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imx28 ABPX ABPH Peripherals, Speed vs. imx6

Question asked by wolfgang gaerber on Apr 8, 2013
Latest reply on Nov 6, 2014 by wolfgang gaerber
Branched to a new discussion

Dear All,


Using imx28 bare.metal, we found out that the typical access penalties for certain peripherals are higher than expected:



(this values are somewhat expected)

ABPX-BUS: write: 2-3 X Cycles -> 85-125ns

                  read:  4-6 X Cycles ->170-250ns

This would equal 50-100 waitstates if clocked with 454MHz.



(this was some surprise)

ABPX-BUS: read, write: 6 X Cycles -> 250ns

Using 32 Byte tx - fifo - this means that filling up the fifo may take around 8us, if you do that in a while loop checking for fifo full - 16us.

Bascially - using the Debug Uart is like having a 4MHz peripheral with corresponding waitstates.

This would equal 114 waitstates if clocked with 454MHz.



(some lecture on H Bus)

ABPH-BUS: read, write: 8H Cycles -> 50ns

Because of multiplexed data/address on H bus + some clocks to overcome the different time domains - the actual access time

is around 50ns - which would correspond to access a 24MHz peripheral.

This would equal 23 waitstates if clocked with 454MHz.


This is the reason why using DMA for X and H bus is highly recommended - but not available for debug uart.

Another option is to separate consecutive writes - but thats no option for reads.


Has somebody experience with imx6 peripherals, busses ?

Is the performance similar as described here ?