84PCE:Ports:7000

Synopsis

Port Number: 7000-703F

Memory-mapped address: F20000

Function: General-Purpose Timers

This range provides three general-purpose 32-bit timers (appears to be model FTTMR010). They can count up or down, and run at either 32768Hz or the CPU clock speed. The counters can generate interrupts either when looping or when matching one of two customizable values. The OS uses the third timer when USB is connected.

Registers

All registers are little-endian and cross multiple 8-bit ports.

Timer 1	Timer 2	Timer 3	Bits, R/W?	Purpose	Description
7000 F20000	7010 F20010	7020 F20020	32-bit R/W	Counter register	Can be written directly, but it should be disabled first since the entire value cannot be written atomically.
7004 F20004	7014 F20014	7024 F20024	32-bit R/W	Reset value	The counter is reloaded with this value once it reaches 0.
7008 F20008	7018 F20018	7028 F20028	32-bit R/W	Match value 1	An interrupt will be generated when the counter matches this value.
700C F2000C	701C F2001C	702C F2002C	32-bit R/W	Match value 2	An interrupt will be generated when the counter matches this value.
7030 F20030	Same	Same	12-bit R/W	Control register
• Bit 0	• Bit 3	• Bit 6		Timer enable	Set to enable the corresponding timer.
• Bit 1	• Bit 4	• Bit 7		Clock source	Set 1 for 32768 Hz crystal, or 0 for CPU clock
• Bit 2	• Bit 5	• Bit 8		Interrupt enable	Set to generate an interrupt when the counter reaches 0.
• Bit 9	• Bit 10	• Bit 11		Count direction	Set to 1 to count up, or 0 to count down.
7034 F20034	Same	Same	12-bit R/W	Interrupt status	Reads the cause of the interrupt. Write 1 bits to reset.
• Bit 0	• Bit 3	• Bit 6		Match 1	Set after the counter reaches match register 1.
• Bit 1	• Bit 4	• Bit 7		Match 2	Set after the counter reaches match register 2.
• Bit 2	• Bit 5	• Bit 8		Overflow	Set after the counter reaches 0 and gets reloaded, but only if enabled in the control register.
7038 F20038	Same	Same	12-bit R/W	Interrupt mask?	Seems to have no effect on interrupt generation, despite being documented
7038 F20038			32-bit R	Revision number	Reads a constant 0x00010801, which corresponds to revision 1.8.1.