lan9311 Standard Microsystems Corp., lan9311 Datasheet - Page 162

• Manufacturer Part Number: lan9311
• Description: Lan9311/lan9311i Two Port 10/100 Managed Ethernet Switch With 16-bit Non-pci Cpu Interface
• Manufacturer: Standard Microsystems Corp.

Chapter 12 General Purpose Timer & Free-Running Clock
Revision 1.2 (04-08-08)
12.1
12.2
This chapter details the LAN9311/LAN9311i General Purpose Timer (GPT) and the Free-Running
Clock.
The LAN9311/LAN9311i provides a 16-bit programmable General Purpose Timer that can be used to
generate periodic system interrupts. The resolution of this timer is 100uS.
The GPT loads the
GPT_LOAD field of the
TIMER_EN bit of the
a chip-level reset, or when the TIMER_EN bit changes from asserted (1) to de-asserted (0), the
GPT_LOAD field is initialized to FFFFh. The
also initialized to FFFFh on reset. Software can write a pre-load value into the GPT_LOAD field at any
time (e.g. before or after the TIMER_EN bit is asserted).
Once enabled, the GPT counts down until it reaches 0000h, or until a new pre-load value is written to
the GPT_LOAD field. At 0000h, the counter wraps around to FFFFh, asserts the GPT interrupt status
bit (GPT_INT) in the
set in the
this bit is asserted, it can only be cleared by writing a 1 to the bit. Refer to
Purpose Timer Interrupt," on page 53
The Free-Running Clock (FRC) is a simple 32-bit up-counter that operates from a fixed 25MHz clock.
The current FRC value can be read via the
assertion of a chip-level reset, this counter is cleared to zero. On de-assertion of a reset, the counter
is incremented once for every 25MHz clock cycle. When the maximum count has been reached, the
counter rolls over to zeros. The FRC does not generate interrupts.
Note: The free running counter can take up to 160nS to clear after a reset event.
General Purpose Timer
Free-Running Clock
Interrupt Status Register
Interrupt Status Register
General Purpose Timer Count Register (GPT_CNT)
General Purpose Timer Configuration Register (GPT_CFG)
General Purpose Timer Configuration Register (GPT_CFG)
DATASHEET
(INT_STS)), and continues counting. GPT_INT is a sticky bit. Once
for additional information on the GPT interrupt.
162
Two Port 10/100 Managed Ethernet Switch with 16-Bit Non-PCI CPU Interface
Free Running 25MHz Counter Register
(INT_STS), asserts the IRQ interrupt (if GPT_INT_EN is
General Purpose Timer Count Register (GPT_CNT)
Section 5.2.7, "General
SMSC LAN9311/LAN9311i
with the value in the
is asserted (1). On
(FREE_RUN). On
when the
Datasheet
is