msx2: Further random guesswork as we go - memory sizing

diff --git a/Kernel/platform-msx2/main.c b/Kernel/platform-msx2/main.c
index 424870f..ee458e2 100644 (file)
--- a/Kernel/platform-msx2/main.c
+++ b/Kernel/platform-msx2/main.c
@@ -4,7 +4,10 @@
 #include <printf.h>
 #include <devtty.h>
 
-uint16_t vdpport = 0x98;
+/* These are set by the msx startup asm code */
+uint16_t vdpport;
+uint16_t infobits;
+uint16_t msxmaps;
 
 void platform_idle(void)
 {
@@ -24,7 +27,7 @@ void do_beep(void)
 
 void pagemap_init(void)
 {
-    int i = /*FIXME*/ 16; /* in 16K banks */
+    int i = msxmaps - 1;
     /* Add all the RAM, except 0,1,2,3 which is the kernel data/bss, add 0
        last to become the common for init */
     while (i > 3)

diff --git a/Kernel/platform-msx2/msx2.s b/Kernel/platform-msx2/msx2.s
index 99ab0b0..6a94bdc 100644 (file)
--- a/Kernel/platform-msx2/msx2.s
+++ b/Kernel/platform-msx2/msx2.s
@@ -25,6 +25,8 @@
             ; imported symbols
             .globl _ramsize
             .globl _procmem
+           .globl _msxmaps
+
             .globl _tty_inproc
             .globl unix_syscall_entry
             .globl trap_illegal
@@ -38,6 +40,10 @@
             .globl outstring
             .globl outstringhex
 
+           ; stuff to save
+           .globl _vdpport
+           .globl _infobits
+
             .include "kernel.def"
             .include "../kernel.def"
 
@@ -78,6 +84,15 @@ init_early:
             ret
 
 init_hardware:
+           ; save the useful bits of low memory first
+           ld hl, (0x2B)
+           ld (_infobits), a
+           ld a, (0x06)
+           ld (_vdpport), a
+
+           ; Size RAM
+           call size_memory
+
             ; set up interrupt vectors for the kernel mapped low page and
             ; data area
             ld hl, #0
@@ -95,6 +110,70 @@ init_hardware:
 
             .area _COMMONMEM
 
+;
+;      Called with interrupts off. See if we can work out how much RAM
+;      there is
+;
+size_memory:
+           ld bc, #0x04FC              ; bank 4, port 0xFC (MSX mapper)
+           ld hl, #8                   ; good a target as any
+           ld (hl), #0xAA              ; we know there is a low page!
+ramscan_2:
+           ld a, #0xAA
+ramscan:
+           out (c), b
+           cp (hl)                     ; is it 0xAA
+           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!
+ramwrapped:
+           ld a, #3
+           out (c), a
+           ld a, (hl)
+           ld (hl), #0x55
+           out (c), b
+           ld a, (hl)
+           cp #0x55
+           jr z, ramerror              ; Cool we wrapped both change to 0x55
+           ; Fluke RAM was 0xAA already
+           ld a, #3
+           out (c), a
+           ld a, #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)
+           ld a,#3
+           out (c), a          ; always put page 0 back
+
+           ;
+           ;   Address map back to normal so can update kernel data
+           ;
+
+           ld l, b
+           ld h, #0
+           ld a, l
+           or a                        ; zero count -> 256 pages
+           jr nz, pageslt256
+           inc h
+pageslt256:
+           ld (_msxmaps), hl
+           add hl, hl                  ; x 16 for Kb
+           add hl, hl
+           add hl, hl
+           add hl, hl
+
+           ; set system RAM size in KB
+           ld (_ramsize), hl
+           ld de, #0xFFC0
+           add hl, de          ; subtract 48K for the kernel
+           ld (_procmem), hl
+           ret
+
 _program_vectors:
             ; we are called, with interrupts disabled, by both newproc() and crt0
            ; will exit with interrupts off
@@ -108,6 +187,7 @@ _program_vectors:
            call map_process
 
             ; write zeroes across all vectors
+           ; on MSX this is probably the wrong thing to do!!! FIXME
             ld hl, #0
             ld de, #1
             ld bc, #0x007f ; program first 0x80 bytes only