From 7fe893d48abfb0720c11666ab40db5a378a0d860 Mon Sep 17 00:00:00 2001
From: Peter Ferrie <peter.ferrie@gmail.com>
Date: Tue, 26 Nov 2019 22:17:22 -0800
Subject: [PATCH] proper FASTChip support

---
 src/constants.a |  4 ++--
 src/hw.accel.a  | 51 +++++++++++++++++++++++++++++--------------------
 2 files changed, 32 insertions(+), 23 deletions(-)

diff --git a/src/constants.a b/src/constants.a
index fd34b7bca..da02376cc 100644
--- a/src/constants.a
+++ b/src/constants.a
@@ -18,7 +18,7 @@
 ; D672..DB6D - HGR font code & ProRWTS glue code
 ; DB6E..DB7D - backup of stack (during gameplay and self-running demos)
 ; ...unused...
-; DBB6..DBFF - (de)acceleration function
+; DBB2..DBFF - (de)acceleration function
 ; DC00..DFFF - HGR font data
 ;------------------------------------------------------------------------------
 
@@ -112,7 +112,7 @@ gCheatsAvailable   = $D000  ; master cheats table, indexed by game index in gGam
 MachineStatus      = $FFF9
 
 ; LC RAM 2
-DisableAccelerator = $DBB6
+DisableAccelerator = $DBB2
 EnableAccelerator  = DisableAccelerator+3
 
 ; AND masks for MachineStatus
diff --git a/src/hw.accel.a b/src/hw.accel.a
index 2f03cb6c9..b4344ac16 100644
--- a/src/hw.accel.a
+++ b/src/hw.accel.a
@@ -118,7 +118,8 @@ fc_lock         =    $C06A
 FC_UNLOCK       =    $6A     ; write 4 times
 FC_LOCK         =    $A6
 fc_enable       =    $C06B
-fc_speed        =    $C06D
+fc_config       =    $C06E
+fc_data         =    $C06F
 FC_1MHZ         =    9
 FC_ON           =    40      ; doco says 16.6Mhz
 
@@ -193,7 +194,7 @@ maccheck
 iic
          ldx   romid_c
          cpx   #ROMID_CPLUS
-         bne   build_addon ; not a //c+, eventually hit Zip
+         bne   patch_zc ; not a //c+, eventually hit Zip
 
          lda   #<iicplus
          ldy   #>iicplus
@@ -208,6 +209,13 @@ build_setspeed
          ldx   #(end_setspeed-setspeed)
          rts
 
+patch_zc
+         lda   #$d0    ; BNE
+         sta   zc_iic
+         lda   #(FASTChip-zc_iic)-2
+         sta   zc_iic+1
+         ; fall through
+
 build_addon
          lda   #<addon
          ldy   #>addon
@@ -334,15 +342,26 @@ addon
         ; TransWarp I
          sta   tw1_speed
 
-        ; Zip Chip
+        ; trademarked accelerator from Germany
 
          tay
+         sta   uw_fast,y ; value does not matter
+
+        ; Zip Chip
+
+         ldy   #FC_1MHZ
          eor   #1
          tax
-         lda   #ZC_UNLOCK
+         beq   +
+         ldy   #FC_ON
++        lda   #ZC_UNLOCK
          php
          sei             ; timing sensitive
-         sta   zc_lock
+
+zc_iic
+         sta   zc_lock   ; SMC
+                         ; no blind Zip Chip on the IIc
+                         ; it has unwanted side-effects
          sta   zc_lock
          sta   zc_lock
          sta   zc_lock
@@ -351,29 +370,19 @@ addon
          lda   #ZC_LOCK
          sta   zc_lock
 
-        ;; current products are subject to change so do
-        ;; these last
-
-        ; trademarked accelerator from Germany
-
-         sta   uw_fast,y ; value does not matter
-
-        ; FASTChip
-
-         ldx   #FC_1MHZ
-         tya
-         bne   fcset
-         ldx   #FC_ON  ; enable set speed?
-fcset
+FASTChip
          lda   #FC_UNLOCK
          sta   fc_lock
          sta   fc_lock
          sta   fc_lock
          sta   fc_lock
          sta   fc_enable
-         stx   fc_speed
+         lda   #0
+         sta   fc_config
+         sty   fc_data
          lda   #FC_LOCK
          sta   fc_lock
+
          plp             ; restore interrupt state
          rts
-end_addon
+end_addon
\ No newline at end of file