mimxrt/mphalport: Fix USB CDC RX handling to not block when unprocessed.

Changes in this commit:
- Fix USB CDC RX handling to not block when unprocessed.  The fix follows
  587339022689187a1acbccc1d0e2425a67385ff7.
- Fix dupterm rx.
- Remove some obsolete lines.

2 files changed, 49 insertions, 37 deletions

diff --git a/ports/mimxrt/Makefile b/ports/mimxrt/Makefile
index f9c5bf402..985ece084 100644
--- a/ports/mimxrt/Makefile
+++ b/ports/mimxrt/Makefile
@@ -256,6 +256,7 @@ SRC_C += \
 	shared/netutils/dhcpserver.c \
 	shared/readline/readline.c \
 	shared/runtime/gchelper_native.c \
+	shared/runtime/interrupt_char.c \
 	shared/runtime/mpirq.c \
 	shared/runtime/pyexec.c \
 	shared/runtime/stdout_helpers.c \
diff --git a/ports/mimxrt/mphalport.c b/ports/mimxrt/mphalport.c
index 673b58b23..46349d3a3 100644
--- a/ports/mimxrt/mphalport.c
+++ b/ports/mimxrt/mphalport.c
@@ -29,68 +29,82 @@
 #include "py/stream.h"
 #include "py/mphal.h"
 #include "shared/timeutils/timeutils.h"
+#include "shared/runtime/interrupt_char.h"
 #include "extmod/misc.h"
 #include "ticks.h"
 #include "tusb.h"
 #include "fsl_snvs_lp.h"
 
-#if FSL_COMMON_DRIVER_VERSION != 0x020001
-#include "fsl_ocotp.h"
-#else
-void OCOTP_Init(OCOTP_Type *base, uint32_t srcClock_Hz);
+#ifndef MICROPY_HW_STDIN_BUFFER_LEN
+#define MICROPY_HW_STDIN_BUFFER_LEN 512
 #endif
 
 #include CPU_HEADER_H
 
-STATIC uint8_t stdin_ringbuf_array[260];
+STATIC uint8_t stdin_ringbuf_array[MICROPY_HW_STDIN_BUFFER_LEN];
 ringbuf_t stdin_ringbuf = {stdin_ringbuf_array, sizeof(stdin_ringbuf_array), 0, 0};
 
-#if MICROPY_KBD_EXCEPTION
-
-int mp_interrupt_char = -1;
-
-void tud_cdc_rx_wanted_cb(uint8_t itf, char wanted_char) {
-    (void)itf;
-    (void)wanted_char;
-    tud_cdc_read_char(); // discard interrupt char
-    mp_sched_keyboard_interrupt();
+uint8_t cdc_itf_pending; // keep track of cdc interfaces which need attention to poll
+
+void poll_cdc_interfaces(void) {
+    // any CDC interfaces left to poll?
+    if (cdc_itf_pending && ringbuf_free(&stdin_ringbuf)) {
+        for (uint8_t itf = 0; itf < 8; ++itf) {
+            if (cdc_itf_pending & (1 << itf)) {
+                tud_cdc_rx_cb(itf);
+                if (!cdc_itf_pending) {
+                    break;
+                }
+            }
+        }
+    }
 }
 
-void mp_hal_set_interrupt_char(int c) {
-    mp_interrupt_char = c;
-    tud_cdc_set_wanted_char(c);
-}
 
-#endif
+void tud_cdc_rx_cb(uint8_t itf) {
+    // consume pending USB data immediately to free usb buffer and keep the endpoint from stalling.
+    // in case the ringbuffer is full, mark the CDC interface that need attention later on for polling
+    cdc_itf_pending &= ~(1 << itf);
+    for (uint32_t bytes_avail = tud_cdc_n_available(itf); bytes_avail > 0; --bytes_avail) {
+        if (ringbuf_free(&stdin_ringbuf)) {
+            int data_char = tud_cdc_read_char();
+            if (data_char == mp_interrupt_char) {
+                mp_sched_keyboard_interrupt();
+            } else {
+                ringbuf_put(&stdin_ringbuf, data_char);
+            }
+        } else {
+            cdc_itf_pending |= (1 << itf);
+            return;
+        }
+    }
+}
 
 uintptr_t mp_hal_stdio_poll(uintptr_t poll_flags) {
     uintptr_t ret = 0;
+    poll_cdc_interfaces();
     if ((poll_flags & MP_STREAM_POLL_RD) && ringbuf_peek(&stdin_ringbuf) != -1) {
         ret |= MP_STREAM_POLL_RD;
     }
-    if (tud_cdc_connected() && tud_cdc_available()) {
-        ret |= MP_STREAM_POLL_RD;
-    }
+    #if MICROPY_PY_OS_DUPTERM
+    ret |= mp_uos_dupterm_poll(poll_flags);
+    #endif
     return ret;
 }
 
 int mp_hal_stdin_rx_chr(void) {
     for (;;) {
-        // TODO
-        // if (USARTx->USART.INTFLAG.bit.RXC) {
-        //     return USARTx->USART.DATA.bit.DATA;
-        // }
+        poll_cdc_interfaces();
         int c = ringbuf_get(&stdin_ringbuf);
         if (c != -1) {
             return c;
         }
-        if (tud_cdc_connected() && tud_cdc_available()) {
-            uint8_t buf[1];
-            uint32_t count = tud_cdc_read(buf, sizeof(buf));
-            if (count) {
-                return buf[0];
-            }
+        #if MICROPY_PY_OS_DUPTERM
+        int dupterm_c = mp_uos_dupterm_rx_chr();
+        if (dupterm_c >= 0) {
+            return dupterm_c;
         }
+        #endif
         MICROPY_EVENT_POLL_HOOK
     }
 }
@@ -110,12 +124,9 @@ void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
             i += n2;
         }
     }
+    #if MICROPY_PY_OS_DUPTERM
     mp_uos_dupterm_tx_strn(str, len);
-    // TODO
-    // while (len--) {
-    //     while (!(USARTx->USART.INTFLAG.bit.DRE)) { }
-    //     USARTx->USART.DATA.bit.DATA = *str++;
-    // }
+    #endif
 }
 
 uint64_t mp_hal_time_ns(void) {