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 +1,66 @@
+; Reads Program Memory through the memory controller.
+;
+; Nothing on SplitBit could do this before. The CPU cannot reach its own code, which is
+; what a Harvard machine is, and this is the device that can.
+;
+; The bytes read back are a marker written into the Program Segment after the HALT, where
+; nothing executes them. The controller is aimed at it using the label's own address, so
+; this checks the controller against what the source says rather than against a guess
+; about where the assembler put things.
+;
+; The address steps on by itself, so reading a run of bytes is a loop over one
+; instruction rather than four.
+;
+; Correct output is:
+;   DE AD BE EF      the marker, read out of Program Memory
+;   01 FF            bank 0's record in bank 2: present, owned by the machine
+;   00 00            and its capacity, where zero means the whole 64K
+
+#Include print.asm
+
+#Program
+
+start:
+  ; Aim the controller at the marker, using the marker's own address.
+  SETD.0 Marker
+  PSHD.0            ; High byte, then low, so the low byte comes off first.
+  POPA
+  POPB
+  PSHA              ; Keep the low byte while A is needed for something else.
+
+  RSTA
+  OUTA 0xE0         ; SourceBank = 0, which is Program Memory.
+  OUTB 0xE1         ; SourceHigh
+  POPA
+  OUTA 0xE2         ; SourceLow
+
+  CALL readAndPrint
+  CALL readAndPrint
+  CALL readAndPrint
+  CALL readAndPrint
+  CALL lineFeed
+
+  ; Now the bank table, which is bank 2. Bank 0's record comes first.
+  INIA 0d2
+  OUTA 0xE0
+  RSTA
+  OUTA 0xE1
+  OUTA 0xE2
+
+  CALL readAndPrint     ; Flags: present.
+  CALL readAndPrint     ; Owner: the machine itself.
+  CALL lineFeed
+  CALL readAndPrint     ; Capacity, high byte.
+  CALL readAndPrint     ; Capacity, low byte.
+  CALL lineFeed
+  HALT
+
+readAndPrint:
+  INA 0xE9
+  CALL printByteHex
+  CALL blankSpace
+  RET
+
+; Never executed. It is here to be read rather than run.
+Marker:
+  0xDE 0xAD 0xBE 0xEF