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bank.asm
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bank.asm
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MODULE Bank
prevPageA DEFB 0
prevPageB DEFB 0
userBank DEFB 0,0
pagesRequired DEFB 0
lastPageSize DEFW 0
pageA EQU MMU4_8000_NR_54
pageB EQU MMU5_A000_NR_55
;; NOTE: MMU3/5 are safe from being paged out when making
;; NextZXOS calls (unlike MMU0/1/6/7)
;; Note that although I'm blocking out 224 (potential) pages
;; the reality is that, even with a 2mb machine, that a good
;; number of these will already be reserved by the system.
poolSize EQU 224
;; TODO: add some protection for when in some future, there's a
;; 4mb spectrum next...
ALIGN 256
pool BLOCK poolSize,0
rolling DW pool ; use bank rolling by default for file saving
rollingActive DB 1
buffer EQU $8000
IFDEF TESTING
prevDebugPage DEFB 0
debugPage EQU MMU6_C000_NR_56
debug DW $C000
ENDIF
; C <- 16K bank number to use as active bank
; Modifies: A, BC (via macro)
init:
push bc
;; backup the banks that are sitting over $8000 and $A000
;; note that with a dot file, the stack originally is sitting at $FF42
;; so if I do use this area, I need to set my own stackTop
NextRegRead pageA ; loads A with pageA bank number
ld (prevPageA), a
NextRegRead pageB
ld (prevPageB), a
IFDEF TESTING
NextRegRead debugPage
ld (prevDebugPage), a
ld a, $28 ; debug is stored in first page of bank 20
nextreg debugPage, a
push bc
push de
push hl
;; erase 8K of the data in bank 20
ld bc, $2000
ld hl, debug
ld de, debug + 1
ld (hl), 0
ldir
pop hl
pop de
pop bc
ENDIF
pop bc
;; check the bank init method, `fileMode` = 0 if we're loading
;; data in and out of banks, and set to 1 if we're working with
;; files
ld a, (State.fileMode)
cp NOT_WRITING_TO_FILE
jr nz, .initNewBank
;; double the value as we'll get 16K bank
ld a, c
add a, a
ld (userBank), a
;; now page in our user banks
nextreg pageA, a ; set bank to A
inc a
nextreg pageB, a ; set bank to A
ret
.initNewBank
call allocateRollingBank
ret
erase:
ld bc, $4000 ; 16k
ld hl, buffer
ld de, buffer + 1
ld (hl), 0
ldir
ret
restore:
push af ; protect the F flags
;; only release the 2nd page if we're not testing - if we're
;; testing then this preserves 2nd part of bank 20
IFDEF TESTING
NextRegRead debugPage
call freePage
ld a, (prevDebugPage)
nextreg debugPage, a
ENDIF
ld a, (prevPageA)
nextreg pageA, a
ld a, (prevPageB)
nextreg pageB, a
;; if fileMode = 0 we're done, otherwise release the pages
ld a, (State.fileMode)
and a
jr z, .done
;; if writing to a file, we need to release the 2 pages we allocated
ld a, (userBank)
call freePage
.done
pop af
ret
;; via Matt Davies — 30/03/2021
; A <- 8k bank number
; Fc <- if out of memory
allocPage:
push ix
push bc
push de
push hl
; Allocate a page by using the OS function IDE_BANK.
ld hl,$0001 ; Select allocate function and allocate from normal memory.
call .callP3dos
ccf
ld a,e
pop hl
pop de
pop bc
pop ix
ret nc
xor a ; Out of memory, page # is 0 (i.e. error), CF = 1
scf
ret
.callP3dos:
exx ; Function parameters are switched to alternative registers.
ld de,IDE_BANK ; Choose the function.
ld c,7 ; We want RAM 7 swapped in when we run this function (so that the OS can run).
rst 8
db M_P3DOS ; Call the function, new page # is in E
ret
; E <- total pages available
; Modifies: HL
availablePages:
ld hl, $0004 ; ZX banks, available
call allocPage.callP3dos
ret
freePage:
push af
push ix
push bc
push de
push hl
ld e,a ; E = page #
ld hl,$0003 ; Deallocate function from normal memory
call allocPage.callP3dos
pop hl
pop de
pop bc
pop ix
pop af
ret
; Writes all the banks used in the rolling bank method to SD card all in one go
;
; Modifies: HL, BC, AF, DE, IX
flushBanksToDisk:
ld hl, pool
ld a, (pagesRequired)
ld d, a
;; this is a bit weird, but it ensures that we capture all the
;; pages to the sd card - in some cases we'll do a final write
;; of zero bytes to the storage (a waste of cpu cycles) but
;; this also simplifies logic and protects us from lossing the
;; last page of data.
inc d
.exactPageSize
ld a, d ; Now copy into A and other
ld b, a ; registers for loop prep
ld c, a
;; we allocate pages in pairs, so we need to make sure
;; we're releasing an even number of pages - so if A is odd
;; add 1 to the loop counter
bit 0, a
jr z, .loop
inc b
.loop
ld a, (hl)
nextreg pageA, a ; load page into $8000
ld (.SMC_pageNumber), a
push af
push bc
push hl
ld hl, buffer ; HL = starting point
;; if C = 0, then don't write
ld a, c
and a
jr z, .dealloc
;; if C == 1 then BC = Bank.lastPageSize
cp 1
jr z, .lastPage
ld bc, $2000
jr .write
.lastPage
ld bc, (Bank.lastPageSize)
.write
call Border
call esxDOS.fWrite
.dealloc
;; release the page - light version of freePage
.SMC_pageNumber EQU $+1
ld e, SMC ; E = page #
ld hl, $0003 ; Deallocate function from normal memory
call allocPage.callP3dos
pop hl
pop bc
pop af
inc l
dec c
djnz .loop
ret
deallocateAllRollingBanks:
ld hl, pool ; array of allocated pages
ld b, $ff
.loop
ld a, (hl)
and a
ret z ; if page is zero, we're done
push hl
push bc
ld e, a
ld hl, $0003 ; Deallocate function from normal memory
call allocPage.callP3dos
pop bc
pop hl
inc l ; point to next page in the array
djnz .loop
ret
; Allocates two 8K pages at a time then puts them in our MMU 4 & 5
;
; Modifies: HL, AF
allocateRollingBank:
ld hl, (rolling) ; HL = points to base of the pool
call allocPage
jr c, outOfMemory
ld (userBank), a
nextreg pageA, a
ld (hl), a
inc l
call allocPage
jr c, outOfMemory
ld (userBank), a
nextreg pageB, a ; set bank to A
ld (hl), a
inc l
ld (rolling), hl
ret
outOfMemory
call deallocateAllRollingBanks
ld hl, Err.outOfMemory
jp Error
ENDMODULE
; Not used directly - called from the NextRegRead macro
;
; A = register value
; A <- value of register
; Modifies: B
NextRegReadProc:
out (c), a
inc b
in a, (c)
ret