shrooms-vb-core/core/timer.c

131 lines
3.3 KiB
C

/* This file is included into vb.c and cannot be compiled on its own. */
#ifdef VBAPI
/***************************** Module Functions ******************************/
/* Update the counter to a new value */
static void tmrUpdate(VB *sim, uint16_t value) {
if (value == 0 && sim->tmr.counter != 0) {
if (sim->tmr.t_enb)
sim->tmr.z_stat = 1;
if (sim->tmr.tim_z_int)
sim->cpu.irq |= 0x0002;
}
sim->tmr.counter = value;
}
/***************************** Library Functions *****************************/
/* Process component */
static void tmrEmulate(VB *sim, uint32_t clocks) {
/* Timer is disabled */
if (!sim->tmr.t_enb)
return;
/* Process all clocks */
for (;;) {
/* Next tick is after time to process */
if (sim->tmr.clocks > clocks) {
sim->tmr.clocks -= clocks;
sim->tmr.until -= clocks;
return;
}
/* Advance forward the component's number of clocks */
clocks -= sim->tmr.clocks;
sim->tmr.until -= sim->tmr.clocks;
sim->tmr.clocks = sim->tmr.t_clk_sel ? 400 : 2000;
/* Advance to the next counter value */
tmrUpdate(sim, sim->tmr.counter == 0 ?
sim->tmr.reload : sim->tmr.counter - 1);
if (sim->tmr.counter == 0)
sim->tmr.until = sim->tmr.clocks * ((uint32_t)sim->tmr.reload + 1);
}
}
/* Read a value from TCR */
static int32_t tmrReadControl(VB *sim) {
return 0xE4 |
sim->tmr.t_clk_sel << 4 |
sim->tmr.tim_z_int << 3 |
sim->tmr.z_stat << 1 |
sim->tmr.t_enb
;
}
/* Simulate a hardware reset */
static void tmrReset(VB *sim) {
/* Normal */
sim->tmr.t_enb = 0;
sim->tmr.t_clk_sel = 0;
sim->tmr.tim_z_int = 0;
sim->tmr.z_stat = 0;
/* Other */
sim->tmr.counter = 0xFFFF;
sim->tmr.reload = 0x0000;
}
/* Determine how many clocks are guaranteed to process */
static uint32_t tmrUntil(VB *sim, uint32_t clocks) {
return sim->tmr.t_enb && sim->tmr.until < clocks ?
sim->tmr.until : clocks;
}
/* Write a value to TCR */
static void tmrWriteControl(VB *sim, uint8_t value) {
/* Clear interrupt status */
if (
(value & 0x04) && /* Z-Stat-Clr */
(
sim->tmr.counter != 0 ||
!sim->tmr.t_enb
)
) {
sim->tmr.z_stat = sim->tmr.counter != 0;
sim->cpu.irq &= ~0x0002;
}
/* Parse fields */
sim->tmr.t_clk_sel = value >> 4 & 1;
sim->tmr.tim_z_int = value >> 3 & 1;
sim->tmr.t_enb = value & 1;
/* The interrupt is disabled */
if (!sim->tmr.tim_z_int)
sim->cpu.irq &= ~0x0002;
/* Configure countdowns */
sim->tmr.clocks = sim->tmr.t_clk_sel ? 400 : 2000;
sim->tmr.until = sim->tmr.clocks * (sim->tmr.counter == 0 ?
(uint32_t) sim->tmr.reload + 1 : sim->tmr.counter);
/* TODO: Will Z-Stat raise an interrupt when Tim-Z-Int is set? */
}
/* Write to the high data register */
static void tmrWriteHigh(VB *sim, uint8_t value) {
sim->tmr.reload = (uint16_t) value << 8 | (sim->tmr.reload & 0x00FF);
tmrUpdate(sim, sim->tmr.reload);
}
/* Write to the low data register */
static void tmrWriteLow(VB *sim, uint8_t value) {
sim->tmr.reload = (sim->tmr.reload & 0xFF00) | value;
tmrUpdate(sim, sim->tmr.reload);
}
#endif /* VBAPI */