Cypress Semiconductor FX2LP Información técnica descargar pdf (Pagina 206)

EZ-USB FX2 Technical Reference Manual

Page 10-16 EZ-USB FX2 Technical Reference Manual v2.1

Since all States in this example are coded as NDPs, the GPIF automatically branches from the

last State (S6) to the Idle State (S7). This is the State in which the GPIF waits until the next GPIF

waveform is triggered by the firmware.

States 2 and 3 in the example are identical, as are States 5 and 6. In a real application, these

would probably be combined (there’s no need to duplicate a State in order to “stretch” it, since

each NDP State can be assigned a duration in terms of IFCLK cycles). If fewer than 7 States were

defined for this waveform, the Idle State wouldn’t automatically be entered after the last pro-

grammed State; that last programmed State’s State Instruction would have to include an explicit

branch to the Idle State.

10.3.2.2.2 Decision Point (DP) States

Any State can be designated as a Decision Point (DP). A DP allows the GPIF engine to sample

two signals — each of the “two” can be the same signal, if desired — perform a boolean operation

on the sampled values, then branch to other States (or loop back on itself, remaining in the current

State) based on the result.

If a State Instruction includes a control task (advance the FIFO pointer, increment the GPIFADR

address, etc.), that task is always executed once upon entering the State, regardless of whether

the State is a DP or NDP. If the State is a DP that loops back on itself, however, it can be pro-

grammed to re-execute the control task on every loop.

With a Decision Point, the GPIF can perform simple tasks (wait until a RDY line is low before con-

tinuing to the next State, for instance). Decision point States can also perform more-complex tasks

by branching to one State if the operation on the sampled signals results in a logic 1, or to a differ-

ent State if it results in a logic 0.

In each State Instruction, the two signals to sample can be selected from any of the following:

• the six external RDY signals (RDY0-RDY5)

• one of the current FIFO’s flags (PF, EF, FF)

• the INTRDY bit in the READY register

• a “Transaction Count Expired” signal (which replaces RDY5)

The State Instruction also specifies a logic function (AND, OR, or XOR) to be applied to the two

selected signals. If it’s desired to act on the state of only one signal, the usual procedure is to

select the same signal twice and specify the logic function as AND.

The State Instruction also specifies which State to branch to if the result of the logical expression

is 0, and which State to branch to if the result of the logical expression is 1.

Below is an example waveform created using one Decision Point State (State 1); Non-Decision

Point States are used for the rest of the waveform.

1 2 ... 201 202 203 204 205 206 207 208 209 210 211 ... 459 460

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Cypress Semiconductor FX2LP Información técnica Pagina 206