static INTERRUPT_GEN( assert_irq )
{
cpu_set_input_line(device, 0, ASSERT_LINE);
timer_set(device->machine, cpu_clocks_to_attotime(device, 14288), NULL, 0, clear_irq_cb);
/* Timing here is an educated GUESS, Z80 /INT must stay high so the irq
fires no less than TWICE per frame, else game doesn't work right.
6000000 / 56.747 = 105732.4616 cycles per frame, we'll call it A
screen size is 256x256, though less is visible.
lets assume we have 256 lines L and 40 'lines' (really line-times)
of vblank V:
So (A/(L+V))*V = the number of cycles spent in vblank.
(105732.4616 / (256+40)) * 40 = 14288.17049 z80 clocks in vblank
*/
}
static WRITE8_HANDLER( thunderx_1f98_w )
{
// logerror("%04x: 1f98_w %02x\n",cpu_get_pc(space->cpu),data);
/* bit 0 = enable char ROM reading through the video RAM */
K052109_set_RMRD_line((data & 0x01) ? ASSERT_LINE : CLEAR_LINE);
/* bit 1 = PMC-BK */
pmcbank = (data & 0x02) >> 1;
/* bit 2 = do collision detection when 0->1 */
if ((data & 4) && !(thunderx_1f98_data & 4))
{
calculate_collisions();
/* 100 cycle delay is arbitrary */
timer_set(space->machine, cpu_clocks_to_attotime(space->cpu,100), NULL, 0, thunderx_firq_callback);
}
thunderx_1f98_data = data;
}
