Texas Instruments TMS320C6722 Bus Bridges, Label Bridge Description Master Clock Target Clock

TMS320C6727, TMS320C6726, TMS320C6722

Floating-Point Digital Signal Processors

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SPRS268E –MAY 2005 –REVISED JANUARY 2007

The five bus masters arbitrate for five different target groups:

T1	On-chip memories through the CPU Slave Port (CSP).
T2	Memories on the external memory interface (EMIF).
T3	Peripheral registers through the peripheral configuration bus.
T4	McASP serializers through the dedicated McASP DMA bus.
T5	dMAX registers.

The crossbar switch supports parallel accesses from different bus masters to different targets. When two or more bus masters contend for the same target beginning at the same cycle, then the highest-priority master is given ownership of the target while the other master(s) are stalled. However, once ownership of the target is given to a bus master, it is allowed to complete its access before ownership is arbitrated again. Following are two examples.

Example 1: Simultaneous accesses without conflict

∙dMAX HiMAX accesses McASP Data Port for transfer of audio data.

∙dMAX LoMAX accesses SPI port for control processing.

∙UHPI accesses internal RAM through the CSP.

∙CPU fills program cache from EMIF.

Example 2: Conflict over a shared resource

∙dMAX HiMAX accesses RTI port for McASP sample rate measurement.

∙dMAX LoMAX accesses SPI port for control processing.

In Example 2, both masters contend for the same target, the peripheral configuration bus. The HiMAX access will be given priority over the LoMAX access.

The master priority is illustrated in Figure 2-4by the numbers 1 through 4 in the bus arbiter symbols. Note that the EMIF arbitration is distributed so that only one bridge crossing is necessary for PMP accesses. The effect is that PMP has 5th priority to the EMIF but lower latency.

A bus bridge is needed between masters and targets which run at different clock rates. The bus bridge contains a small FIFO to allow the bridge to accept an incoming (burst) access at one clock rate and pass it through the bridge to a target running at a different rate. Table 2-6lists the FIFO properties of the four bridges (BR1, BR2, BR3, and BR4) in Figure 2-4.

Table 2-6. Bus Bridges

LABEL	BRIDGE DESCRIPTION	MASTER CLOCK	TARGET CLOCK
BR1	DMP Bridge to peripherals, dMAX, EMIF	SYSCLK1	SYSCLK2
BR2	dMAX, UHPI to ROM/RAM (CSP)	SYSCLK2	SYSCLK1
BR3	PMP to EMIF	SYSCLK1	SYSCLK3
BR4	CPU, UHPI, and dMAX to EMIF	SYSCLK2	SYSCLK3

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