Gary Carlson <gcarlson@carlson-minot.com>:

Fix intermittent J-Link interface startup failures:
- Use usb_reset to ensure selected dongle is in known good state.
- Assert emulator reset durning status check to prevent supurious failures.
- Eliminate status check loop; not needed due to other fixes.

git-svn-id: svn://svn.berlios.de/openocd/trunk@2471 b42882b7-edfa-0310-969c-e2dbd0fdcd60

diff --git a/src/jtag/jlink.c b/src/jtag/jlink.c
index 56187e2e2be8ed57e9cb2748d13a9c69b57a2e75..b41731d2dc4e2255dfc976185479c76535f6d0ef 100644 (file)
--- a/src/jtag/jlink.c
+++ b/src/jtag/jlink.c
@@ -305,7 +305,6 @@ static int jlink_register_commands(struct command_context_s *cmd_ctx)
 
 static int jlink_init(void)
 {
-       int check_cnt;
        int i;
 
        jlink_jtag_handle = jlink_usb_open();
@@ -315,24 +314,28 @@ static int jlink_init(void)
                LOG_ERROR("Cannot find jlink Interface! Please check connection and permissions.");
                return ERROR_JTAG_INIT_FAILED;
        }
+       
+       /*
+        *  The next three instructions were added after discovering a problem while using an oscilloscope.  For the V8
+        *      SAM-ICE dongle (and likely other j-link device variants), the reset line to the target microprocessor was found to
+        *      cycle only intermittently during emulator startup (even after encountering the downstream reset instruction later
+        *      in the code).  This was found to create two issues:  1) In general it is a bad practice to not reset a CPU to a known
+        *      state when starting an emulator and 2) something critical happens inside the dongle when it does the first read
+        *      following a new USB session.  Keeping the processor in reset during the first read collecting version information
+        *      seems to prevent errant "J-Link command EMU_CMD_VERSION failed" issues.
+        */
+       
+       LOG_INFO("J-Link initialization started / target CPU reset initiated");
+       jlink_simple_command(EMU_CMD_HW_TRST0);
+       jlink_simple_command(EMU_CMD_HW_RESET0);
+       sleep(1);
 
        jlink_hw_jtag_version = 2;
-       check_cnt = 0;
-       while (check_cnt < 3)
-       {
-               if (jlink_get_version_info() == ERROR_OK)
-               {
-                       /* attempt to get status */
-                       jlink_get_status();
-                       break;
-               }
-
-               check_cnt++;
-       }
 
-       if (check_cnt == 3)
+       if (jlink_get_version_info() == ERROR_OK)
        {
-               LOG_INFO("J-Link initial read failed, don't worry");
+               /* attempt to get status */
+               jlink_get_status();
        }
 
        LOG_INFO("J-Link JTAG Interface ready");
@@ -860,6 +863,15 @@ static jlink_jtag_t* jlink_usb_open()
                        if ((dev->descriptor.idVendor == VID) && (dev->descriptor.idProduct == PID))
                        {
                                result->usb_handle = usb_open(dev);
+                               
+                               /*
+                                *      Some j-link dongles experience intermittent communication issues at startup to varying degrees
+                                *      depending on the host operating system.  Troubleshooting this problem all the way back to libusb
+                                *      revealed that without a usb reset, the hardware can start in an uncertain state causing a litany
+                                *      of annoying problems.  The next step was added to the original code to address this problem.
+                                */
+                               
+                               usb_reset(result->usb_handle);
 
                                /* usb_set_configuration required under win32 */
                                usb_set_configuration(result->usb_handle, dev->config[0].bConfigurationValue);