interrupts in camelforth

CamelForth in its current form has no facilities for handling interrupts, but it will co-exist with interrupts in the system (and they can use the CamelForth stack).

Here is an interrupt example. The code has two parts:

• An initialisation section that is invoked from CamelForth and which returns to CamelForth (an example of interacting politely with the CamelForth virtual machine (VM))
• An interrupt service routine -- all that it does is to use a memory location to count interrupts.

This code was written to test the mk2 memory mapping unit.

0001                         * TEST MULTICOMP TIMER INTERRUPT FROM CAMELFORTH
0002                         *
0003                         * 1/ NEED CAMELFORTH RUNNING FROM RAM SO THAT WE CAN CHANGE THE
0004                         * INTERRUPT VECTOR:
0005                         *    HEX MMUMAP EFTOCD E000 C000 2000 CMOVE CDTOCD PIVOTRST
0006                         * 2/ CHANGE VECTOR AT FFF8 TO POINT TO ISR
0007                         *    HEX 100F FFF8 !
0008                         * 3/ ENTER THIS CODE BELOW TO RAM @1000 (USE THE .LST FILE)
0009                         *    eg: 3606 1000 ! 8602 1002 ! (etc)
0010                         * 4/ RUN IT:
0011                         *    HEX 1000 EXECUTE
0012                         *
0013                         * SHOULD RETURN TO THE CAMELFORTH PROMPT IMMEDIATELY.
0014                         * INSPECT LOCATION "COUNT" - SHOULD SEE IT INCREMENTING AT 50Hz
0015                         * WRISTWATCH TEST: I SAW IT INCREMENT FROM 2665 TO 5679 IN
0016                         * 60s. (5679-2665)/50 = 60.28s
0017                         
0018 ffdd                    TIMER   EQU  $FFDD
0019                         
0020 1000                            ORG $1000
0021                         
0022                         * COME HERE FROM FORTH SO MUST PRESERVE FORTH VM: Y, D
0023                         * ENABLE TIMER AND INTERRUPT
0024 1000 36 06                       PSHU D
0025 1002 86 02                       LDA #2
0026 1004 b7 ff dd                    STA TIMER              START TIMER
0027 1007 1c ef                       ANDCC #%11101111       ENABLE INTERRUPTS
0028 1009 37 06                       PULU D
0029                         * RETURN TO CAMELFORTH
0030 100b 37 20                       PULU Y
0031 100d 6e b1                       JMP [,Y++]
0032                         
0033                         
0034                         * ISR - ALL REGISTERS SAVED/RESTORED ACROSS HERE
0035 100f 7c ff dd           ISR     INC TIMER
0036 1012 2a 08                      BPL NOTME
0037 1014 be 10 1d                   LDX COUNT
0038 1017 30 01                      LEAX 1,X            aka INX
0039 1019 bf 10 1d                   STX COUNT
0040                         NOTME
0041 101c 3b                         RTI
0042                         
0043 101d 00 00              COUNT   FDB $0
```