Added CODE and DATA type headers, and using offsets for LDI and SVI. Not bothering with multitasking and context switching for now.

README.md

@@ -25,9 +25,9 @@ Completed:
 
 In progress:
 
-* context switching for simple multitasking
 * a unit test suite to ensure each instruction is correct
 * a proof-of-concept application
+* “simple” multitasking?
 
 The meat of the project:
 

common/Makefile

@@ -11,7 +11,7 @@ page6.obj: rom.h macros.h globals.h page6.src
 	xa -C -M page6.asm -l page6.lbl -o page6.obj
 
 globals.h: common.obj
-	grep -E -v '^(_|CMN_CD|CMN_DT|FN_FX)' common.lbl | sed -e 's/, 0, 0x0000//' -e 's/, / = /' -e 's/ 0x/ \x24/' > globals.h
+	grep -E -v '^(_|CMN_CD|CMN_DT|FN_FX|CODE|DATA)' common.lbl | sed -e 's/, 0, 0x0000//' -e 's/, / = /' -e 's/ 0x/ \x24/' > globals.h
 
 clean:
 	rm -f globals.h page6.asm common.obj page6.obj common.lbl page6.lbl system.obj

common/common.asm

@@ -2,6 +2,7 @@
 #include "common.h"
 
 	; ROM code header
+	.BYTE CODE
 	.WORD CMN_CD, _END_CMN_CD - CMN_CD
 
 	; beginning of ROM code
@@ -976,14 +977,13 @@ _CPR	.(		; CPR pq		0c pq		Rp <- Rq	- copy register
 
 _INILS	.(		; common initialization for LDI and SVI
 	JSR _CPYI1	; copy q to I1
-	CLC		; shift to get an address
-	ROR _I1+3
-	ROR _I1+2
-	ROR _I1+1
-	CLC
-	ROR _I1+3
-	ROR _I1+2
-	ROR _I1+1
+	CLC		; add the allocated memory offset
+	LDA _ARL
+	ADC _I1+1
+	STA _I1+1
+	LDA _ARH
+	ADC _I1+2
+	STA _I1+2
 	RTS
 .)
 
@@ -1054,6 +1054,7 @@ _3	ORA _F
 _END_CMN_CD
 
 	; ROM data header
+	.BYTE DATA
 	.WORD CMN_DT, _END_CMN_DT - CMN_DT
 
 	; beginning of ROM data
@@ -1071,6 +1072,7 @@ MNS_1	.BYTE $00, $fc, $ff, $ff
 _END_CMN_DT
 
 	; 6502 addresses
+	.BYTE DATA
 	.WORD ADDR, 6
 
 	; 6502 NMI, Reset and IRQ

common/common.h

@@ -46,9 +46,6 @@
 ; SVI pq		0e pq		(int(Rp)) <- Rq	- save indirect via allocated memory offset
 ; CMR pq		0f pq		F <- Rp <=> Rq	- compare registers
 
-; 32 bytes in page zero for memory map allocation
-_MAP	= _R0 - 256 / 8
-
 ; 40 bytes in page zero for common registers
 _R0	= $100 - 4 * (10 + 10)
 _R1	= _R0 + 4
@@ -69,8 +66,8 @@ _I3	= _I2 + 4
 _I4	= _I3 + 4
 _I5	= _I4 + 4
 _I6	= _I5 + 4			; register I6 maintains common status
-_I7	= _I6 + 4			; register I7 maintains locations of process and allocated memory
-_I8	= _I7 + 4			; register I8 maintains process information for context switching
+_I7	= _I6 + 4			; register I7 maintains locations of code and allocated memory
+_I8	= _I7 + 4			; register I8 is reserved for future use, e.g. context switching
 _I9	= _I8 + 4			; register I9 saves/restores processor status
 
 ; register I6 maintains common status
@@ -91,19 +88,15 @@ _F_N	=  32				; if Rr < 0.0 (after TST)
 _F_O	=  64				; if overflow (after arithmetic operations)
 _F_U	= 128				; if underflow (after arithmetic operations)
 
-; register I7 maintains locations of code and allocated real memory addresses
+; register I7 maintains locations of code and allocated memory
 _CRL	= _I7				; code low and high bytes
 _CRH	= _CRL + 1
 _ARL	= _CRH + 1			; allocated low and high bytes
 _ARH	= _ARL + 1
-_CR	= _CRL				; code real memory address
-_AR	= _ARL				; allocated real memory address
+_CR	= _CRL				; code memory address
+_AR	= _ARL				; allocated memory address
 
-; register I8 maintains process information for context switching
-_PSO	= _I8				; offset to running processes table
-_PSF	= _PSO + 1			; initial running process status PPPCCCLF
-_PST	= _PSF + 1			; current process status
-_PSI	= _PST + 1			; process stack index to save/restore
+; register I8 is reserved for future use, e.g. context switching
 
 ; register I9 saves/restores processor status
 ; (dd cc bb aa) aa: accumulator, bb: index X, cc: index Y, dd: processor status
@@ -116,31 +109,11 @@ _PS	= _IDY + 1			; saved processor status to restore
 
 ; using some of page two for register stack
 _RS	= $200				; register stack
-_RSS	= _R0				; register stack size
+_RSS	= FN_FX - _RS			; register stack size
 
-; for context switching, _R0 to _RS + _RSS - 1 needs to be saved and restored
-; this should comprise two pages or 512 bytes
+; system & user functions
 
-; the following are common process table and system & user functions
-
-; process information in the middle of page two
-_RP	= _RS + _RSS			; running processes table
-_RPS	= FN_FX - _RP			; running process table size
-
-; process information indices
-_RPV_I	= 0				; 4 bytes virtual memory address
-_RPR_I	= _RPV_I + 4			; 2 bytes real memory address
-_RPS_I	= _RPR_I + 2			; 1 byte size in pages: code + allocated memory + context switching
-_RPF_I	= _RPS_I + 1			; 1 byte status PPPCCCLF: P priority / C counter / L loaded / F finished
-
-; bits for status
-_S_L	=   1				; if program is loaded in memory
-_S_F	=   2				; if program is finished
-
-_RPE	= _RPF_I + 1			; size of running process entry
-_RPL	= _RPS / _RPE			; number of running processes limit
-
-; last 32 bytes of page two
+; 32 bytes at the end of page two
 FN_FX	= $300 - 2 * 16			; list of system and user functions
 
 ; function constants
@@ -183,4 +156,8 @@ _MSK_R	= %00111100			; mask for registers
 _MSK_T	= (_F_Z + _F_P + _F_N) ^ $ff	; mask for TST
 _MSK_C	= (_F_E + _F_G + _F_L) ^ $ff	; mask for CMP
 
+; section identifiers
+CODE	= %10101010			; to indicate CODE section
+DATA	= %01010101			; to indicate DATA section
+
 #endif /* __COMMON_H */

common/macros.h

@@ -78,7 +78,7 @@
 #define EXT(f)		.BYTE _EXT_C + (f)
 
 ; header, begin and end of blocks
-#define HDR(a)		.WORD a, _END_##a - a:* = * - 4:a .(
+#define HDR(t, a)	.BYTE t:.WORD a, _END_##a - a:* = * - 5:a .(
 #define BGN(a)		a .(
 #define END(a)		.):_END_##a
 

common/page6.src

@@ -4,12 +4,16 @@
 
 	* = $600
 
-HDR(DEMO)
+HDR(CODE, DEMO)
 	CMN
 	SET(R0, 9.4662)
+	SET(R1, 0)
+	SVI(R1, R0)
 	PSH(R0)
 	BRS(FACTORIAL)
 	POP(R4)
+	SET(R5, 0)
+	LDI(R6, R5)
 	ESC
 	BRK
 
@@ -29,4 +33,9 @@ END(FACTORIAL)
 
 END(DEMO)
 
-SVD_T	.BYTE 0, 0, 0, 0
+HDR(DATA, WORKING)
+
+ONE	.BYTE 0, 0, 0, 0
+TWO	.BYTE 0, 0, 0, 0
+
+END(WORKING)

emulator/main.c

@@ -7,6 +7,7 @@
 #define _R8	0xd0
 #define _I0	0xd8
 #define _I6	0xf0
+#define _I7	0xf4
 #define _I8	0xf8
 
 /* (dd cc bb aa) aa: index for register stack RS / ccbb: program counter PC / dd: flags F UONPZLGE */
@@ -16,6 +17,17 @@
 #define _F	_PCH + 1	/* flags */
 #define _PC	_PCL		/* program counter */
 
+/* register I7 maintains locations of code and allocated memory */
+#define _CRL	_I7				/* code low and high bytes */
+#define _CRH	_CRL + 1
+#define _ARL	_CRH + 1			/* allocated low and high bytes */
+#define _ARH	_ARL + 1
+#define _CR	_CRL				/* code memory address */
+#define _AR	_ARL				/* allocated memory address */
+
+#define CODE	0xaa				/* to indicate CODE section */
+#define DATA	0x55				/* to indicate DATA section */
+
 uint8_t memory[65536];
 
 uint8_t read6502(uint16_t address) {
@@ -48,22 +60,34 @@ void hook() {
 
 int main() {
 
-	uint8_t header[4];
+	uint8_t header[5];
 
 	while (fread(header, sizeof(header), 1, stdin))
 	{
-		uint16_t index = header[0] + (header[1] << 8);
-		uint16_t length = header[2] + (header[3] << 8);
+		uint8_t type = header[0];
+		uint16_t index = header[1] + (header[2] << 8);
+		uint16_t length = header[3] + (header[4] << 8);
 
-		printf("\n%04x %u\n", index, length);
+		printf("\n%x %04x %u\n", type, index, length);
 
 		if (fread(memory + index, length, 1, stdin))
 		{
-			memory[_PCL] = 	header[0];
-			memory[_PCH] = 	header[1];
+			switch (type) {
+				case CODE:
+					memory[_CRL] = 	header[1];
+					memory[_CRH] = 	header[2];
+					break;
+				case DATA:
+					memory[_ARL] = 	header[1];
+					memory[_ARH] = 	header[2];
+					break;
+			}
 		}
 	}
 
+	memory[_PCL] = 	memory[_CRL];
+	memory[_PCH] = 	memory[_CRH];
+
 	hookexternal(hook);
 
 	reset6502();