iCEBlaster. STM32 based iCE40 SPI bitstream loader tool with USB MSC Drag and Drop feature.
iCEBlaster is a Drag and Drop firmware loader via SPI for iCE40 FPGA. The brain of this project is based on STM32F042F6P6 Arm Cortex M0 microcontroller.
By using USB-FS library working as USB Mass storage device class (USB MSC) and with Virtual file system based on FAT12. Working together as USB Disk pre formatted with FAT12 file system with 512 Bytes per sector, 65535 total sectors, 4 sectors reserved for master boot record (sector 0) and File allocation tables(sector 1, 2 and 3). No longer use internal flash as medium storage. By copying the iCE40 FPGA Bitstream to the disk, 2 for loops in state machine inside STORAGE_Write_FS() receive data from USB buffer and send it over SPI in chucks of 512 bytes to FPGA. With this technique, no Internal flash is required.
The iCE40's Bitstream loading sequence is something like this
// Reset and enter SPI mode sequence.
1. Pull SPI CE Pin to Low
2. Pull CRESET Pin to Low
3. Wait for 2ms.
4. Release CRESET (to HIGH). At this point iCE40 is now in Slave SPI mode.
5. wait for 200ms to make sure iCE40's Configuration RAM (CRAM) is cleared.
// Bitstream loading sequence.
6. Sending Bitstream data via SPI bus (MSB first for each byte).
7. Send 12 dummy bytes (0x00).
8. (optional) Send 7 dummy bytes (0x00) and the SPI pin can be later reconfigure to use as normal PIO
// End of loading.
9. Release SPI CE Pin (to HIGH). The iCE40 will automagically start.
When done, The mcu release CRESET to let FPGA run the firmware that we just flash. Then perform the USB reconnect to have a new and ready to Drag and Drop USB Disk.