Memory controller implemented.

2026-08-15 20:43:53 -04:00
parent c4b2c27a2d
commit 04dfcd707b
32 changed files with 1842 additions and 21 deletions
@@ -0,0 +1,172 @@
+; The fence.
+;
+; A guarded range is a fence rather than a wall. Any program may raise one and any
+; program may lower it, so nobody is ever told no. What it stops is walking into
+; something by accident, which is the failure that costs an afternoon: without it, code
+; that gets walked over is found much later, when the wreckage is finally executed and
+; the evidence is long gone.
+;
+; The handler reads the controller's destination registers to say where the refused write
+; was aimed. That is the whole point of catching it at the instruction that did it: the
+; address is still sitting there to be read.
+;
+; The addresses here are absolute rather than labels, so that this says the same thing no
+; matter what else ends up in the Data Segment. Data Memory is 64K and this program uses
+; a hundred bytes of it, so 0x0200 is empty ground.
+;
+; Correct output is:
+;   outside ok        a write just below the fence went through
+;   caught 0200       a write inside it was refused, and the handler says where
+;   caught 01FC       a blit that merely clipped it was refused whole
+;   read ok           reading inside the fence is allowed: it guards writing
+;   lowered ok        after GuardOff the same write goes through
+;   fenced 05         the bank table shows bank 1 present and fenced
+
+#Include print.asm
+
+#Program
+
+start:
+  ; Fence off 0x0200 to 0x020F in Data Memory.
+  INIA 0d1
+  OUTA 0xEB             ; GuardBank = 1
+  INIA 0x02
+  OUTA 0xEC
+  RSTA
+  OUTA 0xED             ; GuardStart = 0x0200
+  INIA 0x02
+  OUTA 0xEE
+  INIA 0x0F
+  OUTA 0xEF             ; GuardEnd = 0x020F
+  INIA 0x10
+  OUTA 0xE8             ; GuardOn
+
+  ; Just below the fence is ordinary ground.
+  INIA 0x01
+  OUTA 0xE4
+  INIA 0xFF
+  OUTA 0xE5             ; Dest = 0x01FF
+  INIA 0d1
+  OUTA 0xE3             ; DestBank = 1
+  INIA 0x41
+  OUTA 0xE9
+  SETD.0 OutsideOk
+  CALL say
+
+  ; Inside it is not.
+  INIA 0x02
+  OUTA 0xE4
+  RSTA
+  OUTA 0xE5             ; Dest = 0x0200
+  INIA 0x42
+  OUTA 0xE9             ; Refused.
+
+  ; A blit from 0x01FC for eight bytes runs to 0x0203, so it clips the fence. It is
+  ; refused whole rather than doing the four bytes that would have fitted.
+  INIA 0x01
+  OUTA 0xE4
+  INIA 0xFC
+  OUTA 0xE5             ; Dest = 0x01FC
+  INIA 0d1
+  OUTA 0xE0
+  RSTA
+  OUTA 0xE1
+  OUTA 0xE2             ; Source = bank 1, 0x0000
+  OUTA 0xE6
+  INIA 0d8
+  OUTA 0xE7             ; Length = 8
+  INIA 0x01
+  OUTA 0xE8             ; Refused.
+
+  ; Reading inside a fence is allowed. A debugger has to be able to see what is being
+  ; protected.
+  INIA 0d1
+  OUTA 0xE0
+  INIA 0x02
+  OUTA 0xE1
+  RSTA
+  OUTA 0xE2             ; Source = 0x0200
+  INA 0xE9
+  SETD.0 ReadOk
+  CALL say
+
+  ; Lower it, and the write that was refused goes through.
+  INIA 0x11
+  OUTA 0xE8             ; GuardOff
+  INIA 0x02
+  OUTA 0xE4
+  RSTA
+  OUTA 0xE5
+  INIA 0x43
+  OUTA 0xE9
+  SETD.0 LoweredOk
+  CALL say
+
+  ; Raise it again, and read the flags back out of the bank table, where a fence is
+  ; published along with everything else about a bank.
+  INIA 0x10
+  OUTA 0xE8
+  INIA 0d2
+  OUTA 0xE0
+  RSTA
+  OUTA 0xE1
+  INIA 0d8
+  OUTA 0xE2             ; Bank 1's record begins at 8.
+  SETD.0 Fenced
+  CALL printString
+  CALL blankSpace
+  INA 0xE9
+  CALL printByteHex
+  CALL lineFeed
+  HALT
+
+; Says where the refused write was aimed, by reading the controller's own registers.
+guardHandler:
+  SETD.0 Caught
+  CALL printString
+  CALL blankSpace
+  INA 0xE4              ; DestHigh
+  CALL printByteHex
+  INA 0xE5              ; DestLow
+  CALL printByteHex
+  CALL lineFeed
+
+  ; Step past the refused instruction. Every write here is an opcode and a port.
+  MVSD.0
+  DPUP.0 0d14
+  LDA.0
+  CCF
+  INIB 0d2
+  ADD
+  MVQA
+  STA.0
+  BRC stepCarried
+  RETI
+stepCarried:
+  DPDN.0 0d01
+  LDA.0
+  INCA
+  STA.0
+  RETI
+
+say:
+  CALL printString
+  CALL lineFeed
+  RET
+
+#Data
+
+OutsideOk:
+"outside ok"
+Caught:
+"caught"
+ReadOk:
+"read ok"
+LoweredOk:
+"lowered ok"
+Fenced:
+"fenced"
+
+#Vectors
+
+  GuardViolation  guardHandler