The MitySOM-A10S features two on-SoM boot media options; micro-SD card and an optional eMMC memory.
The eMMC and micro-SD card share the same MMC bus connected to the HPS of the Arria 10 SoC using an onboard multiplexed interface. The default boot device is the microSD card but the eMMC can be selected by the use of a GPIO control pin to support accessing both devices, one at a time, while running. In addition, the default boot media can be changed to use the eMMC device by default by tying the BOOT_MEDIA_SELECT pin on J4 pin 40 to ground.
Boot Media Interface Description¶
The micro-sd card and eMMC (when populated) devices share the same MMC interface connected to the HPS of the Arria 10 SoC through a MUX.
|Arria 10 SoC Ball||Boot Media Function|
Note that these pins cannot be muxed in the Arria 10 SoC HPS for other peripheral modes, i.e. GPIO, NAND or QSPI.
Boot Media Select¶
Users can select between EITHER the eMMC or micro-SD card as described below through the use of either the GPIO SW control pin or external BOOT_MEDIA_SELECT which are wire-or'd together on the module.
Note that there is a 1.8V pull-up resistor, 100K, after the wire-or and a 1.0k series resistor for the external BOOT_MEDIA_SELECT pin on the module.
GPIO control pin¶
Users can control which media is selected by changing the state of a GPIO control pin connected to the Arria 10 SoC at Bank 2A Ball AD19.
- Setting this pin high will select the micro-SD card
- Setting this pin low will select the eMMC
- Floating this pin will select the micro-SD card (unless the external BOOT_MEDIA_SELECT is pulled low, then that will take priority)
Note that you can switch between the devices while running through this GPIO pin, after the system has booted, however you may only access one device at a time.
External "BOOT_MEDIA_SELECT" pin¶
This pin is exposed on the J4B connector at Pin 40 and is meant to change the default boot media from the micro-SD card to the on-SoM eMMC device. To do so this pin should be tied directly to ground (GND).
- Leaving this pin floating (on-SoM pull-up to 1.8V) will cause the module to boot from the default micro-sd card
- Pulling this pin low (GND) will cause the module to boot from the eMMC
This pin should NEVER be driven high. When left floating the on-SoM 100K pull-up to 1.8V will guarantee that either the GPIO SW pin can control the boot device or, when not controlled, that the micro-sd card will be the default boot device.
In the case of our development board we integrated a switch, S200, to allow for the default boot media to be switched as needed.
- The Micro-SD card cage on the module is a push-push type.
- VDD to the Micro-SD card is connected to 3.3V.
- It does NOT have the card detect signal routed from it to the Arria 10 SoC.
- The eMMC, when populated, operates on the same 4-bit wide MMC interface as the micro-SD card through the on-SoM mux.
- Currently MitySOM-A10S modules are either populated with an 8GB (gigabyte) eMMC or no eMMC at all. Other size options may be available, please contact firstname.lastname@example.org for additional information if needed.
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