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 +1,127 @@
+; Writes Program Memory through the controller, and gets turned away from what it may
+; not touch.
+;
+; Writing code is the thing SplitBit's instruction set deliberately cannot do. The
+; controller can, which is what makes a loader possible. The marker below is written and
+; then read back through the controller, so the change is observed rather than assumed.
+;
+; The two refusals are the other half. Bank 2 is the bank table and is read only, so
+; writing to it is a GuardViolation. Bank 200 has nothing registered in it, so naming it
+; is a BankFault. Both handlers step the saved address past the instruction that was
+; refused, the way any handler carrying on past a fault has to.
+;
+; Correct output is:
+;   AA BB            the marker after being written through the controller
+;   readonly
+;   nobank
+;   done
+
+#Include print.asm
+
+#Program
+
+start:
+  ; Aim both ends of the controller at the marker.
+  SETD.0 Marker
+  PSHD.0
+  POPA
+  POPB
+  PSHA
+  PSHB
+
+  RSTA
+  OUTA 0xE0         ; SourceBank = 0
+  OUTA 0xE3         ; DestBank   = 0
+  POPB
+  OUTB 0xE1         ; SourceHigh
+  OUTB 0xE4         ; DestHigh
+  POPA
+  OUTA 0xE2         ; SourceLow
+  OUTA 0xE5         ; DestLow
+
+  ; Write two bytes over the marker. This is Program Memory being changed at run time.
+  INIA 0xAA
+  OUTA 0xE9
+  INIA 0xBB
+  OUTA 0xE9
+
+  ; Read them back the same way, to prove they landed.
+  CALL readAndPrint
+  CALL readAndPrint
+  CALL lineFeed
+
+  ; Bank 2 is the bank table, and it is read only.
+  INIA 0d2
+  OUTA 0xE3
+  RSTA
+  OUTA 0xE4
+  OUTA 0xE5
+  INIA 0d1
+  OUTA 0xE9         ; Refused: GuardViolation.
+
+  ; Bank 200 has nothing in it.
+  INIA 0d200
+  OUTA 0xE3
+  INIA 0d1
+  OUTA 0xE9         ; Refused: BankFault.
+
+  SETD.0 Done
+  CALL printString
+  CALL lineFeed
+  HALT
+
+readAndPrint:
+  INA 0xE9
+  CALL printByteHex
+  CALL blankSpace
+  RET
+
+readOnlyHandler:
+  SETD.0 ReadOnly
+  CALL printString
+  CALL lineFeed
+  BRI stepPastRefusal
+
+noBankHandler:
+  SETD.0 NoBank
+  CALL printString
+  CALL lineFeed
+  BRI stepPastRefusal
+
+; Steps the saved address past the refused instruction. OUT is two bytes, an opcode and
+; a port, so two is what it takes.
+stepPastRefusal:
+  MVSD.0
+  DPUP.0 0d14
+  LDA.0
+  CCF
+  INIB 0d2
+  ADD
+  MVQA
+  STA.0
+  BRC carried
+  RETI
+carried:
+  DPDN.0 0d01
+  LDA.0
+  INCA
+  STA.0
+  RETI
+
+; Never executed.
+Marker:
+  0x00 0x00
+
+#Data
+
+ReadOnly:
+"readonly"
+NoBank:
+"nobank"
+Done:
+"done"
+
+#Vectors
+
+  GuardViolation  readOnlyHandler
+  BankFault       noBankHandler