I have used following command to program my Acer C720:

./flashrom -p internal:ich_spi_forces=yes -V -N --ifd -i bios -w peppy/coreboot-peppy-seabios-latest.ro    m  > ferr.txt 2>&1

The eprom chip in this computer is: 25Q64FVSIG and yes I have remover write protection screw.

I have received following response from this flashrom command:
flashrom v1.0 on Linux 4.9.0-8-amd64 (x86_64)
flashrom is free software, get the source code at https://flashrom.org

flashrom was built with libpci 3.5.2, GCC 6.3.0 20170516, little endian
Command line (9 args): ./flashrom -p internal:ich_spi_forces=yes -V -N --ifd -i bios -w peppy/coreboot-peppy-seabios-latest.rom
Using clock_gettime for delay loops (clk_id: 1, resolution: 1ns).
Initializing internal programmer
Found candidate at: 00000500-00000510
Found coreboot table at 0x00000500.
Found candidate at: 00000000-00000194
Found coreboot table at 0x00000000.
coreboot table found at 0x7becf000.
coreboot header(24) checksum: 72d0 table(404) checksum: f9e3 entries: 10
Vendor ID: GOOGLE, part ID: Peppy
Using Internal DMI decoder.
DMI string chassis-type: "Desktop"
DMI string system-manufacturer: "GOOGLE"
DMI string system-product-name: "Peppy"
DMI string system-version: "1.0"
DMI string baseboard-manufacturer: "GOOGLE"
DMI string baseboard-product-name: "Peppy"
DMI string baseboard-version: "1.0"
Found chipset "Intel Lynx Point LP Mainstream" with PCI ID 8086:9c45.
This chipset is marked as untested. If you are using an up-to-date version
of flashrom *and* were (not) able to successfully update your firmware with it,
then please email a report to flashrom@flashrom.org including a verbose (-V) log.
Thank you!
Enabling flash write... Root Complex Register Block address = 0xfed1c000
Error accessing ICH RCRB, 0x4000 bytes at 0x00000000fed1c000
/dev/mem mmap failed: Operation not permitted
Unhandled programmer parameters (possibly due to another failure): ich_spi_forces=yes
Error: Programmer initialization failed.

Also please find attached output of dmidecoed from this C720 computer:

I will appreciate any suggestion.