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timer.go
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timer.go
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// This file is part of Gopher2600.
//
// Gopher2600 is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Gopher2600 is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Gopher2600. If not, see <https://www.gnu.org/licenses/>.
package arm7tdmi
import (
"fmt"
"github.com/jetsetilly/gopher2600/hardware/memory/cartridge/arm7tdmi/memorymodel"
)
type timer struct {
mmap memorymodel.Map
active bool
control uint32
counter float32
}
func (t *timer) stepFromVCS(armClock float32, vcsClock float32) {
if !t.active {
return
}
// the ARM timer ticks forward once every ARM cycle. the best we can do to
// accommodate this is to tick the counter forward by the the appropriate
// fraction every VCS cycle. Put another way: an NTSC spec VCS, for
// example, will tick forward every 58-59 ARM cycles.
t.counter += armClock / vcsClock
}
func (t *timer) step(cycles float32) {
if !t.active {
return
}
t.counter += cycles
}
func (t *timer) write(addr uint32, val uint32) (bool, string) {
var comment string
switch addr {
case t.mmap.TIMERcontrol:
t.control = val
t.active = t.control&0x01 == 0x01
if t.active {
comment = "timer on"
} else {
comment = "timer off"
}
case t.mmap.TIMERvalue:
t.counter = float32(val)
comment = fmt.Sprintf("timer = %d", val)
case t.mmap.TIMERprescale:
// not implemented yet
case t.mmap.TIMERprescaleMax:
// not implemented yet
case t.mmap.APBDIV:
// not implemented yet
default:
return false, comment
}
return true, comment
}
func (t *timer) read(addr uint32) (uint32, bool, string) {
var val uint32
var comment string
switch addr {
case t.mmap.TIMERcontrol:
val = t.control
case t.mmap.TIMERvalue:
val = uint32(t.counter)
comment = fmt.Sprintf("timer read = %d", val)
case t.mmap.TIMERprescale:
// not implemented yet
case t.mmap.TIMERprescaleMax:
// not implemented yet
case t.mmap.APBDIV:
// not implemented yet
default:
return 0, false, comment
}
return val, true, comment
}