some work towards I/O stack modularization

c64/,,config_generic.s

@@ -38,6 +38,13 @@
 // #define CONFIG_MEMORY_MODEL_60K
 
 
+// I/O devices
+
+#define CONFIG_IEC       // please keep enabled for now
+// #define CONFIG_TAPE   // please keep disabled for now
+// #define CONFIG_RS_232 // please keep disabled for now
+
+
 // Multiple SID support
 
 // #define CONFIG_SID_2ND

c64/,,config_mega65.s

@@ -40,6 +40,13 @@
 // #define CONFIG_MEMORY_MODEL_60K
 
 
+// I/O devices
+
+#define CONFIG_IEC       // please keep enabled for now
+// #define CONFIG_TAPE   // please keep disabled for now
+// #define CONFIG_RS_232 // please keep disabled for now
+
+
 // Multiple SID support
 
 #define CONFIG_SID_2ND

c64/,,config_testing.s

@@ -39,6 +39,13 @@
 #define CONFIG_MEMORY_MODEL_60K
 
 
+// I/O devices
+
+#define CONFIG_IEC       // please keep enabled for now
+// #define CONFIG_TAPE   // please keep disabled for now
+// #define CONFIG_RS_232 // please keep disabled for now
+
+
 // Multiple SID support
 
 #define CONFIG_SID_2ND

c64/,,config_ultimate64.s

@@ -38,6 +38,13 @@
 // #define CONFIG_MEMORY_MODEL_60K
 
 
+// I/O devices
+
+#define CONFIG_IEC       // please keep enabled for now
+// #define CONFIG_TAPE   // please keep disabled for now
+// #define CONFIG_RS_232 // please keep disabled for now
+
+
 // Multiple SID support
 
 // #define CONFIG_SID_2ND

c64/kernal/chkinout_real.s

@@ -39,6 +39,8 @@ chkin_real:
 	cmp #$01
 	beq chkinout_file_not_input
 
+#if CONFIG_IEC
+
 	// For IEC devices, send TALK + TKSA first
 	lda FAT,Y
 	jsr iec_check_devnum_oc
@@ -51,6 +53,8 @@ chkin_real:
 	jsr TKSA
 	bcs chkinout_device_not_present
 
+#endif // CONFIG_IEC
+
 chkin_set_device:
 	lda FAT,Y
 	sta DFLTN
@@ -121,6 +125,8 @@ ckout_real:
 	lda LAT, Y
 	beq chkinout_file_not_output
 
+#if CONFIG_IEC
+
 	// For IEC devices, send LISTEN + SECOND first
 	lda FAT,Y
 	jsr iec_check_devnum_oc
@@ -133,6 +139,8 @@ ckout_real:
 	jsr SECOND
 	bcs chkinout_device_not_present
 
+#endif // CONFIG_IEC
+
 chkout_set_device:
 	lda FAT,Y
 	sta DFLTO

c64/kernal/chrin_real.s

@@ -23,6 +23,8 @@ chrin_real:
 	beq chrin_keyboard // #$00 - keyboard
 	// XXX add screen support
 
+#if CONFIG_IEC
+
 	jsr iec_check_devnum_oc
 	bcc chrin_iec
 	jmp lvs_device_not_found_error // not a supported device
@@ -33,6 +35,8 @@ chrin_iec:
 	bcs chrin_done_fail
 	// FALLTROUGH
 
+#endif // CONFIG_IEC
+
 chrin_done:
 	clc // indicate success
 	rts

c64/kernal/iec/acptr.s

@@ -10,5 +10,11 @@
 
 
 ACPTR:
+
 	jsr kernalstatus_reset
+	
+#if CONFIG_IEC
 	jmp iec_rx_byte
+#else
+	jmp kernalerror_ILLEGAL_DEVICE_NUMBER
+#endif

c64/kernal/iec/close_iec.s

@@ -0,0 +1,35 @@
+
+//
+// IEC part of the CLOSE routine
+// 
+
+
+#if CONFIG_IEC
+
+
+// .Y contains LAT/FAT/SAT table index, it should stay this way
+
+close_iec:
+
+	jsr iec_tx_flush // make sure no byte is awaiting
+	lda SAT, y       // get secondary address
+	cmp #$60
+	bne !+
+
+	// workaround for using CLOSE on reading executable - XXX is this a proper way?
+	jsr iec_close_load 
+	jmp close_remove_from_table
+
+!:
+	ora $E0 // CLOSE command
+	sta TBTCNT
+	jsr iec_tx_command
+	bcs close_iec_end
+	jsr iec_tx_command_finalize
+
+close_iec_end:
+
+	jmp close_remove_from_table
+
+
+#endif // CONFIG_IEC

c64/kernal/iec/iec_check_devnum.s

@@ -6,26 +6,28 @@
 //
 
 
+#if CONFIG_IEC
+
 iec_check_devnum_lvs: // for load/verify/save
 
 	cmp #$08 // below 8 are illegal for load/save
-	bcs !+
+	bcc iec_check_devnum_failed
 
 	// FALLTROUGH
 
 iec_check_devnum_oc: // for open/close
 
 	cmp #$04 // below 4 are illegal, reserved for non-IEC devices on Commodore
-	bcs !+
+	bcc iec_check_devnum_failed
 
-	// FALLTROUGH
-
-iec_check_devnum_failed:
-	sec // indicate non-IEC device
-	rts
-
-!:
 	// 31 and above are illegal too, due to IEC command encoding scheme,
 	// see https://www.pagetable.com/?p=1031
 	cmp #$1F // sets carry for 31 or above
 	rts
+
+iec_check_devnum_failed:
+
+	sec // indicate non-IEC device
+	rts
+
+#endif // CONFIG_IEC

c64/kernal/iec/iec_close_load.s

@@ -1,8 +1,12 @@
 
+//
+// Common part of CLOSE and LOAD routines for IEC
+//
+
 
-// Common ppart of CLOSE and LOAD routines
+#if CONFIG_IEC
 
-close_load:
+iec_close_load:
 
 	tax
 
@@ -21,3 +25,5 @@ close_load:
 	jsr UNLSN
 
 	rts
+
+#endif // CONFIG_IEC

c64/kernal/iec/iec_cmd_close.s

@@ -5,6 +5,10 @@
 // - https://www.pagetable.com/?p=1031, https://github.com/mist64/cbmbus_doc
 //
 
+
+#if CONFIG_IEC
+
+
 iec_cmd_close:
 
 	jsr iec_check_channel_openclose
@@ -14,3 +18,6 @@ iec_cmd_close:
 	ora #$E0
 
 	jmp common_open_close_unlsn_second
+
+
+#endif // CONFIG_IEC

c64/kernal/iec/iec_cmd_open.s

@@ -6,6 +6,9 @@
 //
 
 
+#if CONFIG_IEC
+
+
 iec_cmd_open: // similar to TKSA, but without turnaround
 
 	jsr iec_check_channel_openclose
@@ -40,3 +43,6 @@ iec_check_channel_openclose:
 !:
 	clc // mark suitable channel number
 	rts
+
+
+#endif // CONFIG_IEC

c64/kernal/iec/iec_pull_atn_clk_release_data.s

@@ -1,4 +1,8 @@
 
+
+#if CONFIG_IEC
+
+
 iec_pull_atn_clk_release_data:
 
 	// Pulled CLK = DATA considered invalid; for extra robustness on non-emulated
@@ -13,3 +17,6 @@ iec_pull_atn_clk_release_data:
 	and #$FF - BIT_CIA2_PRA_DAT_OUT    // release
 	sta CIA2_PRA
 	rts
+
+
+#endif // CONFIG_IEC

c64/kernal/iec/iec_pull_clk_release_data.s

@@ -1,4 +1,8 @@
 
+
+#if CONFIG_IEC
+
+
 iec_pull_clk_release_data:
 
 	// Pulled CLK = DATA considered invalid; for extra robustness on non-emulated
@@ -11,3 +15,5 @@ iec_pull_clk_release_data:
 	and #$FF - BIT_CIA2_PRA_DAT_OUT    // release
 	sta CIA2_PRA
 	rts
+
+#endif // CONFIG_IEC

c64/kernal/iec/iec_pull_clk_release_data_oneshot.s

@@ -1,4 +1,8 @@
 
+
+#if CONFIG_IEC
+
+
 iec_pull_clk_release_data_oneshot:
 
 	lda CIA2_PRA
@@ -6,3 +10,6 @@ iec_pull_clk_release_data_oneshot:
 	and #$FF - BIT_CIA2_PRA_DAT_OUT    // release
 	sta CIA2_PRA
 	rts
+
+
+#endif // CONFIG_IEC

c64/kernal/iec/iec_pull_data_release_atn_clk.s

@@ -1,4 +1,8 @@
 
+
+#if CONFIG_IEC
+
+
 iec_pull_data_release_atn_clk:
 
 	// Released CLK = DATA considered valid; for extra robustness on non-emulated
@@ -13,3 +17,6 @@ iec_pull_data_release_atn_clk:
 	and #$FF - BIT_CIA2_PRA_ATN_OUT   // release
 	sta CIA2_PRA
 	rts
+
+
+#endif // CONFIG_IEC

c64/kernal/iec/iec_release_atn.s

@@ -1,4 +1,8 @@
 
+
+#if CONFIG_IEC
+
+
 iec_release_atn:
 
 	lda CIA2_PRA
@@ -6,3 +10,5 @@ iec_release_atn:
 	sta CIA2_PRA
 	rts
 
+
+#endif // CONFIG_IEC

c64/kernal/iec/iec_release_atn_clk_data.s

@@ -1,4 +1,8 @@
 
+
+#if CONFIG_IEC
+
+
 iec_release_atn_clk_data:
 
 	// Released CLK = DATA considered valid; for extra robustness on non-emulated
@@ -14,3 +18,5 @@ iec_release_atn_clk_data:
 	sta CIA2_PRA
 	rts
 
+
+#endif // CONFIG_IEC

c64/kernal/iec/iec_release_clk_data.s

@@ -1,4 +1,8 @@
 
+
+#if CONFIG_IEC
+
+
 iec_release_clk_data:
 
 	// Released CLK = DATA considered valid; for extra robustness on non-emulated
@@ -11,3 +15,6 @@ iec_release_clk_data:
 	and #$FF - BIT_CIA2_PRA_CLK_OUT    // release
 	sta CIA2_PRA
 	rts
+
+
+#endif // CONFIG_IEC

c64/kernal/iec/iec_release_clk_pull_data.s

@@ -1,4 +1,8 @@
 
+
+#if CONFIG_IEC
+
+
 iec_release_clk_pull_data:
 
 	// Released CLK = DATA considered valid; for extra robustness on non-emulated
@@ -11,3 +15,6 @@ iec_release_clk_pull_data:
 	and #$FF - BIT_CIA2_PRA_CLK_OUT    // release
 	sta CIA2_PRA
 	rts
+
+
+#endif // CONFIG_IEC

c64/kernal/iec/iec_return.s

@@ -8,6 +8,10 @@
 // take care about .A and IOSTATUS
 //
 
+
+#if CONFIG_IEC
+
+
 iec_return_success:
 
 	// BSOUR is certainly not valid anymore
@@ -32,3 +36,6 @@ iec_return_DEVICE_NOT_FOUND:
 	plx_trash_a
 	// Report error
 	jmp kernalerror_DEVICE_NOT_FOUND
+
+
+#endif // CONFIG_IEC

c64/kernal/iec/iec_rx_byte.s

@@ -4,6 +4,10 @@
 //
 // Preserves .X and .Y registers
 
+
+#if CONFIG_IEC
+
+
 iec_rx_byte:
 
 	// Store .X and .Y on the stack - preserve them
@@ -143,3 +147,5 @@ iec_rx_clk_wait2:
 	cli
 	rts
 
+
+#endif // CONFIG_IEC

c64/kernal/iec/iec_set_idle.s

@@ -1,7 +1,14 @@
 
+
+#if CONFIG_IEC
+
+
 iec_set_idle:
 	lda CIA2_PRA
 	ora #BIT_CIA2_PRA_CLK_OUT                                 // pull
 	and #$FF - BIT_CIA2_PRA_DAT_OUT - BIT_CIA2_PRA_ATN_OUT    // release
 	sta CIA2_PRA
 	rts
+
+
+#endif // CONFIG_IEC

c64/kernal/iec/iec_turnaround_to_listen.s

@@ -2,6 +2,10 @@
 // pages 7--8.
 // See also https://www.pagetable.com/?p=1135, https://github.com/mist64/cbmbus_doc
 
+
+#if CONFIG_IEC
+
+
 iec_turnaround_to_listen:
 
 	// Store .X and .Y on the stack - preserve them
@@ -34,3 +38,4 @@ iec_turnaround_to_listen:
 	jmp iec_return_success
 
 
+#endif // CONFIG_IEC

c64/kernal/iec/iec_turnaround_to_talk.s

@@ -2,6 +2,10 @@
 // pages 7--8.
 // See also https://www.pagetable.com/?p=1135, https://github.com/mist64/cbmbus_doc
 
+
+#if CONFIG_IEC
+
+
 iec_turnaround_to_talk:
 
 	// Store .X and .Y on the stack - preserve them
@@ -25,3 +29,5 @@ iec_turnaround_to_talk:
 	plp
 	jmp iec_return_success
 
+
+#endif // CONFIG_IEC

c64/kernal/iec/iec_tx_byte.s

@@ -7,6 +7,8 @@
 // Preserves .X and .Y registers
 
 
+#if CONFIG_IEC
+
 iec_tx_byte:
 
 	// Store .X and .Y on the stack - preserve them
@@ -94,3 +96,6 @@ iec_tx_common_bit_is_sent:
 	jmp iec_return_DEVICE_NOT_FOUND
 !:
 	jmp iec_return_success
+
+
+#endif // CONFIG_IEC

c64/kernal/iec/iec_tx_command.s

@@ -7,6 +7,9 @@
 // Preserves .X and .Y registers
 
 
+#if CONFIG_IEC
+
+
 iec_tx_command:
 
 	// Store .X and .Y on the stack - preserve them
@@ -36,3 +39,5 @@ iec_tx_command:
 	clc // Carry flag set is used for EOI mark
 	jmp iec_tx_common
 
+
+#endif // CONFIG_IEC

c64/kernal/iec/iec_tx_command_finalize.s

@@ -3,6 +3,9 @@
 // Implemented based on https://www.pagetable.com/?p=1135, https://github.com/mist64/cbmbus_doc
 
 
+#if CONFIG_IEC
+
+
 iec_tx_command_finalize:
 
 	// Store .X and .Y on the stack - preserve them
@@ -16,3 +19,6 @@ iec_tx_command_finalize:
 	jsr iec_wait20us
 
 	jmp iec_return_success
+
+
+#endif // CONFIG_IEC

c64/kernal/iec/iec_tx_flush.s

@@ -3,6 +3,10 @@
 //
 // Preserves .X, .Y and .A registers
 
+
+#if CONFIG_IEC
+
+
 iec_tx_flush:
 
 	pha
@@ -13,3 +17,6 @@ iec_tx_flush:
 !:
 	pla
 	rts
+
+
+#endif // CONFIG_IEC

c64/kernal/iec/iec_wait1ms.s

@@ -8,6 +8,9 @@
 // 63 cycles, we need at least 17 full rasters to be 100% sure we wait enough
 
 
+#if CONFIG_IEC
+
+
 iec_wait1ms:
 	ldx #18 // we probably won't start with the beginning of raster
 	lda VIC_RASTER
@@ -19,3 +22,6 @@ iec_wait1ms:
 	bne !-
 
 	rts
+
+
+#endif // CONFIG_IEC

c64/kernal/iec/iec_wait20us.s

@@ -1,4 +1,8 @@
 
+
+#if CONFIG_IEC
+
+
 iec_wait20us:
 
 	// Wait 20usec
@@ -20,3 +24,5 @@ iec_wait20us:
     //   1 cycle to fetch next instruction
     // ---
     //  21 cycles
+
+#endif // CONFIG_IEC

c64/kernal/iec/iec_wait60us.s

@@ -1,4 +1,8 @@
 
+
+#if CONFIG_IEC
+
+
 iec_wait60us:
 
 	// Wait 60usec
@@ -21,3 +25,5 @@ iec_wait60us:
     // ---
     //  64 cycles
 
+
+#endif // CONFIG_IEC

c64/kernal/iec/iec_wait_for_clk_release.s

@@ -1,7 +1,14 @@
 
+
+#if CONFIG_IEC
+
+
 iec_wait_for_clk_release:
 
 	lda CIA2_PRA
 	and #BIT_CIA2_PRA_CLK_IN
 	beq iec_wait_for_clk_release
 	rts
+
+
+#endif // CONFIG_IEC

c64/kernal/iec/iec_wait_for_data_pull.s

@@ -1,4 +1,8 @@
 
+
+#if CONFIG_IEC
+
+
 iec_wait_for_data_pull:
 
 	lda CIA2_PRA
@@ -6,3 +10,6 @@ iec_wait_for_data_pull:
 	// (highest bit set = negative value)
 	bmi iec_wait_for_data_pull
 	rts
+
+
+#endif // CONFIG_IEC

c64/kernal/iec/iec_wait_for_data_release.s

@@ -1,4 +1,8 @@
 
+
+#if CONFIG_IEC
+
+
 iec_wait_for_data_release:
 
 	lda CIA2_PRA
@@ -6,3 +10,5 @@ iec_wait_for_data_release:
 	// (highest bit set = negative value)
 	bpl iec_wait_for_data_release
 	rts
+
+#endif // CONFIG_IEC

c64/kernal/iec/listen.s

@@ -13,6 +13,8 @@
 
 LISTEN:
 
+#if CONFIG_IEC
+
 	// According to serial-bus.pdf (page 15) this routine flushes the IEC out buffer
 	jsr iec_tx_flush
 
@@ -25,3 +27,9 @@ LISTEN:
 	ora #$20
 
 	jmp common_talk_listen
+
+#else
+
+	jmp kernalerror_ILLEGAL_DEVICE_NUMBER
+
+#endif

c64/kernal/iec/load_iec.s

@@ -4,6 +4,9 @@
 //
 
 
+#if CONFIG_IEC
+
+
 load_iec_dev_not_found:
 	jmp lvs_device_not_found_error
 
@@ -94,7 +97,10 @@ iec_load_loop:
 	// Close file on drive
 
 	lda FA
-	jsr close_load
+	jsr iec_close_load
 
 	// Return last address
 	jmp lvs_return_last_address
+
+
+#endif // CONFIG_IEC

c64/kernal/iec/open_iec.s

@@ -0,0 +1,34 @@
+
+//
+// IEC part of the OPEN routine
+//
+
+
+#if CONFIG_IEC
+
+
+open_iec:
+
+	// We have a command to send to IEC device
+	jsr LISTEN
+	bcc !+
+	jmp kernalerror_DEVICE_NOT_FOUND
+!:
+	lda SA
+	jsr iec_cmd_open
+	bcc !+
+	jmp kernalerror_DEVICE_NOT_FOUND
+!:
+
+#if CONFIG_MEMORY_MODEL_60K
+	// We need our helpers to get to filenames under ROMs or IO area
+	jsr install_ram_routines
+#endif
+
+	// Send command ('file name')
+	jsr lvs_send_file_name
+
+	jmp open_done_success
+
+
+#endif // CONFIG_IEC

c64/kernal/iec/second.s

@@ -12,6 +12,8 @@
 
 SECOND:
 
+#if CONFIG_IEC
+
 	// Due to OPEN/CLOSE/TKSA/SECOND command encoding (see https://www.pagetable.com/?p=1031),
 	// allowed channels are 0-15; report error if out of range
 	cmp #$10
@@ -22,4 +24,8 @@ SECOND:
 
 	jmp common_open_close_unlsn_second
 
+#else
 
+	jmp kernalerror_ILLEGAL_DEVICE_NUMBER
+
+#endif

c64/kernal/iec/talk.s

@@ -13,6 +13,8 @@
 
 TALK:
 
+#if CONFIG_IEC
+
 	// According to serial-bus.pdf (page 15) this routine flushes the IEC out buffer
 	jsr iec_tx_flush
 
@@ -28,3 +30,9 @@ common_talk_listen: // common part of TALK and LISTEN
 
 	sta TBTCNT
 	jmp iec_tx_command
+
+#else
+
+	jmp kernalerror_ILLEGAL_DEVICE_NUMBER
+
+#endif

c64/kernal/iec/tksa.s

@@ -12,6 +12,8 @@
 
 TKSA:
 
+#if CONFIG_IEC
+
 	// Due to OPEN/CLOSE/TKSA/SECOND command encoding (see https://www.pagetable.com/?p=1031),
 	// allowed channels are 0-15; report error if out of range
 	cmp #$10
@@ -22,5 +24,8 @@ TKSA:
 
 	jmp common_untlk_tksa
 
+#else
 
+	jmp kernalerror_ILLEGAL_DEVICE_NUMBER
 
+#endif

c64/kernal/iec/unlsn.s

@@ -13,6 +13,8 @@
 
 UNLSN:
 
+#if CONFIG_IEC
+
 	// According to serial-bus.pdf (page 15) this routine flushes the IEC out buffer
 	jsr iec_tx_flush
 
@@ -21,5 +23,8 @@ UNLSN:
 
 	jmp common_open_close_unlsn_second
 
+#else
 
+	jmp kernalerror_ILLEGAL_DEVICE_NUMBER
 
+#endif

c64/kernal/iec/untlk.s

@@ -13,6 +13,8 @@
 
 UNTLK:
 
+#if CONFIG_IEC
+
 	// According to serial-bus.pdf (page 15) this routine flushes the IEC out buffer
 	jsr iec_tx_flush
 
@@ -31,3 +33,9 @@ common_untlk_tksa: // common part of UNTLK and TKSA
 	jmp iec_turnaround_to_listen
 !:
 	rts
+
+#else
+
+	jmp kernalerror_ILLEGAL_DEVICE_NUMBER
+
+#endif

c64/kernal/iostack/f291.close.s

@@ -16,30 +16,21 @@ CLOSE:
 	// Find the LAT / SAT / FAT entry which LAT corresponds to A
 
 	jsr find_fls
-	bcs close_error_not_found // XXX can we report error in IOSTATUS here?
+	bcs close_end // XXX can we report error in IOSTATUS here?
 
-	// We have the entry index in Y - check whether this is IEC device
+#if CONFIG_IEC
+
+	// We have the entry index in .Y - check whether this is IEC device
 	lda FAT, y
 	jsr iec_check_devnum_oc
-	bcs close_remove_from_table
+	bcc_far close_iec
 
-	// IEC device
+#endif // CONFIG_IEC
 
-	jsr iec_tx_flush // make sure no byte is awaiting
+	// FALLTROUGH
-	lda SAT, y       // get secondary address
-	cmp #$60
-	bne !+
-	// workaround for using CLOSE on reading executable - XXX is this a proper way?
-	jsr close_load 
-	jmp close_remove_from_table
-!:
-	ora $E0 // CLOSE command
-	sta TBTCNT
-	jsr iec_tx_command
-	bcs close_remove_from_table
-	jsr iec_tx_command_finalize
 
 close_remove_from_table:
+
 	// Remove channel from the table
 	iny
 	cpy #$0A
@@ -56,9 +47,6 @@ close_remove_from_table:
 	dec LDTND
 
 	clc // report success - not sure if original CLOSE does this, but it's nevertheless a good practice
-	rts
 
-close_error_not_found:
+close_end:
-
-	sec // report success - not sure if original CLOSE does this, but it's nevertheless a good practice
 	rts

c64/kernal/iostack/f34a.open.s

@@ -23,6 +23,7 @@ OPEN:
 	cmp LA
 	bne open_not_yet_open
 	jmp kernalerror_FILE_ALREADY_OPEN
+
 open_not_yet_open:
 	cpy #$00
 	jmp !-
@@ -60,33 +61,11 @@ open_has_space:
 	// Check for IEC device
 	lda FA
 	jsr iec_check_devnum_oc
-	bcc open_iec
+	bcc_far open_iec
 
 	// FALLTROUGH
+
 open_done_success:
 
 	clc
 	rts
-
-open_iec:
-
-	// We have a command to send to IEC device
-	jsr LISTEN
-	bcc !+
-	jmp kernalerror_DEVICE_NOT_FOUND
-!:
-	lda SA
-	jsr iec_cmd_open
-	bcc !+
-	jmp kernalerror_DEVICE_NOT_FOUND
-!:
-
-#if CONFIG_MEMORY_MODEL_60K
-	// We need our helpers to get to filenames under ROMs or IO area
-	jsr install_ram_routines
-#endif
-
-	// Send command ('file name')
-	jsr lvs_send_file_name
-
-	jmp open_done_success

c64/kernal/iostack/f4a5.load.s

@@ -40,15 +40,9 @@ LOAD:
 	// Check whether we support the requested device
 	lda FA
 
-	// Try IEC - legal device numbers for LOAD are 8-30
+#if CONFIG_IEC
-	// Device numbers above 30 can not be used as IEC (see https://www.pagetable.com/?p=1031),
+	jsr iec_check_devnum_lvs
-	// as the protocol combines device number with command code in one byte, above 30 it is
+	bcc_far load_iec
-	// no longer possible. Original ROMs show ILLEGAL DEVICE NUMBER error only for devices
+#endif // CONFIG_IEC
-	// 0-3; our implementation is more strict here
 
-	cmp #$1F
-	bcs !+              // >= 31  
-	cmp #$08
-	bcs_far load_iec    // >= 8
-!:
 	jmp lvs_illegal_device_number

c64/kernal/vector_real.s

@@ -12,8 +12,8 @@ vector_real:
 	// warning and does not mention any preparations needed.
 
 	// Initial idea was to do php, cli, ..., plp to make the routine safer,
-	// but it seems it might cause problem with initialization sequence,
+	// but it seems it might cause problem with initialization on XEMU emulator
-	// as the stack might be uninitialized when this routine is called
+	// XXX find out, why
 	
 	// Prepare the user data pointer - strange order to reduce risk
 	// of potential similarity to the original routine