SDFS and eMMC-SD Devices

I got hold of one of these to see if it would improve the speed of SDFS access. I formatted it using SystemDisc with a USB card reader, and added the usual firmware and then !Boot. It seemed quite nippy in comparison to normal. Upon putting it in the SD slot of a Pi 4, the machine booted to a supervisor prompt. From this, I deduce it can read the FAT partition.

Trying to “star cat” (Textile workaround) the contents of the filecore partition from said supervisor prompt, I only get a reference to the Disc drive being empty. Checking all SDFS possibilities (star Drive 0, through to star Drive 7) still nothing. I was hoping it was doing the same as the old Compute Module 3 and seeing eMMC as a hard drive. But no.

On typing star Desktop, there is an SDFS icon (:0) on the icon bar, but it reports the same empty disc error message too.

Does anyone know if there is something in SDFS that is preventing this from being seen, maybe? Reads and works perfectly using a USB card reader, just not the inbuilt SD slot.

I wonder if the eMMC is reporting as a non-removable disc (like a classic hard disc), and SDFS is expecting disc-presence information by assuming all devices are removable?

One thing you could try is unplugging and replugging the device, which might make it reinitialise (it has been removed, see, it’s removable). Although perhaps it won’t help if SDFS is making assumptions.

eMMC on a compute module 4 cannot yet be read by RISC OS. Same issue?

I have one of those Raspikey emmc modules on order, I was hoping it would be a drop in replacement for the SD Card too.

eMMC on the Pinebook was added pretty recently, I’m not sure if something similar needs doing to support this?

Oooh! That does sound promising that eMMC support has been added to the Pinebook.
Hopefully it’ll filter into the Pi ROMS too.

I have a CM4 with and without eMMc. Fitting a PCI express USB board seems to overcome the mouse pointer freezes (making it difficult to click in the right place). With the USB board fitted, the on-board pair of USB 2 ports work correctly again after booting. On RISC OS 5.28 stable it sees the eMMc as a hard disc icon but cannot read it. On 5.29 things have improved – it knows it cannot read it so no icon appears.

In both cases (5.28 and 5.29) the CM4 without eMMc runs OK from the SD card.

There seem to be different “types” of eMMC. Willi Theiss activated eMMC in IGEPv5 and OMAP5UEVM a long time ago. Everything related to the activation of the eMMC in the IGEPv5 and also in the OMAP5 UEVM is in the OMAP5 HAL and there in the s.SDIO file. A new HAL device is simply entered here for each additional SDHC or MMC interface. Everything else is then done by the upper layers (SDIODriver). Not sure if this is possible for other.

The eMMc on the cm4 uses an 8-bit bus for speed.

I have now set up my cm4 and I/O board – this has 1Gbyte of RAM and 32Gbyte of eMMc – so that it can dual boot into either Linux or RISC OS via a switch on the GPIO pins (between pins 29 and 30).

With the switch closed it boots into linux and it can see the 32Gbyte USB drive plus its 80Mbyte FAT partition (although this is not used as it boots from SD card) and can also see the 80Mbyte FAT partition on the SD card (which has the same contents plus the files ‘CMOS’ and ‘RISCOS.IMG’). Both have an amended CMDLINE.TXT and CONFIG.TXT to do the dual boot and to refer to the Linux partition via its UUID.

With the switch open it boots into Supervisor mode in RISC OS 5.28 and shows the eMMc as a hard disc icon (but cannot read it) and shows the FAT partition of the Linux 32Gbyte USB drive. If I run !Boot on another USB drive with HrdDisc4 on it, I have a full working desktop in RISC OS.

Now I am in a position to try out various roms to see whether eMMc under RISC OS is working yet. It is easy to copy a different RISC OS ROM image into place using Linux and if it hangs to go back one step.

See Archive 25:5 for how to set up a dual boot on a Pi4.