Ezynq

Ezynq project is started to create a bootloader for systems based on the Xilinx Zynq SoC without the inconvenience of the non-free tools and/or files. The goal is not just to "free" the code, but to provide users with the higher degree of flexibi- lity in fine-tuning of the configuration parameters.

Initial release includes configuration for the MicroZed board we used for this software develop- ment, we plan to add support for more boards, including Elphel NC393 camera - the reason we started this project.

Ezynq partially duplicates functionality of Xilinx proprietary tools - bootgen and fsbl (first stage boot loader). It does not support secure boot functionality (that we have no interest in) and loading the FPGA (PL) part with the bitstream - we plan to do that under control of the operating system as we did in our earlier products, if needed this feature can be implemented using U-boot.

This software consists of Python program that processes data from U-boot configuration files (configuration parameters start with CONFIG_EZYNQ_ prefix) that are collected in include/autoconf.mk (it is generated by "make include/autoconf.mk") and generates several output files:

1. the header file (default name boot_head.bin) formatted for the Zynq ROM Boot Loader (RBL) according to section 6.3.2 of Xilinx UG585 -"Zynq-7000 AP SoC Technical Reference Manual". This file uses RBL register initialization feature to set registers (MIO, DDR) that can be written before system clocks and DDR memory are initialized - that requires polling status information and waiting for particular states are reached.

2. ezynq.c file to be compiled and linked with other U-boot files. All ezynq-specific code is called by a modified version of the arch_cpu_init() function - the only difference from the U-boot version for Xilinx Zynq designed to be used with the proprietary FSBL program. This code finishes register initialization (contrary to RBL it can wait for certain states are reached) and performs relocation of the code from the on-chip memory (OCM) to the main system memory, U-boot takes over from there. Optionally the debug code is generated that controls the LED state at different stages of the boot process and outputs register states to the serial port.

3. html output file (default name u-boot.html) that lists the configuration parameters used (specified and calculated from others), used PLLs and clocks, configured interfaces and their usage of the MIO pins. It then lists all the registers written by RBL and written/tested during execution of the arch_cpu_init(). Most of the registers are listed in the same sequence as they are set in hardware, the very last ones show registers that may be set/tested multiple times (as related to UART debug data output). The software keeps track of the register data writes and uses the default values provided in UG585, so when only some bit fields of the whole register need to be modified, software relies on the calculated previous value and does not perform read operations on the actual registers before writing the modified data back.

The U-boot version designed to be used with FSBL relied on it to initialize registers, clocks and DRAM memory, load U-boot image to DRAM at address 0x4000000 and pass control there. FSBL itself was loaded by RBL into on-chip memory (OCM) at address 0, having 192K of the total 256K mapped to 0x0..0x2ffff and the remaining 64K - to the upper 0xffff0000..0xffffffff, the same mapping is passed to U-boot that uses the high OCM memory for stack initially and later remaps all of the OCM to 0xfffc0000.0xffffffff. Starting from 0x4000000 U-boot relocates itself to address zero and runs there.

When using Ezynq the size of the U-boot image is limited to 192K - it is all what Zynq RBL can load by itself. It is quite a lot (192K is just for code, data uses DRAM and is not limited by the OCM) so U-boot can be loaded in a simple one-stage process without the need of the SPL when first a mini-version of U-boot is loaded, and that version later loads the full U-boot to DRAM.

Generated arch_cpu_init() starts running in OCM, initializes DRAM, copies itself (first 192K OCM) to DRAM to 0x4000000.0x402ffff (using just C, not assembly code) and than adds 0x4000000 to the program counter. In this state it is possible to map DRAM to the 0x0.0x2ffff instead of the OCM and copy 0x4000000.0x402ffff back to 0x0.0x2ffff and so return from the function arch_cpu_init() gets the execution to the same low address where it started, but now it is in the DRAM, not in the OCM. U-boot relocation functionality nicely skips actual relocation (as the source and destination addresses are the same) and the data memory is initialized when 192K OCM limit is not in effect anymore.

SUPPORTED BOARDS

• Avnet MicroZed
• Xilinx ZC706
• Elphel 10393
• Digilent/Avnet Zedboard (not yet tested)

INSTALLATION (see below for testing without U-boot installation)

When Ezynq repository is cloned, there is install_uboot.sh script in the top directory. Running this script clones u-boot-xlnx and then adds links to the files in Ezynq sub-directory u-boot-tree from the corresponding directories of the u-boot-xlnx, that allows to update Ezynq project files by "git pull".

These links created by install_uboot.sh add new configuration files and replace 3 files in the u-boot-xlnx:

• boards.cfg - adding zynq-microzed there
• arch/arm/cpu/armv7/zynq/cpu.c - disabling arch_cpu_init() there if configuration was made for Ezynq
• arch/arm/cpu/armv7/zynq/Makefile - to add autogenerated (not in the repository) arch/arm/cpu/armv7/zynq/ezynq.c

New files include (for microzed):

• include/configs/zynq_microzed.h configuration parameters for U-boot features, described in U-boot README file
• include/configs/ezynq/ezynq_MT41K256M16RE125.h - Ezynq configuration parameters containing Micron DDR3 memory datasheet for the memory used by MicroZed board
• include/configs/ezynq/ezynq_XC7Z010_1CLG400.h - Ezynq configuration parameters containing Xilinx Zynq datasheet data for the SoC used by MicroZed board
• include/configs/ezynq/ezynq_microzed.h - rest of the Ezynq configuration parameters (it has the include lines for the 2 datasheet files listed above)
• makeuboot - script that configures U-boot for the microzed board, creates include/autoconf.mk, runs ezynqcfg.py to create Ezynq code (RBL header and ezynq.c), builds and links U-boot generating u-boot.bin, reruns ezynqcfg.py to include the length of the u-boot.bin into boot_head.bin and then combines boot_head.bin and u-boot.bin into boot.bin with a simple 'cat' command.

Testing without u-boot and cross-compiler toolchain

It is possible to try just the ezynqcfg.py script without building u-boot, no ARM toolchain is required
./ezynqcfg.py -c test.mk --html test.html --html-mask 0x3ff --lowlevel ezynq.c This command uses a demo test.mk that mimics include/autoconf.mk and generates test.html and ezynq.c files

Useful links

• Ezynq wiki page
• meta-ezynq - recipes for Yocto Poky

Known issues

1. [FIXED] Linux: USB does not work yet.
2. [FIXED] Linux: Ethernet is not tested (on the board we have it does not work with provided images, so we suspect a hardware problem.
3. Bitstream loading is not tested, current code does not enable level shifters - it may be more appropriate to do just before loading of the bitstream.
4. Write level training for DDR memory doesn't work in MicroZed and ZC706

Trademark notices

Xilinx® and Zynq® are registered trademarks of Xilinx.

Ezynq project is not endorsed by or affiliated with Xilinx Inc.