bank94: not yet in use or tested

Initial pieces to support the use of 0x94 as the secondary bank control
register as used by some of the TRS80 expansions.

diff --git a/Kernel/platform-trs80/trs80-bank94.s b/Kernel/platform-trs80/trs80-bank94.s
new file mode 100644 (file)
index 0000000..f3bc3a2
--- /dev/null
+++ b/Kernel/platform-trs80/trs80-bank94.s
@@ -0,0 +1,247 @@
+;
+;          TRS 80 banking logic for the base Model 4 and 4P with
+;          the port 0x94 banking extensions.
+;
+
+            .module trs80bank
+
+            ; exported symbols
+            .globl init_hardware
+           .globl map_kernel
+           .globl map_process
+           .globl map_process_a
+           .globl map_process_always
+           .globl map_save
+           .globl map_restore
+           .globl _opreg
+           .globl _modout
+
+            ; imported symbols
+           .globl _program_vectors     
+            .globl _ramsize
+            .globl _procmem
+           .globl _nbanks
+
+           .globl s__COMMONMEM
+           .globl l__COMMONMEM
+
+            .include "kernel.def"
+            .include "../kernel.def"
+
+; -----------------------------------------------------------------------------
+; KERNEL MEMORY BANK (below 0xE800, only accessible when the kernel is mapped)
+; -----------------------------------------------------------------------------
+            .area _CODE
+
+init_hardware:
+           call detect94
+           or a
+           jr z, extended_system
+            ; set system RAM size
+            ld hl, #128
+extended_system:
+            ld (_ramsize), hl
+           ld de, #64          ; for kernel
+           or a
+           sbc hl, de
+            ld (_procmem), hl
+
+            ; set up interrupt vectors for the kernel (also sets up common memory in page 0x000F which is unused)
+            ld hl, #0
+            push hl
+            call _program_vectors
+            pop hl
+
+            im 1 ; set CPU interrupt mode
+
+           ; interrupt mask
+           ; 60Hz timer on
+
+           ld a, #0x24         ; 0x20 for serial
+           out (0xe0), a
+            ret
+
+
+;------------------------------------------------------------------------------
+; COMMON MEMORY PROCEDURES FOLLOW
+
+            .area _COMMONMEM
+
+opsave:            .db 0x06    ; used as a word so keep together
+save94:            .db 0x01
+_opreg:            .db 0x06    ; kernel map, 80 columns
+_modout:    .db 0x50   ; 80 column, sound enabled, altchars off,
+                       ; external I/O enabled, 4MHz
+_mirror94:  .db 0x01   ; mirror of 0x94 port
+
+detect94:
+;
+;      This will spot 0x94 bank switches eventually. For now report none
+;
+           ld a, (_opreg)
+           and #0x8C
+           or #0x73
+           out (_opreg), a
+           xor a
+           out (0x94), a
+;
+;      If we have 0x94 banking then the the low 32K is a mirror of the high
+;      32K
+;
+           ld hl, #0x800
+           ld a, (0x8800)
+           cp (hl)
+           jr nz, nobank94
+;
+;      Could be the same could be luck.
+;
+           inc (hl)
+           ld a, (0x8800)
+           cp (hl)
+           jr nz, nobank64_f1
+           dec (hl)
+;
+;      Seems we have banking extensions present
+;
+;      Write 0xA5 into a fixed location in all banks but zero
+;
+;      For each bank check the byte selected is A5 and write the bank into
+;      it. When we see a bank not reporting A5 we have found the wrap.
+;
+           ld a, #0xA5
+           ld bc, #0x3f94
+markall:
+           out (c), b
+           ld (hl), a
+           djnz markall
+
+scanall:    inc b
+           bit 6, a
+           jr nz, scandone
+           out (c), b
+           cp (hl)             ; Still A5 ?
+           jr nz, scandone
+           ld (hl), b
+           jr scanall
+scandone:
+           ld a, b
+           ld (_nbanks), a
+           xor a
+           ; B is the first bank we don't have, 0 based, so B is number of
+           ; 64K banks we found (max 32)
+           srl b       ; BA *= 64
+           rra
+           srl b
+           rr a
+           ld l, a     ; Report size in HL
+           ld h, b
+           ret
+           
+           
+nobank64_f1
+           dec (hl)
+nobank64:
+           xor a
+           ld h, a
+           ld l, #128          ; We ought to check/abort on a 64K box ?
+           ret    
+;
+;      Mapping set up for the TRS80 4/4P
+;
+;      The top 32K bank holds kernel code and pieces of common memory
+;      The lower 32K is switched between the various user banks and the
+;      base kernel bank
+;
+map_kernel:
+           push af
+           ld a, (_opreg)
+           and #0x8C           ; keep video bits
+           or #0x02            ; map 2, base memory
+           ld (_opreg), a
+           out (0x84), a       ; base memory so 0x94 doesn't matter
+           pop af
+           ret
+;
+;      Userspace mapping is mode 3, U64K/L32 mapped at L64K/L32
+;      Mapping codes 0x63 / 0x73. 0x94 on a bank expanded TRS80 then
+;      selects how the upper bank decodes
+;
+map_process:
+           ld a, h
+           or l
+           jr z, map_kernel
+map_process_hl:
+           ld a, (_opreg)
+           and #0x8C
+           or #0x63
+           bit 7, (hl)         ; low or high ?
+           jr z, maplo
+           or #0x10
+maplo:
+           ld (_opreg), a
+           out (0x84), a
+           ld a, (hl)
+           and #0x3F
+           ret z               ; not using bank94
+           ld (_mirror94), a
+           out (0x94), a
+           ret
+
+map_process_a:                 ; used by bankfork
+           push af
+           push bc
+           ld b, a
+           ld a, (_opreg)
+           and #0x8C
+           or #0x63
+           bit 7, b
+           jr z, maplo2
+           or #0x10
+maplo2:
+           ld (_opreg), a
+           out (0x84), a
+           ld a, b
+           and #0x3f
+           jr z, nobank94      ; zero means no bank94 hw present
+           ld (_mirror94), a
+           out (0x94), a
+nobank94:
+           pop bc
+           pop af
+           ret
+
+map_process_always:
+           push af
+           push hl
+           ld hl, #U_DATA__U_PAGE
+           call map_process_hl
+           pop hl
+           pop af
+           ret
+
+map_save:   push af
+           ld a, (_opreg)
+           and #0x73
+           ld (opsave), a
+           ld a, (_mirror94)
+           ld (save94), a
+           pop af
+           ret
+
+map_restore:
+           push af
+           push bc
+           ld bc, (opsave)             ; c = opsave b = save94
+           ld a, (_opreg)
+           and #0x8C
+           or c
+           ld (_opreg), a
+           out (0x84), a
+           ld a, b
+           and #0x3f
+           jr z, norestore94
+           out (0x94), a
+norestore94:
+           pop bc
+           pop af
+           ret