Difference between revisions of "Unit BCM2708"

Revision as of 04:22, 17 October 2016

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Description

This unit provides the BCM2708 specific implementations of the following devices:

• SPI0
• I2C0
• I2C1
• SPI1
• SPI2
• I2C Slave
• SPI Slave
• DMA
• PWM0
• PWM1
• PCM
• GPIO
• UART0
• UART1
• SDHCI (eMMC)

• Clock
• ARM Timer
• Random
• Mailbox
• Watchdog
• Framebuffer

• MIPI CSI-2 (Camera Serial Interface)
• DSI (Display Serial Interface)

BCM2708 SPI0 Device

The BCM2708 has a single master mode SPI controller that supports 3 wire, 2 wire and LoSSI modes of operation. It also has 2 auxiliary SPI masters which do not support DMA mode (see SPI1/2 below).

The main SPI0 controller supports polled, interrupt and DMA modes and includes 3 chip selects although only CS0 and 1 are available on the 26 or 40 pin header.

By default SPI0 can appear on GPIO pins 7 to 11 (CS1, CS0, MISO, MOSI, SCLK) using alternate function 0 or on GPIO pins 35 to 39 (CS1, CS0, MISO, MOSI, SCLK) using alternate function 0, only pins 7 to 11 are available on the header.

BCM2708 I2C0/1 Device

The BCM2708 has 3 Broadcom Serial Controller (BSC) devices which are fast mode (400Kz) masters numbered BSC0, BSC1 and BSC2.

Device BSC2 is dedicated to the HDMI interface and is not availale for use by the ARM processor. All BSC devices contain a 16 byte FIFO, support 7 bit and 10 bit addressing and have software configurable clock timing.

By default BSC0 can appear on GPIO pins 0 and 1 (Alternate function 0), 28 and 29 (Alternate function 0) or 44 and 45 (Alternate function 1). Unfortunately on all except the Revision 1 models none of these pins are available on the 26 or 40 pin header.

Note: On the Raspberry Pi A+/B+/Zero/2B/3B the ID EEPROM pins on the 40 pin header are actually connected to GPIO 0 and 1 (BSC0)

Device BSC1 can appear on GPIO pins 2 and 3 (Alternate function 0) or 44 and 45 (Alternate function 2) but only pins 2 and 3 are exposed on the 26 or 40 pin header.

BCM2708 SPI1/2 Device

The BCM2708 has 2 additional SPI universal masters available as part of the AUX device which support interrupt mode but not DMA and therefore only allow limited bandwidth transfers due to the CPU overhead required to sustain high data rates.

Both devices support 3 chip selects, by default SPI1 is available on GPIO pins 16 to 21 (CS2, CS1, CS0, MISO, MOSI, SCLK) using alternate function 4 and SPI2 is available on GPIO pins 40 to 45 (MISO, MOSI, SCLK, CS0, CS1, CS2) using alternate function 4. Only pins 16 to 21 are available on the header and only on the 40 pin header of the Raspberry Pi A+/B+/Zero/2B/3B.

BCM2708 DMA Device

The DMA controller has 16 channels in total although not all are available for software to use as some are already used by the GPU.

The firmware will pass the value dma.dmachans on the command line which will indicate which channels are available for our use.

Channels 0 to 6 are normal channels which support 2D stride and transfers up to 1GB per control block

Channels 7 to 14 are Lite channels which do not support stride and only allow transfers up to 64KB per control block Channel 15 is not mentioned in most documentation and is shown as not available in the mask passed in dma.dmachans

Channel 0 and 15 are Bulk channels which have an additional FIFO for faster transfers (8 beat burst per read)

BCM2708 PWM0/1 Device

The BCM2708 has a single PWM controller with 2 independent output bit streams with multiple algorithms for generating the output pulse. The PWM controller supports either a single data register (independent per channel) or a 16 x 32 FIFO which also supports DMA mode transmission.

On the Raspberry Pi PWM0 and PWM1 are also connected via GPIO pins 40 and 45 (40 and 41 on the Raspberry Pi 3B) to the audio circuit and allow playback of digital audio signals via the 3 or 4 pole line jack (depending on model).

PWM0 is available on GPIO pins 12 (function 0), 18 (function 5), 40 (function 0) and 52 (function 1). PWM1 is available on GPIO pins 13 (function 0), 19 (function 5), 41, 45 (function 0) and 53 (function 1).

On the Raspberry Pi A and B only pin 18 is exposed on the 26 pin header. On the Raspberry Pi A+/B+/Zero/2B/3B pins 12, 18 and 19 are exposed on the 40 pin header.

BCM2708 GPIO Device

The GPIO has 54 pins available each with multiple alternate functions. All pins can be configured as input or output and all can have pull up or down applied.

Not all pins are exposed on the 26 or 40 pin header of the Raspberry Pi, for details of which pins are available see:

Raspberry Pi A and B - https://www.raspberrypi.org/documentation/usage/gpio/README.md

Raspberry Pi A+/B+/2B/3B/Zero - https://www.raspberrypi.org/documentation/usage/gpio-plus-and-raspi2/README.md

Some of the 54 pins are used for peripheral communication (such as the SD card) and are not available for general use,take care when changing function selects on pins to avoid disabling certain system peripherals.

Event detection can be enabled for both high and low levels as well as rising and falling edges, there is also an asynchronous rising or falling edge detection which can detect edges of very short duration.

BCM2708 UART0 Device

The UART0 device is an ARM PL011 UART which supports programmable baud rates, start, stop and parity bits and hardware flow control and many others. The UART0 is similar to the industry standard 16C650 but with a number of differences, the PL011 has a some optional features such as IrDA, Serial InfraRed and DMA which are not supported by the Broadcom implementation. In the standard configuration the UART0 TX and RX lines are connected to GPIO pins 14 and 15 respectively (Alternate function 0) but they can be remapped via GPIO function selects to a number of other locations. On the Raspberry Pi (all models) none of these alternate pin mappings are exposed via the 26 or 40 pin header and therefore cannot be used easily. This means that UART0 and UART1 cannot be used at the same time.

On the Raspberry Pi 3B the UART0 can be mapped to GPIO pins 32 and 33 (Alternate function 3) to communicate with the built in Bluetooth module.

BCM2708 UART1 Device

The UART1 device is a Broadcom implementation that is part of the AUX device which also includes the SPI1 and SPI2 devices. This device is termed a Mini UART and has a smaller feature set than the PL011 UART but still supports a fairly standard communication protocol with programmable baud rate and hardware flow control.

The Mini UART is similar to the standard 16550 device but is missing some of the features, the device also has no DMA support so high speed transfers will produce a higher CPU load. In the standard configuration the UART1 TX and RX lines are connected to GPIO pins 14 and 15 respectively (Alternate function 5) but they can be remapped via GPIO function selects to a number of other locations. On the Raspberry Pi (all models) none of these alternate pin mappings are exposed via the 26 or 40 pin header and therefore cannot be used easily. This means that UART0 and UART1 cannot be used at the same time.

On the Raspberry Pi 3B the UART1 can be mapped to GPIO pins 32 and 33 (Alternate function 5) to communicate with the built in Bluetooth module.

BCM2708 SDHCI Device

The SDHCI controller on the BCM2708 is an Arasan SD Host controller.

The Card Detect pin is connected to GPIO pin 47 (on the RPi Model A/B)(Not connected on the RPi Model A+/B+)

The Write Protect pin is not connected on any RPi model.

Constants

To be documented

Type definitions

To be documented

Public variables

To be documented

Function declarations

To be documented

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