anl

ports/mimxrt/tusb_config.h

@@ -32,5 +32,6 @@
 #define CFG_TUD_CDC             (1)
 #define CFG_TUD_CDC_RX_BUFSIZE  (512)
 #define CFG_TUD_CDC_TX_BUFSIZE  (512)
+#define CFG_TUD_CDC_PERSISTENT_TX_BUFF (1)
 
 #endif // MICROPY_INCLUDED_MIMXRT_TUSB_CONFIG_H

shared/tinyusb/mp_usbd_cdc.c

@@ -35,6 +35,7 @@
 #if MICROPY_HW_USB_CDC && MICROPY_HW_ENABLE_USBDEV && !MICROPY_EXCLUDE_SHARED_TINYUSB_USBD_CDC
 
 static uint8_t cdc_itf_pending; // keep track of cdc interfaces which need attention to poll
+static int8_t cdc_connected_flush_delay = 0;
 
 uintptr_t mp_usbd_cdc_poll_interfaces(uintptr_t poll_flags) {
     uintptr_t ret = 0;
@@ -58,7 +59,9 @@ uintptr_t mp_usbd_cdc_poll_interfaces(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) {
+    if ((poll_flags & MP_STREAM_POLL_WR) &&
+        (!tud_cdc_connected() || (tud_cdc_connected() && tud_cdc_write_available() > 0))) {
+        // Always allow write when not connected, fifo will retain latest.
         // When connected operate as blocking, only allow if space is available.
         ret |= MP_STREAM_POLL_WR;
     }
@@ -93,42 +96,55 @@ void tud_cdc_rx_cb(uint8_t itf) {
 
 mp_uint_t mp_usbd_cdc_tx_strn(const char *str, mp_uint_t len) {
     size_t i = 0;
-    if (tud_cdc_connected()) {
-        while (i < len) {
-            uint32_t n = len - i;
-            if (n > CFG_TUD_CDC_EP_BUFSIZE) {
-                n = CFG_TUD_CDC_EP_BUFSIZE;
-            }
+    while (i < len) {
+        uint32_t n = len - i;
+        if (n > CFG_TUD_CDC_EP_BUFSIZE) {
+            n = CFG_TUD_CDC_EP_BUFSIZE;
+        }
+        if (tud_cdc_connected()) {
             int timeout = 0;
-            // Wait with a max of USC_CDC_TIMEOUT ms
+            // If CDC port is connected but the buffer is full, wait for up to USC_CDC_TIMEOUT ms.
             while (n > tud_cdc_write_available() && timeout++ < MICROPY_HW_USB_CDC_TX_TIMEOUT) {
                 mp_event_wait_ms(1);
 
                 // Explicitly run the USB stack as the scheduler may be locked (eg we
                 // are in an interrupt handler), while there is data pending.
                 mp_usbd_task();
             }
-            if (timeout >= MICROPY_HW_USB_CDC_TX_TIMEOUT) {
+            // Limit write to available space in tx buffer when connected.
+            n = MIN(n, tud_cdc_write_available());
+            if (n == 0) {
                 break;
             }
-            uint32_t n2 = tud_cdc_write(str + i, n);
-            tud_cdc_write_flush();
-            i += n2;
         }
+        // When not connected we always write to usb fifo, ensuring it has latest data.
+        uint32_t n2 = tud_cdc_write(str + i, n);
+        tud_cdc_write_flush();
+        i += n2;
     }
     return i;
 }
 
+void tud_sof_cb(uint32_t frame_count) {
+    if (--cdc_connected_flush_delay < 0) {
+        // Finished on-connection delay, disable SOF interrupt again.
+        tud_sof_cb_enable(false);
+        tud_cdc_write_flush();
+    }
+}
+
 #endif
 
-#if MICROPY_HW_USB_CDC_1200BPS_TOUCH && MICROPY_HW_ENABLE_USBDEV
+#if MICROPY_HW_ENABLE_USBDEV && (MICROPY_HW_USB_CDC_1200BPS_TOUCH || MICROPY_HW_USB_CDC)
 
+#if MICROPY_HW_USB_CDC_1200BPS_TOUCH
 static mp_sched_node_t mp_bootloader_sched_node;
 
 static void usbd_cdc_run_bootloader_task(mp_sched_node_t *node) {
     mp_hal_delay_ms(250);
     machine_bootloader(0, NULL);
 }
+#endif
 
 void
 #if MICROPY_HW_USB_EXTERNAL_TINYUSB
@@ -137,6 +153,16 @@ mp_usbd_line_state_cb
 tud_cdc_line_state_cb
 #endif
     (uint8_t itf, bool dtr, bool rts) {
+    #if MICROPY_HW_USB_CDC && !MICROPY_EXCLUDE_SHARED_TINYUSB_USBD_CDC
+    if (dtr) {
+        // A host application has started to open the cdc serial port.
+        // Wait a few ms for host to be ready then send tx buffer.
+        // High speed connection SOF fires at 125us, full speed at 1ms.
+        cdc_connected_flush_delay = (tud_speed_get() == TUSB_SPEED_HIGH) ? 128 : 16;
+        tud_sof_cb_enable(true);
+    }
+    #endif
+    #if MICROPY_HW_USB_CDC_1200BPS_TOUCH
     if (dtr == false && rts == false) {
         // Device is disconnected.
         cdc_line_coding_t line_coding;
@@ -146,6 +172,7 @@ tud_cdc_line_state_cb
             mp_sched_schedule_node(&mp_bootloader_sched_node, usbd_cdc_run_bootloader_task);
         }
     }
+    #endif
 }
 
 #endif

shared/tinyusb/tusb_config.h

@@ -79,6 +79,7 @@
 #if CFG_TUD_CDC
 #define CFG_TUD_CDC_RX_BUFSIZE  ((CFG_TUD_MAX_SPEED == OPT_MODE_HIGH_SPEED) ? 512 : 256)
 #define CFG_TUD_CDC_TX_BUFSIZE  ((CFG_TUD_MAX_SPEED == OPT_MODE_HIGH_SPEED) ? 512 : 256)
+#define CFG_TUD_CDC_PERSISTENT_TX_BUFF (1)
 #endif
 
 // MSC Configuration