PEEK & POKE Access to C64/C128 Memory

[RetrofanC]

Hi,

Also I am the proud owner of a OrangeCard.
Really a masterpiece of innovation from Marcus. ((-8

I am doing some baby steps but have some great idea's.
But I got already stuck with a c64/c128 memory PEEK.
Hopefully one of you can help me out.

I have the following simple test program.
Changing border colors and a pause loop.

Now the PEEK only works the 'first time'.
Meaning when I do a;

POKE 4096,0;

at the c64/c128 before I do the RVSYS$40000000

I do get the black border as first one and the @ sign at screen location $0500.
However, when the program is running in an endless while loop on the RISCV side.
I would have expected that when I do another;

POKE 4096,1;

at the c64/c128 side,
it will be picked up in one of the "while" cycles and changes the color to white and character at $0500 to A.

But that doesn't happen....... )-8

Only when I do;

POKE 4096,1;
RVSYS$40000000

The program starts again and shows the white border and A character as first one.

What is going wrong?

• Am I making a thinking mistake about the architecture?
• Do I need to add something to the c-code?

I also tried to use;
#define PEEK(addr) (*((const volatile uint8_t *)(void *)(addr)))
which doesn't make a difference.

I am sure it is something simple but I have tried a lot already and are just overlooking it.
So I thought lets check the community!
They might be able to point me in the right direction.... please..

=============================================================
#include <stdint.h>

#define PEEK(addr) (*((volatile uint8_t *)(void )(addr)))
#define POKE(addr,value) do{((volatile uint8_t *)(void *)(addr))=(value);}while(0)

void main(void)
{
volatile uint32_t count;
volatile uint8_t color;
color = 2;

while(1){
color = PEEK(0x1000);

for(count=0; count < 10000000;count++);
POKE(0xD020,color);
POKE(0x0500,color);

for(count=0; count < 10000000;count++);
POKE(0xD020,0x03);
POKE(0x0500,0x03);

for(count=0; count < 10000000;count++);
POKE(0xD020,0x04);
POKE(0x0500,0x04);

for(count=0; count < 10000000;count++);
POKE(0xD020,0x05);
POKE(0x0500,0x05);

for(count=0; count < 10000000;count++);
POKE(0xD020,0x06);
POKE(0x0500,0x06);

for(count=0; count < 10000000;count++);
POKE(0xD020,0x07);
POKE(0x0500,0x07);

for(count=0; count < 10000000;count++);
POKE(0xD020,0x08);
POKE(0x0500,0x08);

for(count=0; count < 10000000;count++);
}
for(;;);
}

[zeldin]

Because the C64 memory space is in the address range 0x0000-0xFFFF, it falls in the range covered by the RiscV core's data cache (any address with the MSB not set is cacheable in the simple setup used). Thus, once you read a value it will end up in the data cache, and stay there until that cache line gets evicted. The RVSYS command flushes both the data and instruction cache before starting the code, which is why re-issuing the RVSYS command fixes the problem for you.

You can use this macro to flush the data cache from inside your RiscV code:

#define CACHE_FLUSH() __asm__ __volatile__(".word 0x500F")

However, if you only want to pass some small message from the C64 side to the RiscV, a better option may be to use the mailbox area, which is uncached on the RiscV side. Please see the documentation for details.

[RetrofanC]

Brilliant, works like a charm now, thanks!