SMSC LAN9312 - Manual (Page 160)

High Performance Two Port 10/100 Managed Ethernet Switch with 32-Bit Non-PCI CPU Interface
Datasheet
Revision 1.4 (08-19-08) 160 SMSC LAN9312
DATASHEET
11.4 IEEE 1588 Clock/Events
The IEEE 1588 Clock/Events block is responsible for generating and controlling all IEEE 1588 clock
related events. A 64-bit comparator is included in this block which compares the 64-bit IEEE 1588 clock
wi t h a 6 4 - b it Cl o c k Ta r g e t l oa d e d in t h e
1 5 88 C l oc k Tar ge t H i g h- DW O R D Re g is t e r
( 1 5 8 8 _ C L O C K _ TA R G E T _ H I ) a n d 1 5 8 8 C l o c k Ta r g e t L o w - D W O R D R e g i s t e r
(1588_CLOCK_TARGET_LO) .
When the IEEE 1588 clock equals the Clock Target, a clock event occurs which triggers the following:
„ The maskable interrupt 1588_TIMER_INT is set in the 1588 Interrupt Status and Enable Register
(1588_INT_STS_EN) .
„ The RELOAD_ADD bit in the 1588 Configuration Register (1588_CONFIG) is checked to determine
the new Clock Target behavior:
–RELOAD_ADD = 1:
The new Clock Target is loaded from the 64-bit Reload / Add Registers ( 1588 Clock Target
Reload High-DWORD Register (1588_CLOCK_TARGET_RELOAD_HI) and 1588 Clock Target
Reload/Add Low-DWORD Register (1588_CLOCK_TARGET_RELOAD_LO) ).
–RELOAD_ADD = 0:
The Clock Target is incremented by the 1588 Clock Target Reload/Add Low-DWORD Register
(1588_CLOCK_TARGET_RELOAD_LO) .
Note: Writing the IEEE 1588 clock may cause the interrupt event to occur if the new IEEE 1588 clock
value is set equal to the current Clock Target.
The Clock Target reload function (RELOAD_ADD = 1) allows the host to pre-load the next trigger time.
The add function (RELOAD_ADD = 0), allows for a repeatable event. When the Clock Target overflows,
it will wrap around past 0, as will the 64-bit IEEE 1588 clock. Since the Clock Target and Reload / Add
Registers are 64-bits, they require two 32-bit write cycles, one to each half, before the registers are
affected. The writes may be in any order.
11.5 IEEE 1588 GPIOs
In addition to time stamping PTP packets, the IEEE 1588 clock value can be saved into a set of clock
capture registers based on the GPIO[9:8] inputs. When configured as outputs, GPIO[9:8] can be used
to output a signal based on an IEEE 1588 clock target compare event. Refer to
Section 13.2.1, "GPIO
IEEE 1588 Timestamping," on page 163 for information on using GPIO[9:8] for IEEE 1588 time
stamping functions.
11.6 IEEE 1588 Interrupts
The IEEE 1588 hardware time stamp unit provides multiple interrupt conditions. These include time
stamp indication on the transmitter and receiver side of each port, individual GPIO[9:8] input time
stamp interrupts, and a clock comparison event interrupt. All IEEE 1588 interrupts are located in the
1588 Interrupt Status and Enable Register (1588_INT_STS_EN) and are fully maskable via their
respective enable bits. Refer to Section 14.2.5.23, "1588 Interrupt Status and Enable Register
(1588_INT_STS_EN)," on page 226 for bit-level definitions of all IEEE 1588 interrupts and enables.
All IEEE 1588 interrupts are ANDed with their individual enables and then ORed, as shown in
Figure 11.1 , generating the 1588_EVNT bit of the Interrupt Status Register (INT_STS) .
When configured as an input, GPIO[9:8] have the added functionality of clearing the Clock Target
interrupt bit (1588_TIMER_INT) of the
1588 Interrupt Status and Enable Register (1588_INT_STS_EN)
on an active edge. GPIO inputs must be active for greater than 40 nS to be recognized as clear events.
For more information on IEEE 1588 GPIO interrupts, refer to
Section 13.2.2, "GPIO Interrupts," on
page 163 .
Refer to Chapter 5, "System Interrupts," on page 49 for additional information on the LAN9312
interrupts.