small LOAD cleanup

c64/kernal/chkinout_real.s

@@ -41,7 +41,7 @@ chkin_real:
 
 	// For IEC devices, send TALK + TKSA first
 	lda FAT,Y
-	jsr iec_check_devnum
+	jsr iec_check_devnum_oc
 	bcs chkin_set_device
 	
 	jsr TALK
@@ -123,7 +123,7 @@ ckout_real:
 
 	// For IEC devices, send LISTEN + SECOND first
 	lda FAT,Y
-	jsr iec_check_devnum
+	jsr iec_check_devnum_oc
 	bcs chkout_set_device
 
 	jsr LISTEN

c64/kernal/chrin_real.s

@@ -23,7 +23,7 @@ chrin_real:
 	beq chrin_keyboard // #$00 - keyboard
 	// XXX add screen support
 
-	jsr iec_check_devnum
+	jsr iec_check_devnum_oc
 	bcc chrin_iec
 	jmp lvs_device_not_found_error // not a supported device
 

c64/kernal/clrchn_real.s

@@ -13,14 +13,14 @@ clrchn_real:
 
 	// Handle IEC input device
 	lda DFLTN
-	jsr iec_check_devnum
+	jsr iec_check_devnum_oc
 	bcs !+
 	// Previous device was IEC one - send UNTALK first
 	jsr UNTLK
 !:
 	// Restore output device to default
 	lda DFLTO
-	jsr iec_check_devnum
+	jsr iec_check_devnum_oc
 	bcs !+
 	// Handle IEC output device
 	jsr UNLSN

c64/kernal/f1ca.chrout.s

@@ -30,7 +30,7 @@ CHROUT:
 	bne !+
 	jmp chrout_screen
 !:
-	jsr iec_check_devnum
+	jsr iec_check_devnum_oc
 	bcs chrout_done_unknown_device // not a supported device
 
 chrout_iec:

c64/kernal/f291.close.s

@@ -20,7 +20,7 @@ CLOSE:
 
 	// We have the entry index in Y - check whether this is IEC device
 	lda FAT, y
-	jsr iec_check_devnum
+	jsr iec_check_devnum_oc
 	bcs close_remove_from_table
 
 	// IEC device

c64/kernal/f34a.open.s

@@ -59,7 +59,7 @@ open_has_space:
 	
 	// Check for IEC device
 	lda FA
-	jsr iec_check_devnum
+	jsr iec_check_devnum_oc
 	bcc open_iec
 
 	// FALLTROUGH

c64/kernal/f49e.load_int.s

@@ -1,13 +0,0 @@
-
-//
-// XXX Note: something unusual was done with LOAD routine - although the vector at $330 points to $F4A5,
-//           the Kernal jump table points to $F49E (see also Mapping the C64, page 76). By experimenting
-//           I have already discovered that $F4A5 performs indirect jump via ($0330) vector, but it must
-//           be doing a little bit more - not sure yet, what. Something similar is done with SAVE.
-//
-//           This has to be clarified.
-//
-
-LOAD_INT:
-    jmp (ILOAD)
-

c64/kernal/iec/iec_check_devnum.s

@@ -5,18 +5,27 @@
 // Preserves .A, .X and .Y
 //
 
-iec_check_devnum:
-	// 0, 1, 2, or 3 are illegal - reserved for non-IEC devices on Commodore
-	cmp #$04
+
+iec_check_devnum_lvs: // for load/verify/save
+
+	cmp #$08 // below 8 are illegal for load/save
 	bcs !+
+
 	// FALLTROUGH
+
+iec_check_devnum_oc: // for open/close
+
+	cmp #$04 // below 4 are illegal, reserved for non-IEC devices on Commodore
+	bcs !+
+
+	// 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
-	bcs iec_check_devnum_failed
-	// Carry is clear here - indicates IEC device
+	cmp #$1F // sets carry for 31 or above
 	rts

c64/kernal/iec/listen.s

@@ -17,7 +17,7 @@ LISTEN:
 	jsr iec_tx_flush
 
 	// Check whether device number is correct
-	jsr iec_check_devnum
+	jsr iec_check_devnum_oc
 	bcc !+
 	jmp kernalerror_DEVICE_NOT_FOUND
 !:
@@ -25,6 +25,3 @@ LISTEN:
 	ora #$20
 
 	jmp common_talk_listen
-
-
-

c64/kernal/iec/load_iec.s

@@ -1,60 +1,17 @@
+
 //
-// Official Kernal routine, described in:
-//
-// - [RG64] C64 Programmer's Reference Guide   - page 286
-// - [CM64] Compute's Mapping the Commodore 64 - page 231
-// - IEC reference at http://www.zimmers.net/anonftp/pub/cbm/programming/serial-bus.pdf
-//
-// CPU registers that has to be preserved (see [RG64]): none
+// IEC part of the LOAD routine
 //
 
 
-	// Expects that SETLFS and SETNAM are called before hand.
-	// $YYXX = load address.
-	// (ignored if SETLFS channel = 1, i.e., like ,8,1)
-	// If A=1 then VERIFY instead of LOAD.
-	// On exit, $YYXX is the highest address into which data
-	// will have been placed.
-
-	// XXX honor MSGFLG bit 6
-	// XXX add VERIFY support
-
-LOAD:
-
-	// Are we loading or verifying?
-	sta VERCKK
-
-	// Store start address of LOAD
-	stx STAL+0
-	sty STAL+1
-
-	// Reset status
-	jsr kernalstatus_reset
-
-#if CONFIG_MEMORY_MODEL_60K
-	// We need our helpers to get to filenames under ROMs or IO area
-	jsr install_ram_routines
-#endif
-
-	// Check whether we support the requested device
-	lda FA
-	and #$FC
-	bne !+
-	jmp lvs_illegal_device_number // device number below 4, not an IEC device
-!:
-	// Device numbers above 30 are also illegal (see https://www.pagetable.com/?p=1031),
-	// as the protocol combines device number with command code int one byte,
-	// above 30 it is no longer possible (UNLISTEN and UNTALK codes prevent using
-	// number 31), yet original ROMs show ILLEGAL DEVICE NUMBER error only
-	// for devices 0-3; in our implementation LISTEN / TALK will cause device
-	// not present detected for numbers above 30
+load_iec:
 
 	// Display SEARCHING FOR + filename
 	jsr lvs_display_searching_for
 
 	// http://www.zimmers.net/anonftp/pub/cbm/programming/serial-bus.pdf
-	// p13, 16; also p16 tells us this routine doesn't mess with the file table
-	// in the C64, only in the drive.
+	// p13, 16; also p16 tells us this routine does not mess with the file
+	// table in the C64, only in the drive.
 
 	// Call device to LISTEN (p16)
 	lda FA
@@ -111,7 +68,7 @@ LOAD:
 	// Display start address
 	jsr lvs_display_loading_verifying
 
-load_loop:
+iec_load_loop:
 	// We are now ready to receive bytes
 	jsr iec_rx_byte
 	bcc !+
@@ -130,7 +87,7 @@ load_loop:
 	// Check for EOI - if so, this was the last byte
 	lda IOSTATUS
 	and #K_STS_EOI
-	beq load_loop
+	beq iec_load_loop
 
 	// Display end address
 	jsr lvs_display_done

c64/kernal/iec/talk.s

@@ -17,7 +17,7 @@ TALK:
 	jsr iec_tx_flush
 
 	// Check whether device number is correct
-	jsr iec_check_devnum
+	jsr iec_check_devnum_oc
 	bcc !+
 	jmp kernalerror_DEVICE_NOT_FOUND
 !:
@@ -28,5 +28,3 @@ common_talk_listen: // common part of TALK and LISTEN
 
 	sta TBTCNT
 	jmp iec_tx_command
-
-

c64/kernal/iostack/f49e.load_int.s

@@ -0,0 +1,12 @@
+
+//
+// Note: Although the vector at $330 points to $F4A5, the Kernal jump table points to $F49E
+// (see also Mapping the C64, page 76). By experimenting I have discovered that $F49E performs
+// indirect jump via ($0330) vector, after setting MEMUSS.
+//
+
+LOAD_INT:
+
+	sty MEMUSS+1
+	stx MEMUSS+0
+    jmp (ILOAD)

c64/kernal/iostack/f4a5.load.s

@@ -0,0 +1,54 @@
+//
+// Official Kernal routine, described in:
+//
+// - [RG64] C64 Programmer's Reference Guide   - page 286
+// - [CM64] Compute's Mapping the Commodore 64 - page 231
+// - IEC reference at http://www.zimmers.net/anonftp/pub/cbm/programming/serial-bus.pdf
+//
+// CPU registers that has to be preserved (see [RG64]): none
+//
+
+
+	// Expects that SETLFS and SETNAM are called before hand.
+	// $YYXX = load address.
+	// (ignored if SETLFS channel = 1, i.e., like ,8,1)
+	// If A=1 then VERIFY instead of LOAD.
+	// On exit, $YYXX is the highest address into which data
+	// will have been placed.
+
+	// XXX add VERIFY support
+
+LOAD:
+
+	// Are we loading or verifying?
+	sta VERCKK
+
+	// Store start address of LOAD
+	lda MEMUSS+0
+	sta STAL+0
+	lda MEMUSS+1
+	sty STAL+1
+
+	// Reset status
+	jsr kernalstatus_reset
+
+#if CONFIG_MEMORY_MODEL_60K
+	// We need our helpers to get to filenames under ROMs or IO area
+	jsr install_ram_routines
+#endif
+
+	// Check whether we support the requested device
+	lda FA
+
+	// Try IEC - legal device numbers for LOAD are 8-30
+	// Device numbers above 30 can not be used as IEC (see https://www.pagetable.com/?p=1031),
+	// as the protocol combines device number with command code in one byte, above 30 it is
+	// no longer possible. Original ROMs show ILLEGAL DEVICE NUMBER error only for devices
+	// 0-3; our implementation is more strict here
+
+	cmp #$1F
+	bcs !+              // >= 31  
+	cmp #$08
+	bcs_far load_iec    // >= 8
+!:
+	jmp lvs_illegal_device_number