How does partial erase work?

[mithro]

Originally posted by @DurandA in enjoy-digital/litex#522 (comment)

@mithro Thanks! Strangely, LiteSPI doesn't define a sector size so I wonder how partial erase is done.

[kowalewskijan]

In MMAP mode we have only preconfigured read commands. To erase a sector, block etc. user must enter the Master mode and write a proper command. Using CSRs this procedure should look like this:
spiflash_mmap_cfg_write(1); // switch to Master mode
spiflash_mmap_master_cs_write(1); // CS on
spiflash_mmap_master_phyconfig_write(0x010108); // xfer_len=8, xfer_width=1, xfer_mask=1
spiflash_mmap_master_rxtx_write(SECTOR_ERASE_CMD); // send erase command
spiflash_mmap_master_cs_write(0); // CS off
spiflash_mmap_cfg_write(0); // switch to MMAP mode

Function names are taken from genereated csr.h when you build Arty example.

edit: this is of course for offset 0x0, so to erase a particular data, there should be an address provided after the instruction byte.