Signaloid Core Communication Scheme

Communication between the device application that runs on the Signaloid Core, and the host application that runs on the host device, is achieved over the SD interface via block read and write commands. Specifically, the Signaloid Core supports control and status registers, as well as data buffers, for communication with the host device, which are exposed in the Signaloid Core as memory-mapped I/O (MMIO). Following are the memory addresses used by the device application to access them:

MMIO Communication registers

Register	Memory Address	Size	Device Operation
status	0x40000000	4 Bytes	W
SoC Control	0x40000004	4 Bytes	W
command	0x40000008	4 Bytes	R

status register

This register is set by the device application and can be used to declare the current status of the application.

SoC Control register

This register is set by the device application to control SoC peripherals, and can be read by the host via the SD interface.

Register Bit	Usage
31:2	Reserved
1	Set CONFIG_DONE pin
0	Set onboard red LED

command register

This register can be set by the host application, and read by the device application. It is used for sending commands to the Signaloid Core.

The specific values of the command and status registers for communication between the host and the device are application dependent.

MMIO Data buffers

Additionally, the core offers data buffers for extended I/O

Register	Memory Address	Size	Device Operation
MISO_BUFFER_ADDRESS	0x40010000	4 KiB	W
MOSI_BUFFER_ADDRESS	0x40020000	4 KiB	R

MOSI_BUFFER

This is the MOSI (Master Out Slave In) data buffer for sending data from the host application to the device application.

MISO_BUFFER

This is the MISO (Master In Slave Out) data buffer for sending data from the device application to the host application.

Device application example

In a C based device application, storing the value 0x00000002 to the status register can be done in the following way:

#include <stdint.h>

enum {
	kSignaloidCoreDeviceConstantsStatusAddress = 0x40000000
}

main(void)
{
	volatile uint32_t *	mmioStatus = (uint32_t *) kSignaloidCoreDeviceConstantsStatusAddress;
	...

	*mmioStatus = 0x00000002;
}

SD interface addressing

Following are the address offsets for communication with the C0-microSD over the SD interface while in Signaloid Core mode.

Address space	Address Start	Size	Host Operation	Description
STATUS_REGISTER_OFFSET	0x000000	4 Bytes	R	Offset for status register
SOC_CONTROL_REGISTER_OFFSET	0x000004	4 Bytes	R	Offset for SoC control register
COMMAND_REGISTER_OFFSET	0x10000	4 Bytes	W	Offset for command register
MOSI_BUFFER_OFFSET	0x50000	4 KiB	W	Offset for MOSI buffer
MISO_BUFFER_OFFSET	0x60000	4 KiB	R	Offset for MISO buffer

Additionally, the following address offsets allow the host device to verify the current active configuration, as well as switch back to the Bootloader mode:

Address space	Address Start	Size	Host Operation	Description
CONFIGURATION_ID_OFFSET	0x020000	4 Bytes	R	Offset for configuration ID
CONFIGURATION_VERSION_OFFSET	0x020004	4 Bytes	R	Offset for configuration version
CONFIGURATION_STATE_OFFSET	0x020008	4 Bytes	R	Offset for configuration state
BOOTLOADER_SWITCH_CONFIG_OFFSET	0x040000	4 Bytes	W	Offset for switching operation modes

CONFIGURATION_ID_OFFSET

This 4-byte word stores the ID of the active configuration (in this case the Signaloid Core). This is used by the toolkit to identify the active mode of operation of the C0-microSD.

CONFIGURATION_VERSION_OFFSET

This 4-byte word stores the current version of the active configuration (in this case the Signaloid Core).

CONFIGURATION_STATE_OFFSET

This 4-byte word stores the current state of the active configuration (in this case the Signaloid Core). Currently, this is used by the toolkit to verify whether the C0-microSD is in SWITCHING state.

BOOTLOADER_SWITCH_CONFIG_OFFSET

This offset is used for switching between operation modes. To achieve this, you can write the 4-byte word SBLD (ASCII Encoded) to this offset.