158 lines
4.1 KiB
C
158 lines
4.1 KiB
C
/* This file is included into vb.c and cannot be compiled on its own. */
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#ifdef VBAPI
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/***************************** Module Functions ******************************/
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/* Compute clocks until the next decrement to zero */
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static uint32_t tmrGetUntil(VB *sim) {
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uint32_t fullTick = sim->tmr.t_clk_sel ? 400 : 2000;
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uint32_t thisTick = sim->tmr.clocks +
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(sim->tmr.t_clk_sel ? 0 : 400 * (4 - sim->tmr.tick20));
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return thisTick + fullTick *
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(sim->tmr.counter == 0 ? sim->tmr.reload : sim->tmr.counter - 1);
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}
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/* Update the counter to a new value */
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static void tmrUpdate(VB *sim, uint16_t value) {
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if (value == 0 && sim->tmr.counter != 0) {
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if (sim->tmr.t_enb)
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sim->tmr.z_stat = 1;
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if (sim->tmr.tim_z_int)
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sim->cpu.irq |= 0x0002;
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}
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sim->tmr.counter = value;
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}
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/***************************** Library Functions *****************************/
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/* Process component */
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static void tmrEmulate(VB *sim, uint32_t clocks) {
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/* Process all clocks */
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for (;;) {
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/* Next tick is after time to process */
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if (sim->tmr.clocks > clocks) {
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sim->tmr.clocks -= clocks;
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sim->tmr.until -= clocks;
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return;
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}
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/* Advance forward the component's number of clocks */
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clocks -= sim->tmr.clocks;
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sim->tmr.until -= sim->tmr.clocks;
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sim->tmr.clocks = 400;
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sim->tmr.tick20 += sim->tmr.tick20 == 4 ? -4 : 1;
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/* Do not decrement counter */
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if (
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!sim->tmr.t_enb ||
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(!sim->tmr.t_clk_sel && sim->tmr.tick20 != 0)
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) continue;
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/* Advance to the next counter value */
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tmrUpdate(sim, sim->tmr.counter == 0 ?
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sim->tmr.reload : sim->tmr.counter - 1);
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if (sim->tmr.counter == 0)
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sim->tmr.until = tmrGetUntil(sim);
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}
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}
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/* Read a value from TCR */
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static int32_t tmrReadControl(VB *sim) {
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return 0xE4 |
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sim->tmr.t_clk_sel << 4 |
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sim->tmr.tim_z_int << 3 |
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sim->tmr.z_stat << 1 |
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sim->tmr.t_enb
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;
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}
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/* Simulate a hardware reset */
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static void tmrReset(VB *sim) {
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/* Normal */
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sim->tmr.t_enb = 0;
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sim->tmr.t_clk_sel = 0;
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sim->tmr.tim_z_int = 0;
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sim->tmr.z_stat = 0;
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/* Other */
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sim->tmr.clocks = 400;
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sim->tmr.counter = 0xFFFF;
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sim->tmr.reload = 0x0000;
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sim->tmr.tick20 = 0;
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}
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/* Determine how many clocks are guaranteed to process */
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static uint32_t tmrUntil(VB *sim, uint32_t clocks) {
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return sim->tmr.t_enb && sim->tmr.until < clocks ?
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sim->tmr.until : clocks;
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}
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/* Write a value to TCR */
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static void tmrWriteControl(VB *sim, uint8_t value) {
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/* Clear interrupt status */
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if (
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(value & 0x04) && /* Z-Stat-Clr */
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(
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!sim->tmr.t_enb ||
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(
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sim->tmr.counter != 0 &&
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!(value & 0x01) /* T-Enb */
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)
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)
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) {
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sim->tmr.z_stat = sim->tmr.counter != 0;
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sim->cpu.irq &= ~0x0002;
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}
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/* Hardware bug: decrement on switch to 20us mode */
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if (
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!sim->tmr.t_clk_sel &&
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(value & 0x10) && /* T-Clk-Sel */
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sim->tmr.tick20 != 4
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) {
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tmrUpdate(sim, sim->tmr.counter == 0 ?
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sim->tmr.reload : sim->tmr.counter - 1);
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}
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/* Parse fields */
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sim->tmr.t_clk_sel = value >> 4 & 1;
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sim->tmr.tim_z_int = value >> 3 & 1;
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sim->tmr.t_enb = value & 1;
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/* The interrupt is disabled */
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if (!sim->tmr.tim_z_int)
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sim->cpu.irq &= ~0x0002;
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/* Configure state */
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sim->tmr.until = tmrGetUntil(sim);
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/* TODO: Will Z-Stat raise an interrupt when Tim-Z-Int is set? */
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}
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/* Write to the high data register */
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static void tmrWriteHigh(VB *sim, uint8_t value) {
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sim->tmr.reload = (uint16_t) value << 8 | (sim->tmr.reload & 0x00FF);
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tmrUpdate(sim, sim->tmr.reload);
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sim->tmr.until = tmrGetUntil(sim);
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}
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/* Write to the low data register */
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static void tmrWriteLow(VB *sim, uint8_t value) {
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sim->tmr.reload = (sim->tmr.reload & 0xFF00) | value;
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tmrUpdate(sim, sim->tmr.reload);
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sim->tmr.until = tmrGetUntil(sim);
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}
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#endif /* VBAPI */
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