Perform small writes before sending OK.

To speed up downloads, OpenOCD sends gdb OK when a write is received,
even before the write has actually occurred. The failure is then
returned for the next write. That leads to the following confusing
behavior:
```
(gdb) p/x *((int*)0xdeadbeef)=8675309
$2 = 0x845fed
(gdb) p/x *((int*)0x80000000)=6874742
Cannot access memory at address 0x80000000
```
While it's actually the first write that failed.

This change hacks around this problem by not sending OK for small writes
(len<8) until the write has actually occurred. This does not impact
download speed, since during downloads (almost) all writes will have
much larger length.

Change-Id: I1f8b9bb19b0707487f840df6871e372e4ba228dd
Signed-off-by: Tim Newsome <tim@sifive.com>
Reviewed-on: http://openocd.zylin.com/3803
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>

diff --git a/src/server/gdb_server.c b/src/server/gdb_server.c
index f85fa1bde9d8ffbe82b0190a13cfb2ba5e841328..7fd579b4651170052c78dd53e0a6119e11167ab3 100644 (file)
--- a/src/server/gdb_server.c
+++ b/src/server/gdb_server.c
@@ -1473,6 +1473,10 @@ static int gdb_write_memory_binary_packet(struct connection *connection,
        uint32_t len = 0;
 
        int retval = ERROR_OK;
+       /* Packets larger than fast_limit bytes will be acknowledged instantly on
+        * the assumption that we're in a download and it's important to go as fast
+        * as possible. */
+       uint32_t fast_limit = 8;
 
        /* skip command character */
        packet++;
@@ -1493,19 +1497,23 @@ static int gdb_write_memory_binary_packet(struct connection *connection,
 
        struct gdb_connection *gdb_connection = connection->priv;
 
-       if (gdb_connection->mem_write_error) {
+       if (gdb_connection->mem_write_error)
                retval = ERROR_FAIL;
-               /* now that we have reported the memory write error, we can clear the condition */
-               gdb_connection->mem_write_error = false;
-       }
 
-       /* By replying the packet *immediately* GDB will send us a new packet
-        * while we write the last one to the target.
-        */
-       if (retval == ERROR_OK)
-               gdb_put_packet(connection, "OK", 2);
-       else {
+       if (retval == ERROR_OK) {
+               if (len >= fast_limit) {
+                       /* By replying the packet *immediately* GDB will send us a new packet
+                        * while we write the last one to the target.
+                        * We only do this for larger writes, so that users who do something like:
+                        * p *((int*)0xdeadbeef)=8675309
+                        * will get immediate feedback that that write failed.
+                        */
+                       gdb_put_packet(connection, "OK", 2);
+               }
+       } else {
                retval = gdb_error(connection, retval);
+               /* now that we have reported the memory write error, we can clear the condition */
+               gdb_connection->mem_write_error = false;
                if (retval != ERROR_OK)
                        return retval;
        }
@@ -1518,6 +1526,15 @@ static int gdb_write_memory_binary_packet(struct connection *connection,
                        gdb_connection->mem_write_error = true;
        }
 
+       if (len < fast_limit) {
+               if (retval != ERROR_OK) {
+                       gdb_error(connection, retval);
+                       gdb_connection->mem_write_error = false;
+               } else {
+                       gdb_put_packet(connection, "OK", 2);
+               }
+       }
+
        return ERROR_OK;
 }