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Workaround Z280 CPU Bug for LZSA2

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The LZSA2 decompressor invoked a known Z280 CPU bug.  A small modification to the code resolves this.
This commit is contained in:
Wayne Warthen
2023-05-07 17:45:43 -07:00
parent 9358299f14
commit c628ba10f2
4 changed files with 15 additions and 11 deletions
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2
Source/HBIOS/cfg_rcz280.asm
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@@ -20,7 +20,7 @@ CPUFAM .EQU CPU_Z280 ; CPU FAMILY: CPU_[Z80|Z180|Z280]
BIOS .EQU BIOS_WBW ; HARDWARE BIOS: BIOS_[WBW|UNA]
BATCOND .EQU FALSE ; ENABLE LOW BATTERY WARNING MESSAGE
HBIOS_MUTEX .EQU FALSE ; ENABLE REENTRANT CALLS TO HBIOS (ADDS OVERHEAD)
USELZSA2 .EQU FALSE ; ENABLE FONT COMPRESSION
USELZSA2 .EQU TRUE ; ENABLE FONT COMPRESSION
TICKFREQ .EQU 50 ; DESIRED PERIODIC TIMER INTERRUPT FREQUENCY (HZ)
;
BOOT_TIMEOUT .EQU -1 ; AUTO BOOT TIMEOUT IN SECONDS, -1 TO DISABLE, 0 FOR IMMEDIATE

20
Source/HBIOS/unlzsa2s.asm
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@@ -60,8 +60,8 @@
; 3. This notice may not be removed or altered from any source distribution.
;
; #DEFINE BACKWARD_DECOMPRESS ; uncomment for data compressed with option -b (+5 bytes, -3% speed)
; #DEFINE AVOID_SELFMODIFYING_CODE ; uncomment to disallow self-modifying code (-1 byte, -4% speed)
; #DEFINE BACKWARD_DECOMPRESS ; uncomment for data compressed with option -b (+5 bytes, -3% speed)
; #DEFINE AVOID_SELFMODIFYING_CODE ; uncomment to disallow self-modifying code (-1 byte, -4% speed)
#IFNDEF BACKWARD_DECOMPRESS
@@ -79,7 +79,7 @@
#DEFINE ADD_OFFSET \
#DEFCONT \ ld a,e \ sub l \ ld l,a
#DEFCONT \ ld a,d \ sbc h \ ld h,a ; 6*4 = 24t / 6 bytes
#DEFCONT \ ld a,d \ sbc h \ ld h,a ; 6*4 = 24t / 6 bytes
#DEFINE BLOCKCOPY \
#DEFCONT \ lddr
@@ -118,7 +118,7 @@ MatchLen: and %00000111 \ add a,2 \ cp 9
call z,ExtendedCode
CopyMatch: ld c,a
push hl ; BC = len, DE = dest, HL = -offset, SP -> [src]
push hl ; BC = len, DE = dest, HL = -offset, SP -> [src]
#IFNDEF AVOID_SELFMODIFYING_CODE
PrevOffset .EQU $+1 \ ld hl,0
@@ -126,8 +126,8 @@ PrevOffset .EQU $+1 \ ld hl,0
push ix \ pop hl
#ENDIF
ADD_OFFSET
BLOCKCOPY ; BC = 0, DE = dest
pop hl ; HL = src
BLOCKCOPY ; BC = 0, DE = dest
pop hl ; HL = src
ReadToken: ld a,(hl) \ NEXT_HL \ push af
and %00011000 \ jr z,NoLiterals
@@ -163,12 +163,16 @@ ExtendedCode: call ReadNibble \ inc a \ jr z,ExtraByte
ExtraByte ld a,15 \ add a,c \ add a,(hl) \ NEXT_HL \ ret nc
ld a,(hl) \ NEXT_HL
ld b,(hl) \ NEXT_HL \ ret nz
pop bc ; RET is not needed, because RET from ReadNibble is sufficient
pop bc ; RET is not needed, because RET from ReadNibble is sufficient
ReadNibble: ld c,a
skipLDCA xor a \ ex af,af' \ ret m
skipLDCA xor a \ nop \ ex af,af' \ ret m ; NOP for Z280 bug
ld a,(hl) \ or $F0 \ ex af,af'
ld a,(hl) \ NEXT_HL \ or $0F
rrca \ rrca \ rrca \ rrca \ ret
; The extraneous NOP instruction above is to workaround a bug in the
; Z280 processor where ex af,af' can copy rather than swap the flags
; register.
; See https://www.retrobrewcomputers.org/forum/index.php?t=msg&goto=10183&