NOTICE: list the serial-bus fixes that leave the bus released

Serial bus: UNLSN, UNTLK, and a missing device leave the bus released
UNLSN ended through iec_set_idle, which pulls CLK, so the C64 kept holding CLK after UNLISTEN. UNTLK waited for the talker to pull CLK, which no device does after UNTALK, timed out, and left CLK pulled with carry set. And a serial routine that found no device also left CLK pulled. A fastloader that waits for the drive to pull CLK after the KERNAL's UNLSN (Turrican's) then went on too early. The contract (Michael Steil, "Commodore Peripheral Bus: Part 4", https://www.pagetable.com/?p=1135): at the end of a transmission the sender releases CLK and the receivers release DATA, so the bus is idle again, and the controller releases ATN after each command; after UNTALK "the current talker will then release the bus" (Part 2, https://www.pagetable.com/?p=1031). UNLSN and UNTLK now share their end and release CLK and DATA; the device-not-present exit releases ATN, CLK, and DATA. Commodore's ROMs leave the same lines in the same scenarios, as differential tests in arnitech show. Not reported upstream (https://github.com/MEGA65/open-roms).
2026-10-15 14:21:36 +02:00 · 2026-10-15 14:21:36 +02:00 · 2026-10-15 02:50:48 +02:00 · 2026-10-15 02:50:48 +02:00 · 2026-10-15 02:32:03 +02:00 · 2026-10-15 02:31:56 +02:00
12 changed files with 229 additions and 15 deletions
@@ -137,6 +137,7 @@ GEN_ZMAC_H     = $(DIR_ZMAC_TMP)/doc.inl
 # List of build directories

 DIR_C64        = build/target_c64
+DIR_MC64       = build/target_mc64
 DIR_CUS        = build/target_custom
 DIR_GEN        = build/target_generic
 DIR_GENCRT     = build/target_generic_crt
@@ -151,6 +152,7 @@ DIR_X16        = build/target_cx16

 CFG_CUS        = src/,,config_custom.s 
 CFG_C64        = src/,,config_c64.s
+CFG_MC64       = src/,,config_mc64.s
 CFG_GEN        = src/,,config_generic.s
 CFG_GENCRT     = src/,,config_generic_crt.s
 CFG_TST38      = src/,,config_testing_38K.s
@@ -164,6 +166,7 @@ CFG_U64CRT     = src/,,config_ultimate64_crt.s

 GEN_STR_CUS    = $(DIR_CUS)/,generated/,packed_strings.s
 GEN_STR_C64    = $(DIR_C64)/,generated/,packed_strings.s
+GEN_STR_MC64   = $(DIR_MC64)/,generated/,packed_strings.s
 GEN_STR_GEN    = $(DIR_GEN)/,generated/,packed_strings.s
 GEN_STR_GENCRT = $(DIR_GENCRT)/,generated/,packed_strings.s
 GEN_STR_TST38  = $(DIR_TST38)/,generated/,packed_strings.s
@@ -212,6 +215,7 @@ TARGET_CHR_PXL     = build/chargen_pxlfont.rom

 TARGET_CUS_B       = build/basic_custom.rom
 TARGET_C64_B       = build/basic_c64.rom
+TARGET_MC64_B      = build/basic_mc64.rom
 TARGET_GEN_B       = build/basic_generic.rom
 TARGET_GENCRT_B    = build/basic_generic_crt.rom
 TARGET_TST38_B     = build/basic_testing_38K.rom
@@ -221,6 +225,7 @@ TARGET_U64CRT_B    = build/basic_ultimate64_crt.rom

 TARGET_CUS_K       = build/kernal_custom.rom
 TARGET_C64_K       = build/kernal_c64.rom
+TARGET_MC64_K      = build/kernal_mc64.rom
 TARGET_GEN_K       = build/kernal_generic.rom
 TARGET_GENCRT_K    = build/kernal_generic_crt.rom
 TARGET_TST38_K     = build/kernal_testing_38K.rom
@@ -237,6 +242,7 @@ TARGET_X16_x       = build/cx16-dummy.rom

 TARGET_LIST_CUS    = $(TARGET_CUS_B) $(TARGET_CUS_K)
 TARGET_LIST_C64    = $(TARGET_C64_B) $(TARGET_C64_K)
+TARGET_LIST_MC64   = $(TARGET_MC64_B) $(TARGET_MC64_K)
 TARGET_LIST_GEN    = $(TARGET_GEN_B) $(TARGET_GEN_K)
 TARGET_LIST_GENCRT = $(TARGET_GENCRT_B) $(TARGET_GENCRT_K) $(TARGET_GENCRT_X)
 TARGET_LIST_TST38  = $(TARGET_TST38_B) $(TARGET_TST38_K)
@@ -249,6 +255,7 @@ TARGET_Z80TEST     = ./build/cpm/Z80TEST.COM
 TARGET_LIST        = $(TARGET_CHR_ORF)     \
                     $(TARGET_LIST_CUS)    \
                     $(TARGET_LIST_C64)    \
+                     $(TARGET_LIST_MC64)   \
                     $(TARGET_LIST_GEN)    \
                     $(TARGET_LIST_GENCRT) \
                     $(TARGET_LIST_TST38)  \
@@ -385,6 +392,8 @@ $(DIR_CUS)/OUTB_x.BIN $(DIR_CUS)/BASIC_combined.vs: \
    $(TOOL_ASSEMBLER) $(TOOL_BUILD_SEGMENT) $(DEP_BASIC) $(CFG_CUS) $(GEN_STR_CUS) $(DIR_CUS)/KERNAL_combined.sym
 $(DIR_C64)/OUTB_x.BIN $(DIR_C64)/BASIC_combined.vs: \
    $(TOOL_ASSEMBLER) $(TOOL_BUILD_SEGMENT) $(DEP_BASIC) $(CFG_C64) $(GEN_STR_C64) $(DIR_C64)/KERNAL_combined.sym
+$(DIR_MC64)/OUTB_x.BIN $(DIR_MC64)/BASIC_combined.vs: \
+    $(TOOL_ASSEMBLER) $(TOOL_BUILD_SEGMENT) $(DEP_BASIC) $(CFG_MC64) $(GEN_STR_MC64) $(DIR_MC64)/KERNAL_combined.sym
 $(DIR_GEN)/OUTB_x.BIN $(DIR_GEN)/BASIC_combined.vs: \
    $(TOOL_ASSEMBLER) $(TOOL_BUILD_SEGMENT) $(DEP_BASIC) $(CFG_GEN) $(GEN_STR_GEN) $(DIR_GEN)/KERNAL_combined.sym
 $(DIR_TST38)/OUTB_x.BIN $(DIR_TST38)/BASIC_combined.vs: \
@@ -398,6 +407,8 @@ $(DIR_CUS)/OUTK_x.BIN $(DIR_CUS)/KERNAL_combined.vs $(DIR_CUS)/KERNAL_combined.s
    $(TOOL_ASSEMBLER) $(TOOL_BUILD_SEGMENT) $(DEP_KERNAL) $(CFG_CUS) $(GEN_STR_CUS)
 $(DIR_C64)/OUTK_x.BIN $(DIR_C64)/KERNAL_combined.vs $(DIR_C64)/KERNAL_combined.sym: \
    $(TOOL_ASSEMBLER) $(TOOL_BUILD_SEGMENT) $(DEP_KERNAL) $(CFG_C64) $(GEN_STR_C64)
+$(DIR_MC64)/OUTK_x.BIN $(DIR_MC64)/KERNAL_combined.vs $(DIR_MC64)/KERNAL_combined.sym: \
+    $(TOOL_ASSEMBLER) $(TOOL_BUILD_SEGMENT) $(DEP_KERNAL) $(CFG_MC64) $(GEN_STR_MC64)
 $(DIR_GEN)/OUTK_x.BIN $(DIR_GEN)/KERNAL_combined.vs $(DIR_GEN)/KERNAL_combined.sym: \
    $(TOOL_ASSEMBLER) $(TOOL_BUILD_SEGMENT) $(DEP_KERNAL) $(CFG_GEN) $(GEN_STR_GEN)
 $(DIR_TST38)/OUTK_x.BIN $(DIR_TST38)/KERNAL_combined.vs $(DIR_TST38)/KERNAL_combined.sym: \
@@ -457,6 +468,7 @@ $(DIR_X16)/kernal.seg_1 $(DIR_X16)/KERNAL_1_combined.vs $(DIR_X16)/KERNAL_1_comb

 $(DIR_CUS)/OUTx_x.BIN:     $(DIR_CUS)/OUTB_x.BIN     $(DIR_CUS)/OUTK_x.BIN
 $(DIR_C64)/OUTx_x.BIN:     $(DIR_C64)/OUTB_x.BIN     $(DIR_C64)/OUTK_x.BIN
+$(DIR_MC64)/OUTx_x.BIN:    $(DIR_MC64)/OUTB_x.BIN    $(DIR_MC64)/OUTK_x.BIN
 $(DIR_GEN)/OUTx_x.BIN:     $(DIR_GEN)/OUTB_x.BIN     $(DIR_GEN)/OUTK_x.BIN
 $(DIR_GENCRT)/OUTx_0.BIN:  $(DIR_GENCRT)/OUTB_0.BIN  $(DIR_GENCRT)/OUTK_0.BIN
 $(DIR_TST38)/OUTx_x.BIN:   $(DIR_TST38)/OUTB_x.BIN   $(DIR_TST38)/OUTK_x.BIN
@@ -468,6 +480,7 @@ $(DIR_X16)/OUTx_0.BIN:     $(DIR_X16)/OUTB_0.BIN     $(DIR_X16)/OUTK_0.BIN

 $(TARGET_CUS_B):    $(DIR_CUS)/OUTx_x.BIN
 $(TARGET_C64_B):    $(DIR_C64)/OUTx_x.BIN
+$(TARGET_MC64_B):   $(DIR_MC64)/OUTx_x.BIN
 $(TARGET_GEN_B):    $(DIR_GEN)/OUTx_x.BIN
 $(TARGET_TST38_B):  $(DIR_TST38)/OUTx_x.BIN
 $(TARGET_TST60_B):  $(DIR_TST60)/OUTx_x.BIN
@@ -475,6 +488,7 @@ $(TARGET_U64_B):    $(DIR_U64)/OUTx_x.BIN

 $(TARGET_CUS_K):    $(DIR_CUS)/OUTx_x.BIN
 $(TARGET_C64_K):    $(DIR_C64)/OUTx_x.BIN
+$(TARGET_MC64_K):   $(DIR_MC64)/OUTx_x.BIN
 $(TARGET_GEN_K):    $(DIR_GEN)/OUTx_x.BIN
 $(TARGET_TST38_K):  $(DIR_TST38)/OUTx_x.BIN
 $(TARGET_TST60_K):  $(DIR_TST60)/OUTx_x.BIN
@@ -482,6 +496,7 @@ $(TARGET_U64_K):    $(DIR_U64)/OUTx_x.BIN

 build/symbols_custom.vs:          $(DIR_CUS)/BASIC_combined.vs       $(DIR_CUS)/KERNAL_combined.vs
 build/symbols_c64.vs:             $(DIR_C64)/BASIC_combined.vs       $(DIR_C64)/KERNAL_combined.vs
+build/symbols_mc64.vs:            $(DIR_MC64)/BASIC_combined.vs      $(DIR_MC64)/KERNAL_combined.vs
 build/symbols_generic.vs:         $(DIR_GEN)/BASIC_combined.vs       $(DIR_GEN)/KERNAL_combined.vs
 build/symbols_generic_crt.vs:     $(DIR_GENCRT)/BASIC_0_combined.vs  $(DIR_GENCRT)/KERNAL_0_combined.vs
 build/symbols_testing_38K.vs:     $(DIR_TST38)/BASIC_combined.vs     $(DIR_TST38)/KERNAL_combined.vs
@@ -499,6 +514,10 @@ $(GEN_STR_C64): $(TOOL_GENERATE_STRINGS) $(CFG_C64)
 	@mkdir -p $(DIR_C64)/,generated
 	$(TOOL_GENERATE_STRINGS) -o $@ -c $(CFG_C64)

+$(GEN_STR_MC64): $(TOOL_GENERATE_STRINGS) $(CFG_MC64)
+	@mkdir -p $(DIR_MC64)/,generated
+	$(TOOL_GENERATE_STRINGS) -o $@ -c $(CFG_MC64)
+
 $(GEN_STR_GEN): $(TOOL_GENERATE_STRINGS) $(CFG_GEN)
 	@mkdir -p $(DIR_GEN)/,generated
 	$(TOOL_GENERATE_STRINGS) -o $@ -c $(CFG_GEN)
@@ -541,6 +560,7 @@ build/,generated/,z80_tables.s: $(TOOL_GENERATE_Z80_TABLES)

 GEN_STR_custom         = $(GEN_STR_CUS)
 GEN_STR_c64            = $(GEN_STR_C64)
+GEN_STR_mc64           = $(GEN_STR_MC64)
 GEN_STR_generic        = $(GEN_STR_GEN)
 GEN_STR_generic_crt    = $(GEN_STR_GENCRT)
 GEN_STR_testing_38K    = $(GEN_STR_TST38)
@@ -0,0 +1,33 @@
+This is a modified version of MEGA65 Open ROMs (https://github.com/MEGA65/open-roms),
+forked at upstream commit ad178dbe4d48cd6a317737a8e0e7e662f7e33d32.
+
+Modified by Christian Werner, 2026-10-14 and 2026-10-15, for the mc64 computers of
+arnitech, a set of Minecraft mods (https://git.susdog.de/chris/arnitech). The fork lives
+at https://git.susdog.de/chris/open-roms, branch mc64.
+
+Changes:
+
+- src/,,config_mc64.s: a new build configuration, copied from src/,,config_c64.s, with its
+  own config ID ($6D), the brand "MC64", and BCD_SAFE_INTERRUPTS turned off.
+- Makefile: targets for that configuration, build/kernal_mc64.rom and build/basic_mc64.rom,
+  made the same way as the c64 ones.
+- src/kernal/iec/ciout.s (2026-10-15): CIOUT buffers its byte in TBTCNT, where the send
+  routine takes it from, not in BSOUR (upstream PR #113).
+- src/kernal/iec/close_iec.s (2026-10-15): CLOSE sends LISTEN, $E0 plus the secondary
+  address, and UNLISTEN; it sent a command ORed with zero page $E0 and no LISTEN.
+- src/kernal/iec/chkin_iec.s, ckout_iec.s (2026-10-15): CHKIN and CHKOUT take the secondary
+  address from SAT, not from LAT, the logical file numbers.
+- src/kernal/iec/tksa.s (2026-10-15): TKSA sends the secondary address it is given, without
+  ORing $90 into it (upstream issue #116).
+- src/kernal/iec/iec_tx_byte.s (2026-10-15): a data byte that no listener holds DATA for
+  sets ST to $80 (device not present) and returns, instead of waiting forever.
+- src/kernal/iec/close_iec.s (2026-10-15): a CLOSE that finds no device sets ST to $80
+  (device not present), and still frees the file number.
+- src/kernal/iec/unlsn.s, untlk.s (2026-10-15): UNLSN and UNTLK end with CLK, DATA, and ATN
+  released; UNLSN left CLK pulled, and UNTLK waited for a talker to pull CLK, which after
+  UNTALK none does, and then left CLK pulled.
+- src/kernal/iec/iec_return.s (2026-10-15): a serial routine that finds no device releases
+  CLK, DATA, and ATN; it left CLK pulled.
+- NOTICE: this file.
+
+The licence terms are unchanged; see LICENSE, COPYING, and COPYING.LESSER.
@@ -0,0 +1,130 @@
+
+;; #CONFIG# ID $6D ; should be 1 byte, different for each config file!
+
+;
+; Please read CONFIG.md before modifying this file!
+;
+
+; Idea:
+; The Firmware of arnitech's mc64 computers, a Minecraft mod
+; Same as the 'c64' configuration, except:
+; - the banner names mc64
+; - BCD_SAFE_INTERRUPTS is off, for IRQ entry timing closer to the original
+
+
+
+; --- Hardware platform and brand
+
+;; #CONFIG# PLATFORM_COMMODORE_64      YES
+;; #CONFIG# BRAND_CUSTOM               "MC64"
+
+
+; --- Processor instruction set
+
+;; #CONFIG# CPU_MOS_6502               YES
+;; #CONFIG# CPU_DTV_6502               NO
+;; #CONFIG# CPU_RCW_65C02              NO
+;; #CONFIG# CPU_WDC_65C02              NO
+;; #CONFIG# CPU_WDC_65816              NO
+;; #CONFIG# CPU_CSG_65CE02             NO
+
+
+; --- Memory model
+
+;; #CONFIG# MEMORY_MODEL_38K           YES
+;; #CONFIG# MEMORY_MODEL_46K           NO
+;; #CONFIG# MEMORY_MODEL_50K           NO
+;; #CONFIG# MEMORY_MODEL_60K           NO
+
+
+; --- IEC bus configuration
+
+;; #CONFIG# IEC                        YES
+;; #CONFIG# IEC_DOLPHINDOS             NO
+;; #CONFIG# IEC_DOLPHINDOS_FAST        NO
+;; #CONFIG# IEC_JIFFYDOS               NO
+;; #CONFIG# IEC_JIFFYDOS_BLANK         NO
+
+
+; --- Tape deck configuration
+
+;; #CONFIG# TAPE_NORMAL                YES
+;; #CONFIG# TAPE_TURBO                 NO
+;; #CONFIG# TAPE_AUTODETECT            NO
+;; #CONFIG# TAPE_NO_KEY_SENSE          NO
+;; #CONFIG# TAPE_NO_MOTOR_CONTROL      NO
+
+
+; --- Sound support
+
+;; #CONFIG# SID_2ND_ADDRESS            NO
+;; #CONFIG# SID_3RD_ADDRESS            NO
+;; #CONFIG# SID_D4XX                   NO
+;; #CONFIG# SID_D5XX                   NO
+;; #CONFIG# SID_D6XX                   NO
+;; #CONFIG# SID_D7XX                   NO
+
+
+; --- Keyboard settings
+
+;; #CONFIG# KEYBOARD_C128              NO
+;; #CONFIG# KEYBOARD_C128_CAPS_LOCK    NO
+;; #CONFIG# KEY_REPEAT_DEFAULT         NO
+;; #CONFIG# KEY_REPEAT_ALWAYS          NO
+;; #CONFIG# KEY_FAST_SCAN              YES
+;; #CONFIG# JOY1_CURSOR                YES
+;; #CONFIG# JOY2_CURSOR                YES
+
+;; #CONFIG# PROGRAMMABLE_KEYS          YES
+
+;; #CONFIG# KEYCMD_RUN                 "\5FL"
+
+;; #CONFIG# KEYCMD_F1                  "@8$"
+;; #CONFIG# KEYCMD_F2                  "LOAD"
+;; #CONFIG# KEYCMD_F3                  "@9$"
+;; #CONFIG# KEYCMD_F4                  "RUN:"
+;; #CONFIG# KEYCMD_F5                  "@10$"
+;; #CONFIG# KEYCMD_F6                  NO
+;; #CONFIG# KEYCMD_F7                  "@11$"
+;; #CONFIG# KEYCMD_F8                  NO
+
+;; #CONFIG# KEYCMD_HELP                "LIST"
+
+
+; --- Screen editor
+
+;; #CONFIG# EDIT_STOPQUOTE             YES
+
+
+; --- Software features
+
+;; #CONFIG# PANIC_SCREEN               YES
+;; #CONFIG# DOS_WEDGE                  NO
+;; #CONFIG# TAPE_WEDGE                 NO
+;; #CONFIG# TAPE_HEAD_ALIGN            NO
+;; #CONFIG# BCD_SAFE_INTERRUPTS        NO
+
+
+; --- BASIC features
+
+;; #CONFIG# ORIGINAL_UNPATCHED_BASIC   YES
+;; #CONFIG# TRANSCENDENTAL_FUNCTIONS   YES
+
+
+; --- Eye candy
+
+;; #CONFIG# COLORS_BRAND               NO
+;; #CONFIG# BANNER_SIMPLE              YES
+;; #CONFIG# BANNER_FANCY               NO
+;; #CONFIG# SHOW_FEATURES              YES
+
+
+; --- Debug options
+
+;; #CONFIG# DBG_STUBS_BRK              NO
+;; #CONFIG# DBG_PRINTF                 NO
+
+
+; --- Other
+
+;; #CONFIG# COMPRESSION_LVL_2          NO
@@ -14,7 +14,7 @@ chkin_iec:

 	; Fail if the file is open for writing (secondary address 1)
 	
-	lda LAT, Y
+	lda SAT, Y
 	cmp #$01
 	+beq chkin_file_not_input

@@ -24,7 +24,7 @@ chkin_iec:
 	jsr TALK
 	+bcs chkinout_device_not_present

-	lda LAT, Y
+	lda SAT, Y
 	ora #$60
 	jsr TKSA
 	+bcs chkinout_device_not_present
@@ -28,9 +28,10 @@ CIOUT:
 	
 ciout_store_in_buffer:

-	; Store in the buffer data to be sent next, return
+	; Store in the buffer data to be sent next, return; iec_tx_byte
+	; sends the byte from TBTCNT, so that is our buffer, not BSOUR
 	pla
-	sta BSOUR
+	sta TBTCNT
 	rts
 	
 ciout_send_byte:
@@ -14,7 +14,7 @@ ckout_iec:

 	; Fail if the file is open for reading (secondary address 0)
 	
-	lda LAT, Y
+	lda SAT, Y
 	+beq ckout_file_not_output

 	; Send LISTEN + SECOND first
@@ -23,7 +23,7 @@ ckout_iec:
 	jsr LISTEN
 	+bcs chkinout_device_not_present

-	lda LAT, Y
+	lda SAT, Y
 	ora #$60
 	jsr SECOND
 	+bcs chkinout_device_not_present
@@ -23,11 +23,23 @@ close_iec:
 	jsr iec_close_load 
 	jmp close_remove_from_table
@1:
-	ora $E0 ; CLOSE command
+	; LISTEN, CLOSE, UNLISTEN - see https://www.pagetable.com/?p=1031
+	lda FAT, y
+	jsr LISTEN
+	bcs close_iec_not_present
+	lda SAT, y
+	ora #$E0 ; CLOSE command
 	sta TBTCNT
 	jsr iec_tx_command
-	bcs close_iec_end
+	bcs close_iec_not_present
 	jsr iec_tx_command_finalize
+	jsr UNLSN
+	jmp close_remove_from_table
+
+close_iec_not_present:
+
+	; The file is closed all the same; READST says device not present
+	jsr kernalstatus_DEVICE_NOT_FOUND

 	; FALLTROUGH

@@ -36,8 +36,8 @@ iec_return_success:

 iec_return_DEVICE_NOT_FOUND:

-	; Set IEC line to normal idle state
-	jsr iec_set_idle
+	; Nobody answers: release all lines, so the bus is idle - see https://www.pagetable.com/?p=1135
+	jsr iec_release_atn_clk_data

 	; BSOUR is certainly not valid anymore
 	lda #$00
@@ -51,6 +51,17 @@ iec_tx_byte:
 	+phx_trash_a
 	+phy_trash_a

+	; A listener holds DATA until we release CLK; if nobody pulls it
+	; within 256us, no device is present - see https://www.pagetable.com/?p=1135
+	ldx #$18
+@0:
+	lda CIA2_PRA
+	bpl @1                             ; branch if DATA is pulled
+	dex
+	bne @0
+	jsr kernalstatus_DEVICE_NOT_FOUND
+	jmp iec_return_DEVICE_NOT_FOUND
+@1:
 	; Notify all devices that we are going to send a byte
 	; and it is going to be a data byte (released ATN)
 	jsr iec_release_atn_clk_data
@@ -28,8 +28,6 @@ TKSA:
 	; - https://www.lemon64.com/forum/viewtopic.php?t=57694&sid=531ba3592bcffadef2ac8b9162f2e529
 	; - https://www.pagetable.com/?p=1031 (Kernal API description)

-	ora #$90
-
 	jmp common_untlk_tksa

 } else {
@@ -42,7 +42,15 @@ UNLSN:
 	; Buffer empty, send the command
 	lda #$3F

-	jmp common_open_close_unlsn_second
+common_unlsn_untlk: ; common part of UNLSN and UNTLK
+
+	jsr common_open_close_unlsn_second
+	bcs @1
+
+	; The transmission is over: release CLK and DATA too, so the bus is idle - see https://www.pagetable.com/?p=1135
+	jmp iec_release_clk_data
+@1:
+	rts

 } else {

@@ -39,10 +39,11 @@ UNTLK:
 	sta IECPROTO
 }

-	; Buffer empty, send the command
+	; Buffer empty, send the command; the talker releases the bus - see https://www.pagetable.com/?p=1031
 	lda #$5F
+	jmp common_unlsn_untlk

-common_untlk_tksa: ; common part of UNTLK and TKSA
+common_untlk_tksa: ; the rest of TKSA

 	; XXX - for TKSA, is it really the right place to do a turnaround? I have some doubts
 	; (it forces us to send the TKSA command 'manually' sometimes), but
Author	SHA1	Message	Date
chris	0ec343a727	NOTICE: list the serial-bus fixes that leave the bus released	2026-10-15 14:21:36 +02:00
chris	729a410079	Serial bus: UNLSN, UNTLK, and a missing device leave the bus released UNLSN ended through iec_set_idle, which pulls CLK, so the C64 kept holding CLK after UNLISTEN. UNTLK waited for the talker to pull CLK, which no device does after UNTALK, timed out, and left CLK pulled with carry set. And a serial routine that found no device also left CLK pulled. A fastloader that waits for the drive to pull CLK after the KERNAL's UNLSN (Turrican's) then went on too early. The contract (Michael Steil, "Commodore Peripheral Bus: Part 4", https://www.pagetable.com/?p=1135): at the end of a transmission the sender releases CLK and the receivers release DATA, so the bus is idle again, and the controller releases ATN after each command; after UNTALK "the current talker will then release the bus" (Part 2, https://www.pagetable.com/?p=1031). UNLSN and UNTLK now share their end and release CLK and DATA; the device-not-present exit releases ATN, CLK, and DATA. Commodore's ROMs leave the same lines in the same scenarios, as differential tests in arnitech show. Not reported upstream (https://github.com/MEGA65/open-roms).	2026-10-15 14:21:36 +02:00
chris	7ee9d164e2	NOTICE: list the CLOSE fix for a device that does not answer	2026-10-15 02:50:48 +02:00
chris	51a2a43520	CLOSE: a device that does not answer sets ST to device not present When LISTEN or the CLOSE command found no device on the serial bus, close_iec freed the file number but left ST as it was, so READST after the CLOSE said 0. The contract: every device on the bus must answer ATN by pulling DATA, and when none does the result is DEVICE NOT PRESENT (Michael Steil, "Commodore Peripheral Bus: Part 2", https://www.pagetable.com/?p=1031); the C64 Programmer's Reference Guide's READST reports that as ST bit 7 ($80). close_iec now sets that bit when LISTEN or the CLOSE command fails, and still frees the file number. Commodore's ROMs give the same ST in the same scenario, as a differential test in arnitech shows. Not reported upstream (https://github.com/MEGA65/open-roms).	2026-10-15 02:50:48 +02:00
chris	ec7707d4cc	NOTICE: list the serial-bus fix for a byte with no listener	2026-10-15 02:32:03 +02:00
chris	74ef17d292	Serial bus: a data byte with no listener says DEVICE NOT PRESENT iec_tx_byte never checked that anyone was listening. With no listener, DATA stays released, so the wait for listeners to be ready returned at once, and a byte sent with EOI then waited forever for an EOI acknowledgement that never came. UNLSN, which sends the byte CIOUT holds back with EOI, hung the C64 after CHKOUT to a channel the drive refuses (DOS 2.6 leaves the bus when no write channel is open), or to a channel a CLOSE 15 has closed. The contract (Michael Steil, "Commodore Peripheral Bus: Part 4", https://www.pagetable.com/?p=1135): a listener holds DATA until the talker releases CLK; if at the beginning of a byte no receiver pulls DATA within 256 us, that is a DEVICE NOT PRESENT error. The C64 Programmer's Reference Guide's READST gives it as ST bit 7 ($80). iec_tx_byte now waits up to about 256 us for DATA to be pulled, and without it sets ST $80 and returns with DEVICE NOT PRESENT. Commodore's ROMs give the same ST in the same scenarios, as a differential test in arnitech shows. Not reported upstream (https://github.com/MEGA65/open-roms).	2026-10-15 02:31:56 +02:00
chris	b95a6ff057	NOTICE: list the serial-bus fixes of 2026-10-15 CIOUT's buffer, CLOSE's LISTEN/CLOSE/UNLISTEN, CHKIN's and CHKOUT's secondary address, and TKSA's secondary address.	2026-10-15 02:19:08 +02:00
chris	f1df180bf8	TKSA: send the secondary address the caller gives TKSA ORed the accumulator with $90 before sending it. Its callers pass the secondary address plus $60, as the routine's own comment asks, so TKSA turned a TALK secondary address $60-$6F into $F0-$FF, the OPEN command, on the bus. The contract (C64 Programmer's Reference Guide, TKSA; Michael Steil, "Commodore Peripheral Bus: Part 2", https://www.pagetable.com/?p=1031, which gives TKSA's argument as A = $60 + secondary address): TKSA sends the byte in A as the secondary address to the device told to TALK. TKSA now sends A as it is. Upstream: https://github.com/MEGA65/open-roms/issues/116 (bug 1)	2026-10-15 02:18:55 +02:00
chris	340bbefd06	CHKIN, CHKOUT: address the channel by the file's secondary address chkin_iec and ckout_iec read the secondary address from LAT, the table of logical file numbers, instead of SAT, the table of secondary addresses. A file whose number differed from its secondary address, such as OPEN 3,8,2, was read from or written to the wrong channel, and the read-only and write-only checks tested the file number. The contract (Michael Steil, "Commodore Peripheral Bus: Part 2", https://www.pagetable.com/?p=1031): CHKIN sends TALK and CHKOUT sends LISTEN, each followed by the secondary address OPEN was given; Compute!'s Mapping the Commodore 64 (p. 52) keeps the logical file numbers at $0259 (LAT) and the secondary addresses at $026D (SAT). Both routines now read SAT. Not reported upstream (https://github.com/MEGA65/open-roms); it may be what upstream issue #117's OPEN 1,8,0,"$" test met: https://github.com/MEGA65/open-roms/issues/117	2026-10-15 02:17:03 +02:00
chris	29124377fc	CLOSE: send LISTEN, CLOSE, UNLISTEN to a serial device close_iec sent its CLOSE command under ATN without first addressing the device with LISTEN and without UNLISTEN after it, and built the command with ORA $E0 (zero page) instead of ORA #$E0, so the byte it sent was the secondary address ORed with whatever $E0 held. The drive never learned of the CLOSE, so a file written on a channel was never written to the disk. The contract (Michael Steil, "Commodore Peripheral Bus: Part 2", https://www.pagetable.com/?p=1031): CLOSE of a file on a serial device sends LISTEN, then $E0 plus the secondary address, then UNLISTEN. close_iec now does that, as iec_close_load already does for LOAD. Not reported upstream (https://github.com/MEGA65/open-roms).	2026-10-15 02:15:38 +02:00
chris	264e9792a5	CIOUT: buffer the byte where iec_tx_byte sends it from CIOUT kept the byte to send next in BSOUR ($95), but iec_tx_byte, which CIOUT and iec_tx_flush (called by UNLSN, UNTLK, LISTEN, TALK) use to send it, transmits TBTCNT ($A4). So every byte CHROUT sent to a serial device was whatever TBTCNT held, and a file written with CHKOUT and CHROUT held the wrong bytes. The contract (C64 Programmer's Reference Guide, CIOUT): CIOUT sends a byte to the listening device, always holding one back so that the last byte goes with EOI when UNLSN ends the transfer. CIOUT now buffers the byte in TBTCNT, the one-line fix of upstream PR #113; changing the send path to read BSOUR would also move LOAD's and SAVE's bytes. Upstream: https://github.com/MEGA65/open-roms/pull/113	2026-10-15 02:15:38 +02:00
chris	840c5f1b61	Add the mc64 configuration, the Firmware of arnitech's mc64 A copy of the c64 configuration with its own ID ($6D), the brand "MC64", and BCD_SAFE_INTERRUPTS off, plus its Makefile targets build/kernal_mc64.rom and build/basic_mc64.rom, made the same way as the c64 ones. NOTICE says who modified the fork, when, and what changed.	2026-10-14 18:32:24 +02:00