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changeset 22:06417341c50e
Add memory size detection (coco1/2) and rearrange variables some
Add memory size detection using the same algorithm used by the stock ROM,
but only do so for the Coco1/2. For the Coco3, just set an arbitrary top of
RAM just below the "ROM" area.
Also shift the line input buffer below the text screen just to keep
everything in one sequence.
| author | William Astle <lost@l-w.ca> |
|---|---|
| date | Wed, 09 Nov 2022 18:09:19 -0700 |
| parents | 2264569d7aca |
| children | 4b4806a32701 |
| files | src/lwbasic.s |
| diffstat | 1 files changed, 32 insertions(+), 2 deletions(-) [+] |
line wrap: on
line diff
--- a/src/lwbasic.s Tue Nov 08 22:29:47 2022 -0700 +++ b/src/lwbasic.s Wed Nov 09 18:09:19 2022 -0700 @@ -194,6 +194,7 @@ ; Start of memory which has the direct page and other data. org 0 dpstart equ * ; start of direct page +memtop rmb 2 ; absolute top of memory in 64K memory map readlinenoecho rmb 1 ; if nonzero, the readline routine won't echo its input rmb 0x71-* ; align RSTFLG/RSTVEC for stock ROM compatibility RSTFLG rmb 1 ; 0x55 if RSTVEC is valid @@ -217,10 +218,14 @@ FRQVEC rmb 3 ; FIRQ vector (for compatibility) keyb_state rmb 8 ; rollover table state keyb_buff rmb keyb_bufflen ; the keyboard ring buffer - rmb 0x200-* ; unused +linebuff rmb linebuffsize ; the line input buffer + ifne *&0x1ff + rmb 0x200-(*&0x1ff) + endc textscreen rmb 0x200 ; the actual text screen (must be on 512 byte alignment) -linebuff rmb linebuffsize ; the line input buffer +heapstart equ * ; start of dynamically allocated stuff org 0x8000 ; the hardware puts the ROMs here; it's not negotiable +ROMSTART equ * START orcc #0x50 ; make sure interrupts are disabled if we come here in an unusual way ifdef COCO3 ldu #gime_inite ; point to end of GIME initializer @@ -406,6 +411,31 @@ coldstart0 std ,x++ ; blank a couple of bytes cmpx #textscreen ; end of low memory? blo coldstart0 ; brif not + ifndef COCO3 +; This is the memory size detection sequence. This runs through memory starting at the bottom of memory +; and stops when it reaches something that can't be modified successfully. This is basically the same +; algorithm used by the stock ROM. It takes less space than doing a more pointed set of probes. The end +; result will be X pointing to the byte one below the top of RAM. This is intentional to ensure there +; is one writeable byte at the top of string space. Note that X will point to the byte after the end +; of the text screen when we get here. + ldx #heapstart ; point to start of heap +coldstart1 lda 2,x ; get original value at test location + coma ; invert all bits + sta 2,x ; write it to the memory location + cmpa 2,x ; did it take? + bne coldstart2 ; brif not + com 2,x ; restore memory byte + leax 1,x ; move pointer forward + bra coldstart1 ; go check next byte + else +; For the Coco3, we do not need to concern ourselves about where the top actual memory is so we don't +; bother doing a memory scan in the default 64K memory map. Because we always run from RAM, we can actually +; set the top of memory to the actual top of the 32K space without having to ensure there is an extra byte +; available above the string space. + ldx #ROMSTART-1 ; point to top of memory + endc +coldstart2 stx memtop ; save absolute top of memory + leas ,x ; put the stack there ldx #warmstart ; set up warm start handler stx RSTVEC lda #0x55 ; activate warm start handler