Differences

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--- timers [2024/09/23 17:51] – arisotura
+++ timers [2025/04/13 13:51] (current) – arisotura
@@ Line 3: / Line 3: @@
 The gamepad has the following timer registers: (TODO word better)
 ^ Address    ^ Desc. ^
+| 0xF0000400 | Prescaler for timer 0/1 |
+| 0xF0000404 | Prescaler for count-up timer |
+| 0xF0000408 | Count-up timer |
 | 0xF0000410 | Timer 0 control |
 | 0xF0000414 | Timer 0 counter |
 | 0xF0000418 | Timer 0 target  |
+| 0xF0000420 | Timer 1 control |
+| 0xF0000424 | Timer 1 counter |
+| 0xF0000428 | Timer 1 target  |
+===== Prescalers =====
+Registers 0xF0000400 and 0xF0000404 control the rate at which timers 0/1 and the count-up timer run, respectively.
+They are simple prescaler counters. For example, setting them to 63 will divide the input clock by 64.
+These registers are 8 bits wide.
+===== Count-up timer =====
+This is a simple timer that is always counting up. When writing a value to 0xF0000408, it will begin counting from the new value.
+This register is 32 bits wide.
@@ Line 17: / Line 38: @@
 | 0    | ?? |
 | 1    | Timer enable |
-| 4-6  | Prescaler? |
+| 2    | Count direction; 0=up, 1=down |
+| 4-6  | Prescaler |
+Bit0 is possibly used by firmware code but has no observable effect.
+Writing 0 to bit1 resets the timer to 0.
+The prescaler value has the following possible settings:
+^ Value ^ Frequency ^
+| 0     | Divide by 2 |
+| 1     | Divide by 4 |
+| 2     | Divide by 8 |
+| 3     | Divide by 16 |
+| 4     | Divide by 32 |
+| 5     | Divide by 64 |
+| 6     | Divide by 128 |
+| 7     | Divide by 256 |
 **0xF0000414**
-Counter. Can be written to, the timer will count from the new value.
+Counter. Can be written to, the timer will count from the new value. Writes are ignored when the timer isn't active.
-When the timer goes past the target, the timer is reloaded to 0 and IRQ 0x00 is triggered.
+When the timer goes past the target in count-up mode, or below zero in count-down mode, the timer is reloaded (to 0 in count-up mode, to the target value in count-down mode) and IRQ 0x00 is triggered.
 Writing a new value greater than the target does not cause a reload.
+This register is 32 bits wide.
@@ Line 33: / Line 72: @@
 Target.
-Before a reload, the last value the timer takes is equal to the target.
+In count-up mode, before a reload, the last value the timer takes is equal to the target. It is then reloaded to 0.
+In count-down mode, before a reload, the last value the timer takes is 0. It is then reloaded to the target value.
+===== Timer 1 =====
+Function identical to timer 0, except it triggers IRQ 0x01.