1115
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Multichannel Audio Serial Port (McASP)
Example 24-5. DSP Service Time Calculation for Transmit DMA Event (AXEVT)
The following is an example to show how to calculate DSP Service Time. Assume the following setup:
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Device: CPU at 300 MHz
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McASP transmits in I2S format at 192 kHz frame rate. Assume slot size is 32 bit
With the above setup, we obtain the following parameters corresponding to
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Calculation of McASP system clock cycle:
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CPU uses SYSCLK2 as the McASP system clock. It runs at 150 MHz (half of device frequency)
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Therefore, McASP system clock cycle = 1/150 MHz = 6.7 ns
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Calculation of ACLKX clock cycle:
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This example has two 32-bit slots per frame, for a total of 64 bits per frame
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ACLKX clock cycle is (1/192 kHz)/64 = 81.4 ns
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Time Slot between AXEVT events:
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For I2S format, McASP generates two AXEVT events per 192 kHz frame
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Therefore, Time Slot between AXEVT events is (1/192 kHz)/2 = 2604 ns
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AXEVT Latency
= 5 McASP system clocks
= 6.7 ns × 5 = 33.5 ns
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Setup Time
= 3 McASP system 4 ACLKX cycles
= (6.7 ns × 3) + (81.4 ns × 4)
= 345.7 ns
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DSP Service Time
= Time Slot - AXEVT Latency - Setup Time
= 2604 ns - 33.5 ns - 345.7 ns
= 2225 ns