2 ; Startup code for cc65 (CBM 600/700 version)
6 .export __STARTUP__ : absolute = 1 ; Mark as startup
8 .import callirq_y, initlib, donelib
9 .import push0, callmain
10 .import __BSS_RUN__, __BSS_SIZE__, __EXTZP_RUN__
11 .import __INTERRUPTOR_COUNT__
14 .include "zeropage.inc"
19 ; ------------------------------------------------------------------------
20 ; The BASIC header and a small BASIC program. Since it isn't possible to start
21 ; programs in other banks using SYS, the BASIC program will write a small
22 ; machine code program into memory at $100; and, start that machine code
23 ; program. The machine code program will then start the machine language
24 ; code in bank 1, which will initialize the system by copying stuff from
25 ; the system bank, and start the application.
27 ; Here's the BASIC program that's in the following lines:
34 ; 60 data 120,169,1,133,0
36 ; The machine program in the data lines is:
40 ; sta $00 <-- Switch to bank 1 after this command
42 ; Initialization is complex not only because of the jumping from one bank
43 ; into another. but also because we want to save memory; and because of
44 ; that, we will use the system memory ($00-$3FF) for initialization stuff
45 ; that is overwritten later.
50 .byte $03,$00,$11,$00,$0a,$00,$81,$20,$49,$b2,$30,$20,$a4,$20,$34,$00
51 .byte $19,$00,$14,$00,$87,$20,$4a,$00,$27,$00,$1e,$00,$97,$20,$32,$35
52 .byte $36,$aa,$49,$2c,$4a,$00,$2f,$00,$28,$00,$82,$20,$49,$00,$39,$00
53 .byte $32,$00,$9e,$20,$32,$35,$36,$00,$4f,$00,$3c,$00,$83,$20,$31,$32
54 .byte $30,$2c,$31,$36,$39,$2c,$31,$2c,$31,$33,$33,$2c,$30,$00,$00,$00
56 ;------------------------------------------------------------------------------
57 ; A table that contains values that must be transferred from the system zero-
58 ; page into our zero-page. Contains pairs of bytes, first one is the address
59 ; in the system ZP, second one is our ZP address. The table goes into page 2;
60 ; but, is declared here because it is needed earlier.
64 ; (We use .proc because we need both a label and a scope.)
77 ;------------------------------------------------------------------------------
78 ; Page 3 data. This page contains the break vector and the bankswitch
79 ; subroutine that is copied into high memory on startup. The space occupied by
80 ; this routine will later be used for a copy of the bank 15 stack. It must be
81 ; saved since we're going to destroy it when calling bank 15.
85 BRKVec: .addr _exit ; BRK indirect vector
89 excrts := $FF05 ; In bank 15 ROM
109 lda #.hibyte(excrts-1)
112 lda #.lobyte(excrts-1)
118 sta $1FF ; Save new sp
146 ldy $1FF ; Restore sp in bank 15
148 lda #.hibyte(expull-1)
151 lda #.lobyte(expull-1)
172 .if (expull <> $FF2E)
173 .error "Symbol expull must be aligned with Kernal in bank 15"
180 ;------------------------------------------------------------------------------
181 ; The code in the target bank when switching back will be put at the bottom
182 ; of the stack. We will jump here to switch segments. The range $F2..$FF is
183 ; not used by any Kernal routine.
189 ; We are at $100 now. The following snippet is a copy of the code that is poked
190 ; in the system bank memory by the BASIC header program; it's only for
191 ; documentation, and not actually used here:
197 ; This is the actual starting point of our code after switching banks for
198 ; startup. Beware: The following code will get overwritten as soon as we
199 ; use the stack (since it's in page 1)! We jump to another location since
200 ; we need some space for subroutines that aren't used later.
204 ; Hardware vectors, copied to $FFF6
210 .word nmi ; NMI vector
211 .word 0 ; Reset -- not used
212 .word irq ; IRQ vector
215 ; Initializers for the extended zero-page. See "extzp.s".
233 ; Switch the indirect segment to the system bank.
238 ; Initialize the extended zero-page.
240 ldx #.sizeof(extzp)-1
246 ; Save the old stack pointer from the system bank; and, set up our hw sp.
251 sta (sysp1),y ; Save system stack point into $F:$1FF
252 ldx #$FE ; Leave $1FF untouched for cross-bank calls
253 txs ; Set up our own stack
255 ; Copy stuff from the system zero-page to ours.
257 lda #.sizeof(transfer_table)
260 ldy transfer_table-2,x
261 lda transfer_table-1,x
269 ; Set the interrupt, NMI, and other vectors.
271 ldx #.sizeof(vectors)-1
273 sta $10000 - .sizeof(vectors),x
277 ; Set up the C stack.
279 lda #.lobyte(callbank15::entry)
281 lda #.hibyte(callbank15::entry)
284 ; Set up the subroutine and jump vector table that redirects Kernal calls to
287 ldy #.sizeof(callbank15)
288 @L1: lda callbank15-1,y
289 sta callbank15::entry-1,y
293 ; Set up the jump vector table. Y is zero on entry.
295 ldx #45-1 ; Number of vectors
296 @L2: lda #$20 ; JSR opcode
299 lda #.lobyte(callbank15::entry)
302 lda #.hibyte(callbank15::entry)
308 ; Set the indirect segment to the bank that we're executing in.
313 ; Zero the BSS segment. We will do that here instead of calling the routine
314 ; in the common library, since we have the memory anyway; and this way,
331 inc ptr1+1 ; Next page
335 ; Clear the remaining page.
337 Z2: ldx #<__BSS_SIZE__
345 ; ------------------------------------------------------------------------
346 ; We are at $200 now. We may now start calling subroutines safely since
347 ; the code we execute is no longer in the stack page.
351 ; Activate the chained interrupt handlers; then, enable interrupts.
353 Init: lda #.lobyte(__INTERRUPTOR_COUNT__*2)
357 ; Call module constructors.
361 ; Push the command-line arguments; and, call main().
365 ; Call the module destructors. This is also the exit() entry and the default entry
366 ; point for the break vector.
368 _exit: pha ; Save the return code
369 jsr donelib ; Run module destructors
371 sta irqcount ; Disable custom irq handlers
373 ; Address the system bank.
378 ; Copy stuff back from our zero-page to the system's.
381 lda #.sizeof(transfer_table)
384 ldy transfer_table-2,x
385 lda transfer_table-1,x
394 ; Place the program return code into BASIC's status variable.
400 ; Set up the welcome code at the stack bottom in the system bank.
403 lda (sysp1),y ; Load system bank sp
406 lda #$58 ; CLI opcode
409 lda #$60 ; RTS opcode
416 ; -------------------------------------------------------------------------
417 ; The IRQ handler goes into PAGE2. For performance reasons, and to allow
418 ; easier chaining, we do handle the IRQs in the execution bank (instead of
419 ; passing them to the system bank).
421 ; This is the mapping of the active IRQ register of the 6525 (tpi1):
423 ; Bit 7 6 5 4 3 2 1 0
425 ; | | | ^ SRQ IEEE 488
438 sta IndReg ; Be sure to address our segment
440 lda $105,x ; Get the flags from the stack
441 and #$10 ; Test break flag
448 ; Call the chained IRQ handlers.
452 jsr callirq_y ; Call the functions
454 ; Done with the chained IRQ handlers; check the TPI for IRQs, and handle them.
459 lda (tpi1),y ; Interrupt Register 6525
464 cmp #%00000001 ; ticker IRQ?
466 jsr scnkey ; Poll the keyboard
467 jsr UDTIM ; Bump the time
471 irqend: ldy #TPI::AIR
472 sta (tpi1),y ; Clear interrupt
485 ; -------------------------------------------------------------------------