Fix: re-introduce testing for magic byte

1 files changed, 37 insertions, 6 deletions

diff --git a/firmware/usbdrv/usbdrvasm165.inc b/firmware/usbdrv/usbdrvasm165.inc
index ae91588..450d2fd 100644
--- a/firmware/usbdrv/usbdrvasm165.inc
+++ b/firmware/usbdrv/usbdrvasm165.inc
@@ -4,7 +4,9 @@
  * Creation Date: 2007-04-22
  * Tabsize: 4
  * Copyright: (c) 2007 by OBJECTIVE DEVELOPMENT Software GmbH
+ * Portions Copyright: (c) 2012 Louis Beaudoin
  * License: GNU GPL v2 (see License.txt), GNU GPL v3 or proprietary (CommercialLicense.txt)
+ * Revision: $Id: usbdrvasm165.inc 740 2009-04-13 18:23:31Z cs $
  */
 
 /* Do not link this file! Link usbdrvasm.S instead, which includes the
@@ -34,12 +36,41 @@ of CPU cycles, but even an exact number of cycles!
 ; Numbers in brackets are clocks counted from center of last sync bit
 ; when instruction starts
 
+; the code enabled by TINY85MODE is inteded only for use with the tiny85-compatible USBaspLoader
+; project.  
+; with TINY85MODE set, the beginning of the ISR checks for a magic word "B007" at the very bottom of the stack
+; and jumps to the application's ISR if the magic word isn't present
+; the max allowable interrupt latency is lower given this additional code before getting to the 
+; USB-specific portion of the ISR.
 
 USB_INTR_VECTOR:
 ;order of registers pushed: YL, SREG [sofError], r0, YH, shift, x1, x2, x3, x4, cnt
-    push    YL                  ;[-23] push only what is necessary to sync with edge ASAP
-    in      YL, SREG            ;[-21]
-    push    YL                  ;[-20]
+    push    YL              ; push only what is necessary to sync with edge ASAP
+    in      YL, SREG				; 
+    push    YL						; 
+
+#ifdef TINY85MODE
+; look for magic word "B007" at the bottom of the stack
+	lds YL, RAMEND
+	cpi YL, 0xB0
+	brne cleanupAndJumpToApp
+
+	lds YL, RAMEND-1
+	cpi YL, 0x07
+	breq cleanupBootloaderIntStack
+
+cleanupAndJumpToApp:
+; magic word was not found, put registers back to where they were before this ISR ran, and jump to application ISR
+	pop YL
+	out      SREG, YL
+	pop YL
+	
+	rjmp __vectors - TINYVECTOR_USBPLUS_OFFSET
+
+cleanupBootloaderIntStack:
+; magic word was found, put registers 
+	CLR YL					; [-19] ensure we meet below requirements for YL < 0x80 
+#endif
 ;----------------------------------------------------------------------------
 ; Synchronize with sync pattern:
 ;----------------------------------------------------------------------------
@@ -49,9 +80,9 @@ USB_INTR_VECTOR:
 ;YL is guarenteed to be < 0x80 because I flag is clear. When we jump to
 ;waitForJ, ensure that this prerequisite is met.
 waitForJ:
-    inc     YL
-    sbis    USBIN, USBMINUS
-    brne    waitForJ        ; just make sure we have ANY timeout
+    inc     YL				; [-18]
+    sbis    USBIN, USBMINUS ; [-17]
+    brne    waitForJ        ; [-16] just make sure we have ANY timeout
 waitForK:
 ;The following code results in a sampling window of < 1/4 bit which meets the spec.
     sbis    USBIN, USBMINUS     ;[-15]