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Purpose

On DRA7xx, Boot ROM copies the first stage boot loader(MLO/SPL) from QSPI at a conservative speed of 11 MBps. A 120 KB binary takes around 11 ms to be copied from QSPI into OCMC. Usually this is not an issue. However there are usecases(e.g. CAN response) where we need to have a specific functionality available in less than 100 ms. In such usecases, the time spent in ROM copy forms a significant portion (10%) of the usecase time. The micro bootloader(umlo) built in this project speeds up this copy.

umlo first sets up the QSPI interface to the maximum speed possible on DRA7xx i.e. 76.8 MHz interface clock, Quad Mode and Mode 0 operation. Then umlo copies the MLO to the execution address in OCMC and jumps to it.

With this change, we see the time taken to enter a 120 KB MLO reduce from 24.5 ms to 19 ms, a saving of 5.5 ms.

Please refer to manifest.html for license information.

Build Instructions

This tool is compiled and tested with gcc-arm-none-eabi-4_9-2015q3. However any baremetal compiler supporting Cortex A15 should work. Please make sure that you have the toolchain installed and have arm-none-eabi-gcc in the path.

Run make to produce the required binaries.

If you are modifiying the toolchain, please ensure that the CROSS_COMPILE option is set correctly in the Makefile.

Flashing instructions

  1. Flash the output file umlo to offset 0x0 in QSPI.

  2. Flash the actual MLO from your normal build process to offset 0x10000 (64 KB).

Nothing else needs to change.

Reboot the EVM in QSPI4 boot mode. umlo boots and reads the actual MLO from offset 0x10000 into OCMC and jumps to it. You will not see any difference in execution except a slight speed up in reading MLO.

For information on measuring time to enter MLO, please see [1] in references.

Undoing the changes

If you suspect a problem is being introduced due to umlo, you can remove it by erasing the first 64 KB of QSPI. This will cause Boot ROM to jump to your MLO.

Development Notes

  1. We used the peripheral boot feature of the DRA7xx Boot ROM heavily for testing umlo during development. If you are customizing umlo, please see [2] and [3] in references on how to use perhipheral boot for debugging.

  2. The Makefile has two sets of build options, one for development and another for release. Please switch to the development build options when debugging.

  3. The file main.c contains an infinite loop function wait_for_debugger(). You can call this function at the point where you want to halt execution in code and single step via CCS from that point.

Caveats

  1. umlo expects that the first 512 bytes of the acutal MLO is the CH Header and skips it. This is the case when MLO is produced from building U-Boot. Please modify the code in main.c if this assumption is not true for the MLO from your build.

  2. umlo does not do any SPI flash specific configuration. umlo expects that the SPI flash has quad read mode enabled. It has only been tested on TI EVM's which have a Spansion flash device.

  3. umlo is loaded to address 0x40330000 to avoid any overlap with the actual MLO. Please modify this address in the Makefile if the actual MLO runtime locations overlap with 0x40330000.

     CONFIG_UMLO_BASE=0x40300000

Support

For support, please post any questions to

https://e2e.ti.com/support/arm/automotive_processors/f/1020

References

  1. Linux Boot Time Optimizations on DRA7xx devices

    http://www.ti.com/lit/pdf/sprac82

  2. Using Peripheral Boot and DFU for Rapid Development on Jacinto 6 Devices

    http://www.ti.com/lit/pdf/sprac65

  3. DRA7xx Bootswitch - Utility for Peripheral boot

    https://git.ti.com/glsdk/dra7xx-bootswitch

  4. Please see the chapter "Initialization" in the Device TRM.