mimxrt: Fix USB CDC handling so it works reliably.

On i.MX the SysTick IRQ cannot wake the CPU from a WFI so the CPU was blocked on WFI waiting for USB data in mp_hal_stdin_rx_chr() even though it had already arrived (because it may arrive just after calling the check tud_cdc_available()). This commit fixes this problem by using SEV/WFE to indicate that there has been a USB event. The mp_hal_stdout_tx_strn() function is also fixed so that it doesn't overflow the USB buffers. Signed-off-by: Damien George <damien@micropython.org>
micropython · Feb 12, 2021 · f31c6b4 · f31c6b4
1 parent c9260dd
commit f31c6b4
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Showing 3 changed files with 11 additions and 10 deletions.
diff --git a/ports/mimxrt/board_init.c b/ports/mimxrt/board_init.c
@@ -92,9 +92,11 @@ void SysTick_Handler(void) {
 void USB_OTG1_IRQHandler(void) {
     tud_int_handler(0);
     tud_task();
+    __SEV();
 }
 
 void USB_OTG2_IRQHandler(void) {
     tud_int_handler(1);
     tud_task();
+    __SEV();
 }
diff --git a/ports/mimxrt/mpconfigport.h b/ports/mimxrt/mpconfigport.h
@@ -94,7 +94,7 @@ extern const struct _mp_obj_module_t mp_module_utime;
     do { \
         extern void mp_handle_pending(bool); \
         mp_handle_pending(true); \
-        __WFI(); \
+        __WFE(); \
     } while (0);
 
 #define MICROPY_MAKE_POINTER_CALLABLE(p) ((void *)((mp_uint_t)(p) | 1))

diff --git a/ports/mimxrt/mphalport.c b/ports/mimxrt/mphalport.c
@@ -75,25 +75,24 @@ int mp_hal_stdin_rx_chr(void) {
                 return buf[0];
             }
         }
-        __WFI();
+        MICROPY_EVENT_POLL_HOOK
     }
 }
 
 void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
     if (tud_cdc_connected()) {
         for (size_t i = 0; i < len;) {
             uint32_t n = len - i;
-            uint32_t n2 = tud_cdc_write(str + i, n);
-            if (n2 < n) {
-                while (!tud_cdc_write_flush()) {
-                    __WFI();
-                }
+            if (n > CFG_TUD_CDC_EP_BUFSIZE) {
+                n = CFG_TUD_CDC_EP_BUFSIZE;
             }
+            while (n > tud_cdc_write_available()) {
+                __WFE();
+            }
+            uint32_t n2 = tud_cdc_write(str + i, n);
+            tud_cdc_write_flush();
             i += n2;
         }
-        while (!tud_cdc_write_flush()) {
-            __WFI();
-        }
     }
     // TODO
     // while (len--) {