Peak Rate Shaping Function; General - NEC mPD98410 User Manual

3.7 Peak Rate Shaping Function

The µ PD98410 has a simple peak rate shaping function for each logical output port. This shaping function takes
effect on the transfer throughput per UTOPIA interface that is determined by SWCLK, and not on the transfer rate of
the UTOPIA interface that is determined by UCLK3 through UCLK0.
The transfer throughput per UTOPIA interface and transfer throughput after shaping can be calculated from the
value set to SPR of the PT register as follows, with 44 SWCLK as one basic cycle:
• Transfer throughput [bps] = SWCLK frequency [Hz] ÷ 44 [SWCLK] × 53 [octet] × 8 [bits]
• Transfer throughput after shaping [bps] = Transfer throughput [bps] ÷ (SPR + 1)
For example, where SWCLK = 33 MHz and SPR = 3, output is suppressed to once in every 4 basic cycles (SPR +
1 = 4), and the transfer throughput after shaping is 79.5M bps.
When two or more logical output ports connected to the same UTOPIA interface simultaneously issue a cell
transmission request, an output conflict occurs. As a result, the transfer throughput of the logical output port that
cannot output data drops.
correction function to shorten the next cell transfer interval of the logical output port that could not output data up to
11 basic cycles by the number of basic cycles (N) kept waiting by the output conflict (SPR + 1 – N).

3.7.1 General

(1) UTOPIA interface and logical output port
The µ PD98410 has four UTOPIA interfaces conforming to UTOPIA Level2. The relationship between the output
enable timing of each UTOPIA interface and the internal basic cycle operation of the µ PD98410 is as shown
below.
Figure 3-42. Relationship between Internal Basic Cycle and Output Enable Timing of Each UTOPIA Interface
Basic operation cycle
UP0 to UP3: UTOPIA interface 0 to 3
CHAPTER 3 FUNCTIONAL OUTLINE
The µ PD98410 prevents this drop in transfer throughput by using a shaping error
UP0
UP1
UP2
UP3
: Timing at which output permission is granted to UP0 to UP3
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