EmBIOS Monitor Protocol

This article describes the USB communcation protocol of emBIOS monitor.

Endpoints

The emBIOS Monitor interface contains 4 bulk endpoints, in the following order:

• Command OUT Endpoint
• Command IN Endpoint
• Data OUT Endpoint
• Data IN Endpoint

If not stated otherwise, everything is little endian.

General Structure

Each packet send to the Command OUT Endpoint has a 16 byte header. The first 4 bytes, interpreted as a 32bit little endian word, contain the command ID. The meaning of the other bytes depends on the command. For commands that send data to the device, it will immediately follow that header.

After sending a packet to the Command OUT Endpoint, listen on the Command IN Endpoint for a response. The response also has a 16 byte header, followed by an optional data stage, depending on the command. The first 4 bytes of the header, interpreted as a 32bit word, is the status code, the meaning of the other bytes depends on the command.

Status Codes

Status Code	Description
0	Invalid response, you should bail out when receiving this
1	OK (everything went fine)
2	Command not supported
3	Device is busy, retry later (another asynchronous command is already running)

Commands

0: Invalid

Never issue this command. It will be rejected with status code 2.

1: Get device information

Use this command to figure out various device properties.

Get version information

Command Packet

Offset	Size (bytes)	Description
0	4	Command ID (1)
4	4	Requested information type (0)
8	8	Should be zero

Command Packet

Offset	Size (bytes)	Description Response Packet Offset Size (bytes) Description 0 4 Status Code (1) 4 4 SVN Revision Number 8 1 Major version 9 1 Minor version 10 1 Patch version 11 1 Software Type ID 12 4 Device Type ID Software Types Software Type ID Description 0 invalid 1 emBIOS Debugger Hardware Types Device Type ID Description 0 invalid 0x47324e49 iPod Nano 2G 0x47334e49 iPod Nano 3G 0x47344e49 iPod Nano 4G 0x4c435049 iPod Classic Get packet size information Command Packet Offset Size (bytes) Description 0 4 Command ID (1) 4 4 Requested information type (1) 8 8 Should be zero Response Packet Offset Size (bytes) Description 0 4 Status Code (1) 4 2 Maximum Command OUT Endpoint packet size 6 2 Maximum Command IN Endpoint packet size 8 4 Maximum Data OUT Endpoint packet size 12 4 Maximum Data IN Endpoint packet size Get user memory address range Provides information about the range of memory not used by emBIOS itself. Command Packet Offset Size (bytes) Description 0 4 Command ID (1) 4 4 Requested information type (2) 8 8 Should be zero Response Packet Offset Size (bytes) Description 0 4 Status Code (1) 4 4 Lower bound (inclusive) of the usable memory range 8 4 Upper bound (exclusive) of the usable memory range 12 4 Undefined 2: Reset Reboot the device. Command Packet Offset Size (bytes) Description 0 4 Command ID (2) 4 4 Type: Reboot forcibly (0) / Reboot gracefully (1) 8 8 Should be zero Graceful reboots are asynchronous commands. Forced reboots won't send a response packet before rebooting. Response Packet Offset Size (bytes) Description 0 4 Status Code (1 or 3) 4 12 Undefined The response indicates that the request has been acknowledged, however there might be substantial delay before device actually reboots. 3: Power off Power the device off. Command Packet Offset Size (bytes) Description 0 4 Command ID (3) 4 4 Type: Power off forcibly (0) / Shut down gracefully (1) 8 8 Should be zero Both variants are asynchronous commands. Response Packet Offset Size (bytes) Description 0 4 Status Code (1 or 3) 4 12 Undefined The response indicates that the request has been acknowledged, however there might be substantial delay before device actually powers off. 4: Read memory Use this command to read small amouts of memory through the command pipe. You may not request a transfer that would exceed the maximum Command IN Endpoint packet size (including the header). Command Packet Offset Size (bytes) Description 0 4 Command ID (4) 4 4 Memory address to read from 8 4 Number of bytes to be read 12 4 Should be zero Response Packet Offset Size (bytes) Description 0 4 Status Code (1) 4 12 Undefined 16 variable The data read from memory 5: Write memory Use this command to write small amouts of memory through the command pipe. You may not request a transfer that would exceed the maximum Command OUT Endpoint packet size (including the header). Command Packet Offset Size (bytes) Description 0 4 Command ID (5) 4 4 Memory address to write to 8 4 Number of bytes to write 12 4 Should be zero 16 variable The data to be written Response Packet Offset Size (bytes) Description 0 4 Status Code (1) 4 12 Undefined 6: Read memory using DMA Use this command to read large amouts of memory through the data pipe. You may not request a transfer that would exceed the maximum Data IN Endpoint packet size. Command Packet Offset Size (bytes) Description 0 4 Command ID (6) 4 4 Memory address to read from 8 4 Number of bytes to be read 12 4 Should be zero Response Packet Offset Size (bytes) Description 0 4 Status Code (1) 4 12 Undefined After receiving the response, read the requested data from the Data IN Endpoint. 7: Write memory using DMA Use this command to read large amouts of memory through the data pipe. You may not request a transfer that would exceed the maximum Data OUT Endpoint packet size. Command Packet Offset Size (bytes) Description 0 4 Command ID (7) 4 4 Memory address to write to 8 4 Number of bytes to be written 12 4 Should be zero Response Packet Offset Size (bytes) Description 0 4 Status Code (1) 4 12 Undefined After receiving the response, send the data to be written to the Data OUT Endpoint. 8: Read from I2C device Use this command to read from an I2C slave. You may not request a transfer that would exceed the maximum Command IN Endpoint packet size (including the header) or 255 bytes (excluding the header), whichever is smaller. Command Packet Offset Size (bytes) Description 0 4 Command ID (8) 4 1 I2C bus index 5 1 I2C slave address (in the upper 7 bits) 6 1 Start address on the I2C device 7 1 Number of bytes to be read (0 means 256) 8 8 Should be zero I2C transactions are asynchronous commands. Response Packet Offset Size (bytes) Description 0 4 Status Code (1 or 3) 4 12 Undefined 16 variable The data read from the I2C device (undefined if the status code is not 1) 9: Write to I2C device Use this command to write to an I2C slave. You may not request a transfer that would exceed the maximum Command OUT Endpoint packet size (including the header) or 255 bytes (excluding the header), whichever is smaller. Command Packet Offset Size (bytes) Description 0 4 Command ID (9) 4 1 I2C bus index 5 1 I2C slave address (in the upper 7 bits) 6 1 Start address on the I2C device 7 1 Number of bytes to be written (0 means 256) 8 8 Should be zero 16 variable The data to be written to the I2C device I2C transactions are asynchronous commands. Response Packet Offset Size (bytes) Description 0 4 Status Code (1 or 3) 4 12 Undefined 10: Read from the USB console Use this command to get data written to the USB console. You may not request a transfer that would exceed the maximum Command IN Endpoint packet size (including the header). As long as the console application is running, make sure to issue this request at least once a second. Otherwise the console might start dropping data and inserting an "\n\n[overflowed]\n\n" mark. If you can't receive any data but need to keep the console from dropping data, issue zero-length read requests. Command Packet Offset Size (bytes) Description 0 4 Command ID (10) 4 4 Number of bytes requested 8 8 Should be zero Response Packet Offset Size (bytes) Description 0 4 Status Code (1) 4 4 Actual number of valid response bytes 8 4 Size of the on-device USB console read buffer 12 4 Number of bytes still waiting in the on-device USB console read buffer 16 variable Valid console data padded with undefined data to meet the requested size 11: Write to the USB console Use this command to write data to the USB console. You may not request a transfer that would exceed the maximum Command OUT Endpoint packet size (including the header). Command Packet Offset Size (bytes) Description 0 4 Command ID (11) 4 4 Number of bytes to be written 8 8 Should be zero 16 variable Data to be written Response Packet Offset Size (bytes) Description 0 4 Status Code (1) 4 4 Actual number of bytes written (the remainder will have to be resent) 8 4 Size of the on-device USB console write buffer 12 4 Number of bytes still free in the on-device USB console write buffer 12: Write to device's consoles Use this command to write data to one or more of the consoles. This is equivalent to the cwrite system call. You may not request a transfer that would exceed the maximum Command OUT Endpoint packet size (including the header). Command Packet Offset Size (bytes) Description 0 4 Command ID (12) 4 4 Bitmask of consoles to be written to 8 4 Number of bytes to be written 12 4 Should be zero 16 variable Data to be written Response Packet Offset Size (bytes) Description 0 4 Status Code (1) 4 12 Undefined 13: Read from device's consoles Use this command to read data from one or more of the consoles. This is equivalent to the cread system call. You may not request a transfer that would exceed the maximum Command IN Endpoint packet size (including the header). This command will not block until there is data available. Command Packet Offset Size (bytes) Description 0 4 Command ID (13) 4 4 Bitmask of consoles to be read from 8 4 Number of bytes to be read 12 4 Should be zero Response Packet Offset Size (bytes) Description 0 4 Status Code (1) 4 4 Number of bytes actually read 8 8 Undefined 16 variable The data read, padded with undefined data to meet the requested size 14: Flush device's console buffers Use this command to flush one or more console's buffers. This is equivalent to the cflush system call. Command Packet Offset Size (bytes) Description 0 4 Command ID (14) 4 4 Bitmask of consoles to be flushed 8 8 Should be zero Response Packet Offset Size (bytes) Description 0 4 Status Code (1) 4 12 Undefined 15: Get process information Use this command to obtain the current state of the scheduler. You may not request a transfer that would exceed the maximum Command IN Endpoint packet size (including the header). Command Packet Offset Size (bytes) Description 0 4 Command ID (15) 4 4 Offset of first byte requested 8 4 Number of bytes requested 12 4 Should be zero Response Packet Offset Size (bytes) Description 0 4 Status Code (1) 4 4 Process information struct version (incremented each time the format changes) 8 4 Total size of the process information table 12 4 Undefined 16 variable The requested data, padded with undefined data to meet the requested size, if it exceeds bounds 16: (Un)Freeze scheduler Use this command to prevent execution of userspace code on the device while dumping or manipulating critical data. Command Packet Offset Size (bytes) Description 0 4 Command ID (16) 4 4 Lock (1) or unlock (0) the scheduler 8 8 Should be zero Response Packet Offset Size (bytes) Description 0 4 Status Code (1) 4 4 Previous state: Locked (1) or unlocked (0) 8 8 Undefined 17: (Un)Suspend thread Suspend or resume a thread Command Packet Offset Size (bytes) Description 0 4 Command ID (17) 4 4 Suspend (1) or resume (0) the thread 8 4 Thread ID 12 4 Should be zero Response Packet Offset Size (bytes) Description 0 4 Status Code (1) 4 4 Previous state: Suspended (1) or running (0) 8 8 Undefined 18: Kill thread Kill a thread Command Packet Offset Size (bytes) Description 0 4 Command ID (18) 4 4 Thread ID 8 8 Should be zero Response Packet Offset Size (bytes) Description 0 4 Status Code (1) 4 12 Undefined 19: Create thread Create a new thread. This command uses an extended command size of 32 bytes. Command Packet Offset Size (bytes) Description 0 4 Command ID (19) 4 4 Pointer to thread name or NULL 8 4 Pointer to entry point of the new thread 12 4 Pointer to stack of the new thread 16 4 Size of the new thread's stack in bytes 20 4 Type: User thread (0) or system thread (1) 24 4 Priority of the new thread (1-255) 28 4 Initial state: Ready (1) or suspended (0) Response Packet Offset Size (bytes) Description 0 4 Status Code (1) 4 4 ID of the created thread (positive) or error code (negative) 8 8 Undefined 20: Flush CPU caches Flushes the CPU's instruction and data caches Command Packet Offset Size (bytes) Description 0 4 Command ID (20) 4 12 Should be zero Response Packet Offset Size (bytes) Description 0 4 Status Code (1) 4 12 Undefined 21: Execute image Executes an emBIOS executable image. This is an asynchronous command. Command Packet Offset Size (bytes) Description 0 4 Command ID (21) 4 4 Memory address where the image to be executed is located 8 8 Should be zero Response Packet Offset Size (bytes) Description 0 4 Status Code (1, does not mean it actually succeeded) 4 4 The return code of execimage(). Use this to check for success. 8 8 Undefined 22: Read raw boot flash Reads raw data from the boot flash to RAM. This is an asynchronous command. Command Packet Offset Size (bytes) Description 0 4 Command ID (22) 4 4 Memory address to copy the data to 8 4 Bootflash address to read from 12 4 Number of bytes to be copied Response Packet Offset Size (bytes) Description 0 4 Status Code (1) 4 12 Undefined 23: Write raw boot flash Writes raw data to the boot flash. Don't call this unless you really know what you're doing. This is an asynchronous command. Command Packet Offset Size (bytes) Description 0 4 Command ID (23) 4 4 Memory address to read from 8 4 Bootflash address to write to 12 4 Number of bytes to be copied (must be an integer multiple of the boot flash width) Response Packet Offset Size (bytes) Description 0 4 Status Code (1) 4 12 Undefined 24: Execute firmware Executes a firmware image at the specified address. This is an asynchronous command. Command Packet Offset Size (bytes) Description 0 4 Command ID (24) 4 4 Memory address where the firmware image to be booted is located 8 8 Should be zero Response Packet Offset Size (bytes) Description 0 4 Status Code (1) 4 12 Undefined 25: Hardware key AES Encrypt or decrypt a buffer using a hardware key. This is an asynchronous command. Command Packet Offset Size (bytes) Description 0 4 Command ID (25) 4 1 Decrypt (0) / Encrypt (1) 5 1 Should be zero 6 2 Hardware key index 8 4 Memory address of the buffer to be encrypted/decrypted 12 4 Size of the buffer to be encrypted/decrypted Response Packet Offset Size (bytes) Description 0 4 Status Code (1) 4 12 Undefined 26: HMAC-SHA1 Generate a HMAC-SHA1 hash of a buffer. This is an asynchronous command. Command Packet Offset Size (bytes) Description 0 4 Command ID (26) 4 4 Memory address of the buffer to be hashed 8 4 Size of the buffer to be hashed 12 4 Destination address where the hash is stored Response Packet Offset Size (bytes) Description 0 4 Status Code (1) 4 12 Undefined