Technical problem concerning the microcontroller of the RCX brick

I am a member of a project group at Aalborg University, Denmark, and the goal for our project on this semester is to code an operating system for the RCX brick from Lego.

During a whole week, I have been strugling with the 8 bit timers of the H8/3292 (which is a member of the H8/3297 series). I have in my hand section 9 of the hardware manual from Renesa (entitled "8-Bit Timers"), which should be enough to make the timers work. I had no problems making the 16 bit timer work using section 8 of the same manual. If someone is interested, my collections of links can found here:

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Let us jump right into the problem: I follow section 9 of the hardware manual to the letter, but I cannot make the 8 bit timerswork completely. I am able to set up one of channels, such that the overflow interrupt is requested on counter overflow, but when I try enabling either CMIA or CMIB (Compare-Match Interrupt Request A/B, done by setting bit 6/7 of the TCR, Timer Control Register) the brick fails to continue. I have tried executing my program in BrickEmu and on a real RCX brick - I get no error message from BrickEmu, and the RCX brick just ceases operation (it does not power off, just stops further execution). I know it is not a problem with my interrupt handler, because I used the same handler when I successfully enabled the "on-counter-overflow-interrupt-request".

I use these typedefs:

typedef unsigned char byte; typedef unsigned int word;

I use these defines:

// Timer Control Register #define C0_TCR *((volatile byte*)0xffc8) // Timer Control/Status Register #define C0_TCSR *((volatile byte*)0xffc9) // Time Constant Register A #define C0_TCORA *((volatile byte*)0xffca) // Serial/Timer Control Register #define C01_STCR *((volatile byte*)0xffc3) // Compare-Match A Interrupt Vector #define C0_CMIA *((volatile word*)0xfda8)

Here is my main function, which sets up channel 0 of the timer and "installs" the interrupt handler:

void _main(void) { // Make sure channel 0 of the timer is turned off C0_TCR = 0; // Set time constant register A to 100 // (this value is not important) C0_TCORA = 100; // Clear counter on compare-match A C0_TCR &= ~0x08; // Clear bit 3 C0_TCR |= 0x10; // Set bit 4 // Choose slowest internal clock source (Oe_p/1024) C0_TCR |= 0x03; // Set bit 0+1 C0_TCR &= ~0x04; // Clear bit 2 C01_STCR &= ~0x01; // Clear bit 0 // Make sure compare-match flag A is cleared C0_TCSR &= ~0x40; // Clear bit 6 // Set interrupt vector C0_CMIA = (word)&handler; // Enable compare-match interrupt request A C0_TCR |= 0x40; // Set bit 6 // Busy wait forever while (1); }

This is my interrupt handler:

void handler(void) { asm("push r0 \n\t" // Save registers "push r1 \n\t" // CCR and r6 are saved by ROM dispatcher "push r2 \n\t" "push r3 \n\t" "push r4 \n\t" "push r5 \n\t" "mov.w #0xf000, r0 \n\t" // Start motor A "bset #7, @r0 \n\t" "bclr #6, @r0 \n\t" "bclr #6, @0xc3:8 \n\t" // Clear CMFA (bit 6 of TCSR) "pop r5 \n\t" // Restore registers "pop r4 \n\t" "pop r3 \n\t" "pop r2 \n\t" "pop r1 \n\t" "pop r0" ); }

I expect motor A to start, when the interrupt is requested by the timer, but nothing happens.

Any help would be appreciated.

Best regards, Martin Toft