6502 wide stack

[valerio63]

Hello

I put a my old VHDL project of a wide (16 bit) stack 6502 CPU, also I added some useful opcodes for fast contest switch, zero page relocation etc.
The CPU has binary/decimal ALU for full compatibility, I tested this CPU on several projects (on Altera Cyclone IV) as intelligent I/O coprocessor for industrial automation projects for my company.
The clock cycles needed for opcodes are almost identical to original 6502 project, some opcode need less clock cycle than original CPU.

Best Regards
Valerio Venturi
Italy

[Dr Jefyll]

Welcome, Valerio

This is a nice selection of improvements. For example the exchange instructions appeal to me -- something so simple, but so worthwhile. It's almost like having new address modes. For example, if you want (ind),X mode then just use XYZ -- ie; exchange X with Y -- and follow up by using (ind),Y mode.

Maybe you can tell us more about that I/O coprocessor, please.

-- Jeff

Code: Select all

; new V6502 opcodes macros
phr:                .macro             ;AXY->SP: push A,X,Y to stack (useful for fast context switch) 
                    .byte        $8b
                    .endm
                    
plr:                .macro             ;SP->YXA: pull A,X,Y from stack (useful for fast context switch)
                    .byte        $ab
                    .endm

taz:                .macro             ;A->Z: copy A to zero page register (MSB base address)
                    .byte        $1b
                    .endm
                    
tza:                .macro             ;Z->A: copy zero page register to A
                    .byte        $3b
                    .endm

txy:                .macro             ;X->Y: copy X to Y
                    .byte        $9b
                    .endm
                    
tyx:                .macro             ;Y->X: copy Y to X 
                    .byte        $bb
                    .endm

xyx:                .macro             ;X<->Y: exchange X with Y 
                    .byte        $eb
                    .endm

xax:                .macro             ;A<->X: exchange A with X
                    .byte        $0b
                    .endm

xay:                .macro             ;A<->Y: exchange A with Y
                    .byte        $2b
                    .endm

isp:                .macro             ;X -> S (lsb); A -> S msb: copy X and A to S (16 bit stack pointer)
                    .byte        $4b
                    .endm

tsp:                .macro             ;S lsb -> X; S msb -> A: copy S to X and A 
                    .byte        $5b
                    .endm

                    
jsrx:               .macro       arg1  ;JSR ($XXXX,X) jump vector table indexed by X
                    .byte        $fc
                    .word        arg1
                    .endm

[valerio63]

Hello Jeff

I am sorry for delay to answer you but I was very busy, I used the V6502 as I/O coprocessor (or slave CPU) to help main CPU (PowerPC MPC5200) to execute several high speed tasks such intelligent DMA controller, several I2C and SPI interfaces, one CAN bus, incremental encoders, and some discrete I/Os, all of these devices was included in a large FPGA project. Also the ROM and SRAM for the V6502 was included in the FPGA and the main CPU could update "on fly" the software via a simple I2C bus. The main board project was a real time controller for robotic systems.
I choosed the 6502 due to his high deterministic architecture, and also for his speed to execute simple tasks, (the CPU clock was 50 MHZ and the preemptive multitasking interrupt ran at 10 KHZ, 100 microseconds per task).
Today the project is almost obsolete and we moved to a new ARM architecture.

-- Valerio

[barrym95838]

valerio63 wrote:

Today the project is almost obsolete and we moved to a new ARM architecture.

Thankfully, your robot didn't have an ego, because it would have taken a serious hit.

Mike B.

[valerio63]

.....the destiny of everyone (even the robots) is to become obsolete....

[valerio63]

Hello

i posted an example of multitasking source code for V6502

[valerio63]

I added a PDF file that shows the improvements of V6502

[BigEd]

Thanks!

As an aside, this note is interesting:

Quote:

Unlike 65C02 the RES input cannot be used as additional interrupt request signal...

We did discuss that here - it seems the early 'C02s did write to stack during reset, but the later 'C02s from WDC do not...

Having RTI pull the Z register could break some existing software, but I see why it's useful. A tradeoff!

[barrym95838]

Updated version here:

viewtopic.php?f=10&t=5026

Mike B.