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Manual

VCMAILBOX(7)

Miscellaneous Information Manual

VCMAILBOX(7)

NAME

vcmailbox - the VideoCore mailbox property interface

DESCRIPTION

The mailbox can be used by the ARM on the Raspberry Pi to communicate with the VideoCore processor. From the command line, the vcmailbox(1) can be used for this purpose. The mailbox operates a simple request / response protocol:

•: The response overwrites the request.

•: The callee is not allowed to return a different buffer address, this allows the caller to make independent asynchronous requests.

The buffer itself is 16-byte aligned as only the upper 28 bits of the address can be passed via the mailbox.
All u64/u32/u16 values are in host CPU endian order.
Unknown tags are ignored (the response bit will not be set).
Response may include unsolicited tags.
Response tag lengths may be longer than expected if additional information is provided in a future format.

The response is truncated to the provided buffer length.
Incompatible changes require a new tag so that where the buffer is the size required by a previous version the truncated part should be readable as per the previous version.
Response length indicates the desired length even when it is longer than the buffer size filled.
Tag value length can be used to infer the version of the request/response.

•: Tags should be processed in order except where an interface requires multiple tags for a single operation (like the frame buffer).

Mailbox messages

•: The mailbox interface has 28 bits (MSB) available for the value and 4 bits (LSB) for the channel.

Request message: 28 bits (MSB) buffer address
Response message: 28 bits (MSB) buffer address

•: Channels 8 and 9 are used.

Channel 8: Request from ARM for response by VC
Channel 9: Request from VC for response by ARM (none currently defined)

Buffer contents

u32: buffer size in bytes (including the header values, the end tag and padding)
u32: buffer request/response code

Request codes:

0x00000000: process request
: All other values reserved

Response codes:

0x80000000: request successful
0x80000001: error parsing request buffer (partial response)
: All other values reserved

u8...: sequence of concatenated tags
u32: 0x0 (end tag)
u8...: padding

Tag format

u32: tag identifier
u32: value buffer size in bytes
u32: Request codes:

b31 clear: request
b30-b0: reserved

: Response codes:

b31 set: response
b30-b0: value length in bytes

u8...: value buffer
u8...: padding to align the tag to 32 bits.

VIDEOCORE TAGS

Get firmware revision

Tag:: 0x00000001
Request:: 0 bytes
Response:: 4 bytes

u32: firmware revision

HARDWARE TAGS

Get board model

Tag:: 0x00010001
Request:: 0 bytes
Response:: 4 bytes

u32: board model

Get board revision

Tag:: 0x00010002
Request:: 0 bytes
Response:: 4 bytes

u32: board revision

Get board MAC address

Tag:: 0x00010003
Request:: 0 bytes
Response:: 6 bytes

u8...: MAC address in network byte order

Get board serial

Tag:: 0x00010004
Request:: 0 bytes
Response:: 8 bytes

u64: board serial

Get ARM memory

Tag:: 0x00010005
Request:: 0 bytes
Response:: 8 bytes

u32: base address in bytes
u32: size in bytes

Future formats may specify multiple base+size combinations.

Get VC memory

Tag:: 0x00010006
Request:: 0 bytes
Response:: 8 bytes

u32: base address in bytes
u32: size in bytes

Future formats may specify multiple base+size combinations.

Get clocks

Tag:: 0x00010007
Request:: 0 bytes
Response:: variable bytes (multiple of 8)

u32: parent clock id (0 for a root clock)
u32: clock id
(repeated)

Returns all clocks that exist in top-down, breadth-first order. Clocks that depend on another clock should be defined as children of that clock. Clocks that depend on no other clocks should have no parent. Clock IDs are as in the CLOCK TAGS section below.

CONFIG TAGS

Get command line

Tag:: 0x00050001
Request:: 0 bytes
Response:: variable bytes

u8...: ASCII command line string

Caller should not assume the string is null terminated.

SHARED RESOURCE MANAGEMENT TAGS

Get DMA channels

Tag:: 0x00060001
Request:: 0 bytes
Response:: 4 bytes

u32: mask

Bits 0-15: DMA channels 0-15 (0=do not use, 1=usable)
Bits 16-31: reserved for future use

Caller assumes that the VC has enabled all the usable DMA channels.

POWER TAGS

Unique device IDs

0x00000000: SD Card
0x00000001: UART0
0x00000002: UART1
0x00000003: USB HCD
0x00000004: I2C0
0x00000005: I2C1
0x00000006: I2C2
0x00000007: SPI
0x00000008: CCP2TX
0x00000009: Unknown (RPi4)
0x0000000a: Unknown (RPi4)

Get power state

Tag:: 0x00020001
Request:: 4 bytes

u32: device id

Response:: 8 bytes

u32: device id
u32: state

Bit 0: 0=off, 1=on
Bit 1: 0=device exists, 1=device does not exist
Bits 2-31: reserved for future use

Response indicates current state.

Get timing

Tag:: 0x00020002
Request:: 4 bytes

u32: device id

Response:: 8 bytes

u32: device id
u32: enable wait time in microseconds

Response indicates wait time required after turning a device on before power is stable. Returns 0 wait time if the device does not exist.

Set power state

Tag:: 0x00028001
Request:: 8 bytes

u32: device id
u32: state

Bit 0: 0=off, 1=on
Bit 1: 0=do not wait, 1=wait
Bits 2-31: reserved for future use (set to 0)

Response:: 8 bytes

u32: device id
u32: state

Bit 0: 0=off, 1=on
Bit 1: 0=device exists, 1=device does not exist
Bits 2-31: reserved for future use

Response indicates new state, with/without waiting for the power to become stable.

CLOCK TAGS

Unique clock IDs

0x00000000: reserved
0x00000001: EMMC
0x00000002: UART
0x00000003: ARM
0x00000004: CORE
0x00000005: V3D
0x00000006: H264
0x00000007: ISP
0x00000008: SDRAM
0x00000009: PIXEL
0x0000000a: PWM
0x0000000b: HEVC
0x0000000c: EMMC2
0x0000000d: M2MC
0x0000000e: PIXEL_BVB

All clocks are the base clocks for those peripherals, e.g. 3MHz for UART, 50/100MHz for EMMC, not the dividers applied using the peripheral.

Get clock state

Tag:: 0x00030001
Request:: 4 bytes

u32: clock id

Response:: 8 bytes

u32: clock id
u32: state

Bit 0: 0=off, 1=on
Bit 1: 0=clock exists, 1=clock does not exist
Bits 2-31: reserved for future use

Set clock state

Tag:: 0x00038001
Request:: 8 bytes

u32: clock id
u32: state

Bit 0: 0=off, 1=on
Bit 1: 0=clock exists, 1=clock does not exist
Bits 2-31: reserved for future use (set to 0)

Response:: 8 bytes

u32: clock id
u32: state

Bit 0: 0=off, 1=on
Bit 1: 0=clock exists, 1=clock does not exist
Bits 2-31: reserved for future use

Get clock rate

Tag:: 0x00030002
Request:: 4 bytes

u32: clock id

Response:: 8 bytes

u32: clock id
u32: rate (in Hz)

Next enable rate should be returned even if the clock is not running. A rate of 0 is returned if the clock does not exist.

Set clock rate

Tag:: 0x00038002
Request:: 12 bytes

u32: clock id
u32: rate (in Hz)
u32: skip setting turbo

Response:: 8 bytes

u32: clock id
u32: rate (in Hz)

Next supported enable rate should be returned even if the clock is not running. A rate of 0 is returned if the clock does not exist. The clock rate may be clamped to the supported range.

By default when setting arm freq above default, other turbo settings will be enabled (e.g. voltage, sdram and gpu frequencies). You can disable this effect by setting "skip setting turbo" to 1.

Get max clock rate

Tag:: 0x00030004
Request:: 4 bytes

u32: clock id

Response:: 8 bytes

u32: clock id
u32: rate (in Hz)

Return the maximum supported clock rate for the given clock. Clocks should not be set higher than this.

Get min clock rate

Tag:: 0x00030007
Request:: 4 bytes

u32: clock id

Response:: 8 bytes

u32: clock id
u32: rate (in Hz)

Return the minimum supported clock rate for the given clock. This may be used when idle.

Get turbo

Tag:: 0x00030009
Request:: 4 bytes

u32: id

Response:: 8 bytes

u32: id
u32: level

Get the turbo state for index id. id should be 0. level will be zero for non-turbo and one for turbo.

Set turbo

Tag:: 0x00038009
Request:: 8 bytes

u32: id
u32: level

Response:: 8 bytes

u32: id
u32: level

Set the turbo state for index id. id should be zero. level will be zero for non-turbo and one for turbo. This will cause GPU clocks to be set to maximum when enabled and minimum when disabled.

VOLTAGE TAGS

Unique voltage IDs

0x00000000: reserved
0x00000001: Core
0x00000002: SDRAM_C
0x00000003: SDRAM_P
0x00000004: SDRAM_I

Get voltage

Tag:: 0x00030003
Request:: 4 bytes

u32: voltage id

Response:: 8 bytes

u32: voltage id
u32: value (offset from 1.2V in units of 0.025V)

The voltage value may be clamped to the supported range. A value of 0x80000000 means the id was not valid.

Set voltage

Tag:: 0x00038003
Request:: 8 bytes

u32: voltage id
u32: value (offset from 1.2V in units of 0.025V)

Response:: 8 bytes

u32: voltage id
u32: value (offset from 1.2V in units of 0.025V)

The voltage value may be clamped to the supported range. A value of 0x80000000 means the id was not valid.

Get max voltage

Tag:: 0x00030005
Request:: 4 bytes

u32: voltage id

Response:: 8 bytes

u32: voltage id
u32: value (offset from 1.2V in units of 0.025V)

Return the maximum supported voltage rate for the given id. Voltages should not be set higher than this.

Get min voltage

Tag:: 0x00030008
Request:: 4 bytes

u32: voltage id

Response:: 8 bytes

u32: voltage id
u32: value (offset from 1.2V in units of 0.025V)

Return the minimum supported voltage rate for the given id. This may be used when idle.

Get temperature

Tag:: 0x00030006
Request:: 4 bytes

u32: temperature id

Response:: 8 bytes

u32: temperature id
u32: value

Return the temperature of the SoC in thousandths of a degree C. id should be zero.

Get max temperature

Tag:: 0x0003000a
Request:: 4 bytes

u32: temperature id

Response:: 8 bytes

u32: temperature id
u32: value

Return the maximum safe temperature of the SoC in thousandths of a degree C. id should be zero. Overclock may be disabled above this temperature.

Allocate memory

Tag:: 0x0003000c
Request:: 12 bytes

u32: size
u32: alignment
u32: flags

Response:: 4 bytes

u32: handle

Allocates contiguous memory on the GPU. size and alignment are in bytes. flags contain:

Name	Value	Comments
_	_	_
MEM_FLAG_NORMAL	0	normal allocating alias; don't use from ARM
MEM_FLAG_DISCARDABLE	1 << 0	can be resized to 0 at any time; use for cached data
MEM_FLAG_DIRECT	1 << 2	0xC alias uncached
MEM_FLAG_COHERENT	1 << 3	0x8 alias; non-allocating in L2 but coherent
MEM_FLAG_L1_NONALLOCATING	3 << 2	Allocating in L2
MEM_FLAG_ZERO	1 << 4	Initialise buffer to all zeros
MEM_FLAG_NO_INIT	1 << 5	Don't initialise; default is initialise to all ones
MEM_FLAG_HINT_PERMALOCK	1 << 6	Likely to be locked for long periods of time

Lock memory

Tag:: 0x0003000d
Request:: 4 bytes

u32: handle

Response:: 4 bytes

u32: bus address

Lock buffer in place, and return a bus address. Must be done before memory can be accessed

Unlock memory

Tag:: 0x0003000e
Request:: 4 bytes

u32: handle

Response:: 4 bytes

u32: status

Unlock buffer. It retains contents, but may move. Needs to be locked before next use. status=0 is success.

Release Memory

Tag:: 0x0003000f
Request:: 4 bytes

u32: handle

Response:: 4 bytes

u32: status

Free the memory buffer. status=0 is success.

Execute Code

Tag:: 0x00030010
Request:: 28 bytes

u32: function pointer
u32: r0
u32: r1
u32: r2
u32: r3
u32: r4
u32: r5

Response:: 4 bytes

u32: r0

Calls the function at given (bus) address and with arguments given. E.g. r0 = fn(r0, r1, r2, r3, r4, r5); It blocks until call completes. The (GPU) instruction cache is implicitly flushed. Setting the lsb of function pointer address will suppress the instruction cache flush if you know the buffer hasn't changed since last execution.

Get Dispmanx Resource mem handle

Tag:: 0x00030014
Request:: 4 bytes

u32: dispmanx resource handle

Response:: 8 bytes

u32: 0 is successful
u32: mem handle for resource

Gets the mem_handle associated with a created dispmanx resource. This can be locked and the memory directly written from the arm to avoid having to copy the image data to GPU.

Get EDID block

Tag:: 0x00030020
Request:: 4 bytes

u32: block number

Response:: 136 bytes

u32: block number
u32: status
u8...: EDID block

This reads the specified EDID block from attached HDMI/DVI device. There will always be at least one block of 128 bytes, but there may be additional blocks. You should keep requesting blocks (starting from 0) until the status returned is non-zero.

FRAME BUFFER TAGS

All tags in the request are processed in one operation.
It is not valid to mix Test tags with Get/Set tags in the same operation and no tags will be returned.
Get tags will be processed after all Set tags.
If an allocate buffer tag is omitted when setting parameters, then no change occurs unless it can be accommodated without changing the buffer base or size.
When an allocate buffer response is returned, the old buffer area (if the base or size has changed) is implicitly freed.

For example:

1.: The current values/defaults are loaded into a temporary struct
2.: The tags are used to overwrite some or all of the values
3.: Validation of Test/Set tags occurs
4.: The Set changes are applied and responses based on the requested Get/Test/Set tags are written to the buffer Duplicating the same tag in one request/response is prohibited. The expected result is either an error or implementation specified undefined behaviour (such as only using the last instance of the tag).

Allocate buffer

Tag:: 0x00040001
Request:: 4 bytes

u32: alignment in bytes

Response:: 8 bytes

u32: frame buffer base address in bytes
u32: frame buffer size in bytes

If the requested alignment is unsupported then the current base and size (which may be 0 if not allocated) is returned and no change occurs.

Release buffer

Tag:: 0x00048001
Request:: 0 bytes
Response:: 0 bytes

Releases and disables the frame buffer.

Blank screen

Tag:: 0x00040002
Request:: 4 bytes

u32: state

Bit 0: 0=off, 1=on
Bits 1-31: reserved for future use (set to 0)

Response:: 4 bytes

u32: state

Bit 0: 0=off, 1=on
Bits 1-31: reserved for future use

Get physical (display) width/height

Tag:: 0x00040003
Request:: 0 bytes
Response:: 8 bytes

u32: width in pixels
u32: height in pixels

Note that the "physical (display)" size is the size of the allocated buffer in memory, not the resolution of the video signal sent to the display device.

Test physical (display) width/height

Tag:: 0x00044003
Request:: 8 bytes

u32: width in pixels
u32: height in pixels

Response:: 8 bytes

u32: width in pixels
u32: height in pixels

Response is the same as the request (or modified), to indicate if this configuration is supported (in combination with all the other settings). Does not modify the current hardware or frame buffer state.

Set physical (display) width/height

Tag:: 0x00048003
Request:: 8 bytes

u32: width in pixels
u32: height in pixels

Response:: 8 bytes

u32: width in pixels
u32: height in pixels

The response may not be the same as the request so it must be checked. May be the previous width/height or 0 for unsupported.

Get virtual (buffer) width/height

Tag:: 0x00040004
Request:: 0 bytes
Response:: 8 bytes

u32: width in pixels
u32: height in pixels

Note that the "virtual (buffer)" size is the portion of buffer that is sent to the display device, not the resolution the buffer itself. This may be smaller than the allocated buffer size in order to implement panning.