Hi, I am looking into flashing coreboot to my 4th generation Haswell motherboard. Usually, this requires a hardware programmer such as the CH341A to interface with the motherboard's SPI flash chip. Looking up the prices for a CH341A kit online, it costs around 500 INR, which feels a bit excessive for a one-off flashing task. While hunting for cheaper alternatives on Robu.in, I came across the WCH CH552T development board, retailing for only 150 INR. Searching online for documentation or repositories on using the CH552 series as a generic SPI flashing tool yielded close to nothing, as most folks stick to the well-trodden CH341A path. I am planning to save money by trying to build it from scratch, so I’ve decided to see if I can write a custom firmware pipeline to turn this tiny 8051-based microcontroller into a makeshift SPI programmer. I haven’t ordered the board just yet, but before I hit "buy," I want to map out the theoretical architecture to see if this budget approach is viable.
Initially, I looked at the flash constraints and thought about storage scaling. However, a look at the datasheet reveals the core challenge: the CH552T contains just 16 KB of internal Flash memory and a tight 1 KB of internal Data RAM (xdata). A standard 4th-gen Haswell motherboard BIOS image (the coreboot.rom file) is usually 8 MB to 16 MB depending on the chip size. Because the motherboard's ROM is roughly 500 to 1,000 times larger than the entire memory space of the CH552T, storing the binary on the microcontroller is physically impossible. The firmware I write for the CH552T cannot act as storage; it must act purely as an SPI Passthrough Bridge.
To attempt this, the project will need to be broken down into a synchronization loop between a host-side script on my laptop and the bare-metal C runtime I'll need to flash onto the CH552T:
coreboot.rom binary on my PC. It will parse and stream the file down a USB cable in precise 256-byte chunks. Why 256 bytes? Because target motherboard SPI chips (like the Winbond W25Q64) cannot handle arbitrary byte streams; they possess internal hardware buffers that natively write data in 256-byte "pages".xdata RAM array, and immediately pulse those bits out over its hardware SPI pins directly into the physical pins of the motherboard's BIOS chip.1 state. Because SPI flash chips can only be electrically cleared in minimum grids of 4 KB Sectors, my script will track boundaries: every 16 pages (4096 bytes), it will pause, command a Sector Erase (0x20), wait for the chip to finish melting gates, and then resume the 256-byte page write loop.An important factor of this budget approach comes down to electrical logic levels. Modern motherboards use ultra-low-voltage 1.8V flash chips, which would fry if hooked up to a standard 5V/3.3V microcontroller. Fortunately, 4th-gen Haswell systems (like old ThinkPads and Intel 8-series desktop boards) almost universally utilize 3.3V SPI flash chips. Since the CH552T development board natively operates at 3.3V logic, I should theoretically be able to jump lines straight from the microcontroller to a SOIC8 test clip clamped onto the BIOS chip without buying external logic level shifters.
I'll order the hardware on Robu.in and see if reality matches the theory. I'll post updates, schematics, and code benchmarks for Part 2 once the hardware arrives and I can verify if it works.