[firmware] add missing knock-knock code

This program gets loaded into the PIC on the ADK
baseboard. It controls the erase line on the SAM3X.
When it receives the proper signal from the host,
it will erase the flash memory on the SAM3X.

Change-Id: I2f2838ccc75871fc2777a87bd9be34a19848fcc6

2 files changed, 111 insertions, 0 deletions

diff --git a/hardware/eraser.asm b/hardware/eraser.asm
new file mode 100644
index 0000000..f0a2311
--- /dev/null
+++ b/hardware/eraser.asm
@@ -0,0 +1,101 @@
+; 
+;  Copyright (C) 2012 The Android Open Source Project
+; 
+;  Licensed under the Apache License, Version 2.0 (the "License");
+;  you may not use this file except in compliance with the License.
+;  You may obtain a copy of the License at
+; 
+;       http://www.apache.org/licenses/LICENSE-2.0
+;
+;  Unless required by applicable law or agreed to in writing, software
+;  distributed under the License is distributed on an "AS IS" BASIS,
+;  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+;  See the License for the specific language governing permissions and
+;  limitations under the License.
+
+; ADK2 Sam3X Eraser Controller
+; Author: Fuller
+
+; serial DTR line as clock on GP0
+; serial RTS line as data on GP1
+; GP2 output controls Sam3X erase feature
+; GP0, input, /DTR
+; GP1, input, /RTS
+; GP2, output, erase
+; GP3, input, internal pull-up, floating
+
+    #include "P10F200.INC"
+; configuration bits
+    __CONFIG (_WDT_OFF&_CP_ON&_MCLRE_OFF)
+
+; memory map
+; only 16 bytes of RAM starting at 0x10
+    udata
+GPIO_sampled    res 1
+GPIO_sampledQ   res 1
+magicKeyL       res 1
+magicKeyH       res 1
+tick0           res 1
+tick1           res 1
+
+    code        0x00
+; initialize microcontroller
+        movlw   (1<<NOT_GPWU|1<<PS2|1<<PS1|1<<PS0)  ; no wake up, pull-ups
+                                             ; TMR0 at 1:256 for low power
+        option
+        bcf     GPIO, GP2
+        movlw   (1<<GP3|1<<GP1|1<<GP0)    ; GP2 is only output
+        tris    GPIO
+
+; initialize variables
+        clrf    magicKeyH
+        clrf    magicKeyL
+        bsf     GPIO_sampled, GP0         ; can't get false rise if assume high
+
+sampler:
+        movf    GPIO_sampled, W           ; old stale sample
+        movwf   GPIO_sampledQ             ; clock pipe for edge detection
+        movf    GPIO, W                   ; fresh sample
+        movwf   GPIO_sampled              ; sampled copy of IO's
+; check for rising clock edge
+        btfss   GPIO_sampled, GP0
+        goto    sampler                   ; if not set, then it's not rising
+        btfsc   GPIO_sampledQ, GP0        ; if old is clear, then rising
+        goto    sampler
+
+shifter:
+        movf    GPIO, W                   ; sample the data
+        movwf   GPIO_sampledQ             ; reuse the same memory location
+        btfss   GPIO_sampledQ, GP0
+        goto    sampler                   ; if clock has already dropped, abort
+        bsf     STATUS, C
+        btfss   GPIO_sampledQ, GP1        ; sets C to match GP1 for shift in
+        bcf     STATUS, C
+        rrf     magicKeyH                 ; first half of..
+        rrf     magicKeyL                 ; 16-bit shift through C
+        movlw   0xac
+        subwf   magicKeyH, W
+        btfss   STATUS, Z                 ; check for key-pattern match
+        goto    sampler
+        movlw   0x5a
+        subwf   magicKeyL, W
+        btfss   STATUS, Z                 ; check for key-pattern match
+        goto    sampler
+erase:
+; begin erase trigger
+        bsf     GPIO, GP2
+; delay for erase trigger period, estimate 393mS for this code...
+delay:
+        clrf    tick0
+        clrf    tick1
+delayLoop:
+; inc16
+        incf    tick0
+        btfsc   STATUS, Z
+        incf    tick1
+        btfss   STATUS, Z
+        goto    delayLoop
+; end erase trigger
+        bcf     GPIO, GP2
+        goto    sampler
+    end
diff --git a/hardware/eraser.hex b/hardware/eraser.hex
new file mode 100644
index 0000000..586f178
--- /dev/null
+++ b/hardware/eraser.hex
@@ -0,0 +1,10 @@
+:020000040000FA
+:10000000870C020046040B0C0600730072001005FA
+:1000100010023100060230001007080A1106080A13
+:10002000060231001107080A0305310703043303F0
+:100030003203AC0C93004307080A5A0C92004307A2
+:10004000080A460574007500B4024306B50243076A
+:06005000240A4604080A20
+:040056000008000896
+:021FFE00E30FEF
+:00000001FF