Doesn’t time fly? It’s been 6 months since my last post! My only excuse is that I started a new job and learning a new culture and processes is pretty exhausting. I have tended to work on this project during the evening, but kids being what they are, rarely co-operate when you need some project time. Time to work on the CPC2 has been limited indeed.
There’s been a fair bit of activity though, so let’s take you though what has been done.
The CPC disk operations are working! The video below shows the CPC loading a disk image from the eMMC, saving new files and unloading the disk image back to the eMMC. The image on the right is the UART console, which is also used to issue the mount and unmount commands (via ‘m’ and ‘u’ commands).
This post talks about HyperRAM, what it is, how to interface to it and how to improve the performance of high-speed parallel interfaces.
HyperRAM is described well by Cypress. It is essentially a double data rate RAM with a compact 12-line interface that masks the underlying technology of a DDR SDRAM. It can provide 333MB/s of data transfer in short bursts. Data is transferred on both edges of the clock, and the narrow bus makes it ideal for microprocessors or pin-constrained FPGAs. Continue reading →
Tented Vias – who’d have thought they play such an essential role? If you have no idea what tented vias are, then you’re not alone and I’m here to enlighten you.
Sadly, this is not a post documenting success, but another important lessons learned. I mentioned in a previous post that I had tired of my custom hardware failing every time I try to solder the next component to the mainboard, so I opted to work on a development board until most of the RTL was proven, and only then move back to custom hardware. I tried the Cyclone V GX Starter kit, but this was lacking a few features like the USB controller I wanted, and was simply too big. I rapidly switched to the fantastic Terasic DE10-Nano SOC. It had a serial interface, the same ADV7513 video chip as my custom board, SDCard and the same USB PHY. All I needed to add was some memory. The DE10-Nano has two expansion ports, so it’s easy to add a daughter board that provides this memory capability:
Another update and another dead end. In an attempt to add the much-needed storage mentioned in my last post, I managed to damage the board so that the JTAG connection stopped working. I added the EPCQ configuration flash chip to the board, only to find that I’d wired the data in and data out back to front and the flash can’t be read from the FPGA. I looked at direct access through the ASMI connection, but I couldn’t get this working. I guess it doesn’t expect the chip to be wired in ‘backwards’! In a futile recovery attempt, I tried to solder in the spare 16G eMMC card, but managed to short out the power pins again. Upon desoldering the eMMC, I must have damaged something because the JTAG connection stopped working. The chip could still be programmed through the supervisor connection on the fast-passive-parallel port, so it was not extensively damaged, but the JTAG connection was pretty essential to efficient RTL development. For now the board is relegated to the ‘post-project-review’ bin. Developing the hardware, RTL and software all in parallel creates too much inefficiency. So I decided to use this board to finish the development, the Terasic Cyclone V GX Starter:
Time for a quick update. I’ve integrated the SDRAM controller, the byte cache, and created some logic to map some of the SDRAM address space to the CPC ROM enable line. I also created some logic to allow the support CPU to push data into the SDRAM. This means that the support CPU can alter the ROM configuration of the CPC2 based on a user-set configuration.
To test the set-up, I created an example ROM that when booted by the CPC, it copies itself to address 0x4000, then dumps 64 bytes of memory at 0x4000. This will test the SDRAM controller, the cache and the cache replacement algorithm. Here’s the output.