ucos2.patch

This patch fixes a bug present when passing the OS_TASK_OPT_STK_CLR
option to OSTaskCreateExt().  The original code would overwrite an
additional byte past the end of the stack, wrapping to address 0 of
the current 64KB page if the stack ended on a 64KB boundary (e.g.,
erasing 0x60000 if the stack ends at 0x6FFFF).

The uC/OS-II source isn't included in the Open Source GitHub code
repository, so you will need to manually apply this using `patch`:

    patch -p1 --forward < ucos2.patch

Include the command-line option "--dry-run" to test the patch.  The
"--forward" option ignores the patch if already applied.

--- a/Lib/UCOS2/OS_TASK.C	2017-06-28 17:43:41 -0700
+++ b/Lib/UCOS2/OS_TASK.C	2019-06-14 12:37:46 -0700
@@ -439,8 +439,6 @@
     auto INT8U    err;
     auto INT16U   i;
     auto INT16U   pbos;
-    auto INT8U    upper_nibble;
-    auto INT16U   lower_16;
     auto INT16U   stk_size;
     auto INT32U   PhysAddr;
 
@@ -460,25 +458,9 @@
         if (opt & OS_TASK_OPT_STK_CHK) {          // See if stack checking has been enabled
             if (opt & OS_TASK_OPT_STK_CLR) {      // See if stack needs to be cleared
                                                   // Yes, fill the stack with zeros
-                lower_16 = (INT16U)PhysAddr;
-                upper_nibble = (INT8U)(PhysAddr >> 16);
-                for (i = stk_size; i > 0; i--) {
-                    #asm
-  							 ld	hl,@sp+upper_nibble
-							 add	hl,sp
-	                   ld   a,(hl)	         ;a gets high nibble
-							 ld	hl,@sp+lower_16
-							 add	hl,sp
-                      ld   hl,(hl)	         ;hl has lower 16 bits
-                      push ix
-                      ld   ix,hl             ;a:ix 20-bit phys addr for stack
-                      bool hl
-                      ld   l,h               ;zero hl
-                      ldp  (ix),hl           ;write zero into stack
-                      pop  ix
-                    #endasm
-                    lower_16--;
-                }
+                // PhysAddr is the last address of the stack (e.g., ...FF), so it's
+                // necessary to add 1 to get to the starting address of the stack.
+                xmemset(PhysAddr - stk_size + 1, 0, stk_size);
             }
         }