ARM ARM DUI 0224I manual Operating the AHB bridges in asynchronous mode

Models: ARM DUI 0224I

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Hardware Description

If CPUCLK is 210MHz the total multiplier ratio of HCLKDIV and HCLKEXTDIV must be 6.

The HCLK divider is set to divide by 3 (CFGHCLKDIVSEL[1:0]=b10 ). This gives an internal AMBA bus and SDRAM clock of 70MHz. See Configuration control on page 3-7 and Memory characteristics on page 4-15.

The HCLKEXT divider must be set to divide by 2

(CFGHCLKEXTDIVSEL[2:0]=b001) so that the total divider ratio for HCLKDIV and HCLKEXTDIV is 6. This results in an PLL feedback clock and external HCLK of 35MHz.

CPUCLK is 3*2*35MHz (210MHz) as required.

An MBX clock 70MHz is within the permitted range, so its divider is set to 1 (CFGMBXCLKDIVSEL[1:0]= b00).

An SMC of 70MHz is outside the operating frequency range for flash memory, so the SMC clock divider must be set to 2 (CFGSMCCLKDIVSEL[1:0]= b01). The flash memory in synchronous mode operates at 35MHz.

Operating the AHB bridges in asynchronous mode

The following signals control the external part of the AHB bridges if they are operating in asynchronous mode:

CFGM1ASYNC If HIGH, the external HCLKM1 is selected as the clock for the external part of bus bridge M1. The signal is controlled by the value of bit 22 of the SYS_CONFIGDATA2 register. The default is LOW, the internal clock HCLKEXT is used and the bridge operates in synchronous mode.

CFGM2ASYNC If HIGH, the external HCLKM2 is selected as the clock for the external part of bus bridge M2. The signal is controlled by the value of bit 23 of the SYS_CONFIGDATA2 register. The default is LOW, the internal clock HCLKEXT is used and the bridge operates in synchronous mode.

CFGSASYNC If HIGH, the external HCLKS is selected as the clock for the external part of bus bridge S. The signal is controlled by the value of bit 24 of the SYS_CONFIGDATA2 register. The default is LOW, the internal clock HCLKEXT is used and the bridge operates in synchronous mode.

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ARM DUI 0224I

Page 106
Image 106
ARM ARM DUI 0224I manual Operating the AHB bridges in asynchronous mode