SMSC LAN9312 - Manual (Page 57)

High Performance Two Port 10/100 Managed Ethernet Switch with 32-Bit Non-PCI CPU Interface
Datasheet
SMSC LAN9312 57 Revision 1.4 (08-19-08)
DATASHEET
6.2.2 Switch Fabric CSR Reads
To perform a read of an individual switch fabric register, the read cycle must be initiated by performing
a single write to the
Switch Fabric CSR Interface Command Register (SWITCH_CSR_CMD) with
CSR_BUSY (bit 31) set, the CSR_ADDRESS field (bits 15:0) set to the desired register address, the
R_nW (bit 30) set, and the AUTO_INC and AUTO_DEC fields cleared. Valid data is available for
reading when the CSR_BUSY bit is cleared, indicating that the data can be read from the
Switch Fabric
CSR Interface Data Register (SWITCH_CSR_DATA) .
A second read method may be used which utilizes the auto increment/decrement function of the Switch
Fabric CSR Interface Command Register (SWITCH_CSR_CMD) for reading sequential register
addresses. When using this method, the Switch Fabric CSR Interface Command Register
(SWITCH_CSR_CMD) must first be written with the auto increment(AUTO_INC) or auto
decrement(AUTO_DEC) bit set, the CSR_ADDRESS field written with the desired register address,
and the R_nW bit set. The completion of a read cycle is indicated by the clearing of the CSR_BUSY
bit, at which time the data can be read from the
Switch Fabric CSR Interface Data Register
(SWITCH_CSR_DATA) . When the data is read, the address in the Switch Fabric CSR Interface
Command Register (SWITCH_CSR_CMD) is incremented or decremented accordingly, and another
read cycle is started automatically. The user should clear the AUTO_INC and AUTO_DEC bits before
reading the last data to avoid an unintended read cycle.
Figure 6.2 illustrates the process required to perform a switch fabric CSR read. The minimum wait
periods as specified in Table 8.1, “Read After Write Timing Rules,” on page 102 are required where
noted.
Figure 6.1 Switch Fabric CSR Write Access Flow Diagram
Idle
Write Data
Register
Write
Command
Register
Read
Command
Register CSR_BUSY = 0
CSR Write
CSR_BUSY = 1
Idle
Write Data
Register
Write
Command
Register
Read
Command
Register
CSR_BUSY = 0
CSR Write Auto
Increment /
Decrement
CSR_BUSY = 1
Idle
Write
Direct
Data
Register
Range
Read
Command
Register CSR_BUSY = 0
CSR Write Direct
Address
CSR_BUSY = 1
min wait period min wait period
min wait period