Side-Mounted Display
The RGB-MIPI bridge has still held me back on the project for the longest time but I feel as I am getting close to a final solution.
FPGA
I have started to have doubts about using GOWIN FPGAs due to the company being listed under the U.S. Department of Commerce Entity List and possible issues with long-term sourcing. To lower risk of continued use, on March 13, 2025, I have decided to switch to using a Lattice FPGA, specifically the CrossLinkPlus MDF6000-6KMG80I that seems to be designed specifically for the purpose of converting from and to MIPI DSI/CSI. This device, however uses a relatively small pitch FBGA package and costs about US$8 more than the GOWIN FPGA I was using before; it has a price of about US$20 per unit.
On March 13, 2025, I drew the footprint as it was not already in KiCAD, being the first BGA package footprint I have drawn. The process of drawing the footprint was not as difficult I expected. The symbol, however, is the tedious part.
On March 14, 2025, I found out about a lower cost FPGA from Lattice that is in the CrossLink-NX series, the LIFCL-17-7SG72C. Though US$16.30, it is in a QFN package that is much easier to work with while costing less than the MDF6000-6KMG80I. I may cut costs later on by using smaller FPGA packages but for now, I will use the LIFCL-17-7SG72C.
As a QFN-72 footprint was already in KiCAD, I did not have to draw it myself. The symbol, however, I had to draw myself but I found a way to significantly reduce the amount of work by using the Pin Table tool to effectively copy and paste the pin assignments from the provided pinout CSV file for the LIF-CL-17 series. All what I was left to do was assign pins to units based on FPGA banks.
Symbol
On March 16, 2025, I drew the symbol for the LIFCL-17-7SG72C. I broke up the symbol into blocks based on their bank number:
- Bank 0: Unit A
- Bank 1: Unit B
- Bank 3: Unit C
- Bank 5: Unit D
- Bank 60: Unit E
- Power Supply + Bank 70: Unit F
There does not seem to be a Bank 2 on the LIFCL-17 while Bank 4, Bank 61 (second MIPI DPHY) and Bank 70 are not present on the LIFCL-17-7SG72C specifically. One thing I noticed is that there are no ground pins on this part while it appears that the EP (Exposed Pad) is used for ground. In the spreadsheet, there is only one pin under Bank 70, named VCCADC18 which I decided to have part of the power supply unit.
Battery
Recently, though more like within the last few months, I have started to consider using four 1S3P 10050mAh Li-Ion battery packs with a custom BMS board. This would provide about 148Wh. This is about 3.72 times the battery capacity of the Steam Deck at 40Wh and 1.7 times the capacity of the HP FM08 battery pack at 86Wh.
This would require yet another custom PCB but the ability to define the pinout and size is important. I did write about this in the documentation in January though I have not yet mentioned it in a blog post until now.
Carrier PCB
I do not expect to start work on the carrier PCB soon. Due to its immense complexity while some of its features are to determined by the layout of other PCBs, I expect to work on it last.
Ethernet
Yet another thing I wrote in the documentation that I did not mention in a blog post is that I decided to not implement the Ethernet port and instead, have Ethernet provided by an M.2 PCIe module. This eliminates the need to implement an Ethernet controller myself and allows for the Ethernet NIC to be replaced or removed.
SMEC
With SMEC, I have had the idea to put the SP7021 on its own system on module that connects to the main carrier board, using the same connectors as the Raspberry Pi Compute Module 4/5. This increases cost and complexity but it also allows for the SP7021 to be replaced or removed (though the system cannot operate without it). I did not come up with this idea myself, someone in the LattePanda Mu Discord mentioned it a while back.
The System on Module could be its own project, possibly being named "Square-SP7021", in relation to the single-board computer being named "Block-SP7021".
I doubt that I would actually put the SP7021 on its own system on module.
Display
The eDP adapter for the display is still a work in progress.
Software
On March 12, 2025, I removed the "mct2-smec-kernel" repository on GitHub. It contained nothing more than a copy of the latest Linux release. Due to the immense size of the Linux kernel, this caused problems with external tools that read my repositories, having 98% of my repositories as C source code despite that I have written none of it.
Instead, I am going to use the kernel repository provided by Tibbo/Sunplus and modify that to my needs.