usb: add a USB_TRACE() debugging mechanism

include/gint/usb.h

@@ -269,27 +269,28 @@ int usb_commit_sync_timeout(int pipe, timeout_t const *timeout);
 int usb_commit_async(int pipe, gint_call_t callback);
 
 //---
-// USB debugging log
+// USB debugging functions
 //---
 
 #ifdef GINT_USB_DEBUG
 #define USB_LOG(...) usb_log(__VA_ARGS__)
+#define USB_TRACE(...) usb_trace(__VA_ARGS__)
 
-/* usb_set_log(): Set the logging function for the USB driver
+/* usb_set_log(): Set the logging function for the USB driver */
-
-   The USB driver can produce logs, which are mostly useful to troubleshoot
-   problems and add new protocols. The logging is disabled by default but can
-   be enabled by specifying this function.
-
-   It is up to you whether to store that in a buffer, rotate logs, send them to
-   storage memory or a console on the PC. */
 void usb_set_log(void (*logger)(char const *format, va_list args));
-
 /* usb_log(): Send a message to the USB log */
 void usb_log(char const *format, ...);
 
+/* usb_set_trace(): Set the tracing function for the USB driver
+   The function is called atomically, thus cannot be interrupted, therefore it
+   is safe to call usb_trace() in interrupt handlers. */
+void usb_set_trace(void (*tracer)(char const *message));
+/* usb_trace(): Trace the current state of the driver */
+void usb_trace(char const *message);
+
 #else
 #define USB_LOG(...) do {} while(0)
+#define USB_TRACE(...) do {} while(0)
 #endif
 
 //---

src/usb/pipes.c

@@ -224,6 +224,8 @@ static void finish_transfer(struct transfer volatile *t, int pipe)
 	if(pipe) USB.BEMPENB.word &= ~(1 << pipe);
 
 	if(t->callback.function) gint_call(t->callback);
+
+	USB_TRACE("finish_transfer()");
 }
 
 /* finish_round(): Update transfer logic after a write round completes
@@ -252,6 +254,8 @@ static void finish_round(struct transfer volatile *t, int pipe)
 		t->data = NULL;
 		if(t->callback.function) gint_call(t->callback);
 	}
+
+	USB_TRACE("finish_round()");
 }
 
 /* write_round(): Write up to a FIFO's worth of data to a pipe
@@ -304,6 +308,8 @@ static void write_round(struct transfer volatile *t, int pipe)
 		if(t->unit_size == 4) write_32(t->data, size >> 2, FIFO);
 		if(partial) finish_round(t, pipe);
 	}
+
+	USB_TRACE("write_round()");
 }
 
 int usb_write_async(int pipe, void const *data, int size, int unit_size,

src/usb/usb.c

@@ -6,6 +6,7 @@
 #include <gint/drivers/states.h>
 #include <gint/clock.h>
 #include <gint/intc.h>
+#include <gint/cpu.h>
 #include "usb_private.h"
 
 #define USB SH7305_USB
@@ -27,10 +28,11 @@ static gint_call_t usb_open_callback = GINT_CALL_NULL;
 static bool volatile usb_open_status = false;
 
 //---
-// Logging system
+// Debugging functions
 //---
 
 static void (*usb_logger)(char const *format, va_list args) = NULL;
+static void (*usb_tracer)(char const *message) = NULL;
 
 void usb_set_log(void (*logger)(char const *format, va_list args))
 {
@@ -40,13 +42,26 @@ void usb_set_log(void (*logger)(char const *format, va_list args))
 void usb_log(char const *format, ...)
 {
 	if(!usb_logger) return;
-
 	va_list args;
 	va_start(args, format);
 	usb_logger(format, args);
 	va_end(args);
 }
 
+void usb_set_trace(void (*tracer)(char const *message))
+{
+	usb_tracer = tracer;
+}
+
+void usb_trace(char const *message)
+{
+	if(usb_tracer) {
+		cpu_atomic_start();
+		usb_tracer(message);
+		cpu_atomic_end();
+	}
+}
+
 //---
 // Module powering and depowering
 //---