msx2: fix memory sizing

it was off by 3 pages

diff --git a/Kernel/platform-msx2/msx2.s b/Kernel/platform-msx2/msx2.s
index 04b7704..5da5342 100644 (file)
--- a/Kernel/platform-msx2/msx2.s
+++ b/Kernel/platform-msx2/msx2.s
@@ -141,25 +141,26 @@ init_hardware:
             .area _COMMONMEM
 
 ;
-;      Called with interrupts off. See if we can work out how much RAM
-;      there is
+; Size currently selected memory mapper
 ;
 size_memory:
-           ld bc, #0x04FC              ; bank 4, port 0xFC (MSX mapper)
+           ld bc, #0x03FC              ; make sure ram page 3 is selected
+           out (c), b
            ld hl, #8                   ; good a target as any
            ld (hl), #0xAA              ; we know there is a low page!
+           ld bc, #0x04FC              ; continue with page 4
 ramscan_2:
            ld a, #0xAA
 ramscan:
            out (c), b
            cp (hl)                     ; is it 0xAA
-           jr z, ramwrapped    ; we've wrapped (hopefully)
+           jr z, ramwrapped            ; we've wrapped (hopefully)
            ld (hl), a
            cp (hl)
            jr nz, ramerror             ; ermm.. help ???
            inc b
            jr nz, ramscan
-           jr ramerror         ; not an error we *could* have 256 pages!
+           jr ramerror                 ; not an error we *could* have 256 pages!
 ramwrapped:
            ld a, #3
            out (c), a
@@ -172,17 +173,18 @@ ramwrapped:
            ld a, #3
            out (c), a
            ld a, #0xAA
-           ld (hl), a          ; put the marker back as 0xAA
+           ld (hl), a                  ; put the marker back as 0xAA
            inc b
            jr nz, ramscan_2            ; Continue our memory walk
-ramerror:                              ; Ok so there are 256-b pages of 16K)
+ramerror:                              ; Ok so there are 256-b-3 pages of 16K)
            ld a,#3
-           out (c), a          ; always put page 0 back
-
+           out (c), a                  ; always put page 0 back
            ;
            ;   Address map back to normal so can update kernel data
            ;
-
+           dec b                       ; take into account we started at page 3
+           dec b
+           dec b
            ld l, b
            ld h, #0
            ld a, l
@@ -199,7 +201,7 @@ pageslt256:
            ; set system RAM size in KB
            ld (_ramsize), hl
            ld de, #0xFFD0
-           add hl, de          ; subtract 48K for the kernel
+           add hl, de                  ; subtract 48K for the kernel
            ld (_procmem), hl
            ret
 
@@ -433,9 +435,9 @@ map_savearea:
 map_kernel_data:
            .db 3,2,1,4
 _slotrom:
-        .db 0
+           .db 0
 _slotram:
-        .db 0
+           .db 0
 
 ; emulator debug port for now
 outchar: