参数资料
型号: IP-POSPHY4
厂商: Altera
文件页数: 38/144页
文件大小: 0K
描述: IP POS-PHY L4
标准包装: 1
系列: *
类型: MegaCore
功能: POS-PHY 4 级接口,链路层/物理层
许可证: 初始许可证
3–16
1
Chapter 3: Parameter Settings
Protocol Parameters
Although the MegaWizard interface allows you to set FTH values as low as one FIFO
buffer element (translated to bytes), a minimum FTH value is used internally. And,
depending on the core's configuration, up to four FIFO buffer locations are unusable.
For the exact minimum FTH value and number of unusable locations, refer to the
MegaWizard interface message that appears while configuring the core.
Receiver Options
The Almost empty (AE) and Almost full (AF) thresholds segregate the receiver FIFO
buffer into three states, depending on the fill levels: starving, hungry, and satisfied.
The SPI-4 Phase 2 specification defines two-bit status values for starving, hungry, and
satisfied. These two-bit values are based on the available space in the FIFO buffer and
on the AE and AF parameter settings:
Starving —when the number of elements in the FIFO buffer is less than, or equal to,
the AE threshold
Hungry —when the number of elements in the FIFO buffer is between the AE
threshold and the AF threshold
Satisfied —when the number of elements in the FIFO buffer is greater than the AF
threshold
The starving, hungry, and satisfied conditions are reported to the adjacent transmitter
on the rstat bus, which operates at up to ? of the rdclk frequency.
These thresholds are defined in terms of bytes, with a valid range from zero to buffer
size .
1
AE must be lower than or equal to AF.
Figure 3–5 illustrates the relationship between the AE and AF thresholds and the
MaxBurst1 and MaxBurst2 values.
Figure 3–5. FIFO Buffer Thresholds
(Empty)
Starving
AE
Hungry
AF
Satisfied
(Full)
Lmax + ε
Lmax + MaxBurst2+ ε
Lmax + MaxBurst1+ ε
Notes to Figure 3–5 :
(1) L MAX corresponds to the worst-case response time from sending a status update over the FIFO status channel until
observing the reaction to that update on the corresponding data path.
(2)
? corresponds to the difference between the granted credit and the actual data transfer length. This difference arises
from various protocol overheads.
(3) The MaxBurst1 and MaxBurst2 values are defined by the adjacent device’s transmitter. Determining the optimal
MaxBurst1 and MaxBurst2 values is application-specific, and requires an analysis of the data flows, beyond the
scope of this user guide.
POS-PHY Level 4 MegaCore Function User Guide
May 2013 Altera Corporation
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