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chipset: more on different HCI variants, spellcheck

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In this chapter, we first explain how Bluetooth chipsets are connected physically and
then provide information about popular Bluetooth chipset and their use with BTstack.
In this chapter, we first explain how Bluetooth chipsets are connected physically and then provide information about popular Bluetooth chipset and their use with BTstack.
The communication between a Host (a computer or an MCU) and a Host Controller (the actual Bluetoot chipset) follows the Host Controller Interface (HCI), see {@fig:HostChipsetConnection}. HCI defines how commands, events, asynchronous and synchronous data packets are exchanged. Asynchronous packets (ACL) are used for data transfer, while synchronous packets (SCO) are used for Voice with the Headset and the Hands-Free Profiles.
## HCI Interface
The communication between a Host (a computer or an MCU) and a Host Controller (the actual Bluetooth chipset) follows the Host Controller Interface (HCI), see {@fig:HostChipsetConnection}. HCI defines how commands, events, asynchronous and synchronous data packets are exchanged. Asynchronous packets (ACL) are used for data transfer, while synchronous packets (SCO) are used for Voice with the Headset and the Hands-Free Profiles.
![Host Controller to Host connection](../doc/manual/docs/picts/host_chipset_connection.png){#fig:HostChipsetConnection}
On desktop-class computers incl. laptops, USB is mainly used as HCI transport layer. For USB Bluetooth chipsets, there is little variation: most USB dongles on the market currently contain a Broadcom BCM20702 or a CSR 851x chipset.
On embedded systems, UART connections are used instead, although USB could be used as well.
### HCI H2
On desktop-class computers incl. laptops, USB is mainly used as HCI transport layer. For USB Bluetooth chipsets, there is little variation: most USB dongles on the market currently contain a Broadcom BCM20702 or a CSR 851x chipset. It is also called H2.
Most USB Bluetooth dongles on the market conatin either an Broadcom BCM20702
On embedded systems, UART connections are used instead, although USB could be used as well.
For UART connections, different transport layer variants exist. The most common one is the official "UART Transport", also called H4. It requires hardware flow control via the CTS/RTS lines and assumes no errors on the UART lines. The "Three-Wire UART Transport", also called H5, makes use of the SLIP protocol to transmit a packet and can deal with packet loss and bit-errors by retransmission. Finally, Texas Instruments created the "eHCILL transport" layer based on H4 that allows both sides to enter sleep mode without loosing synchronisation.
For UART connections, different transport layer variants exist.
### HCI H4
The most common one is the official "UART Transport", also called H4. It requires hardware flow control via the CTS/RTS lines and assumes no errors on the UART lines.
### HCI H5
The "Three-Wire UART Transport", also called H5, makes use of the SLIP protocol to transmit a packet and can deal with packet loss and bit-errors by retransmission. While it is possible to use H5 really with "three wires" without hardware handshake, we recommend to use a full UART with hardware handshake. If your design lacks the hardware handshake, H5 is your only option.
### eHCILL
Finally, Texas Instruments extended H4 to create the "eHCILL transport" layer that allows both sides to enter sleep mode without loosing synchronisation. While it is easier to implement than H5, it it is only supported by TI chipsets and cannot handle packet loss or bit-errors.
### HCI Shortcomings
Unfortunately, the HCI standard misses a few relevant details:
* For UART based connections, the initial baud rate isn't defined but most Bluetooth chipsets use 115200 baud. For better throughput, a higher baud rate is necessary, but there's no standard HCI command to change it. Instead, each vendor had to come up with their own set of vendor-specific commands. Sometimes, additional steps, e.g. doing a warm reset, are neceesary to activate the baud rate change as well.
* For UART based connections, the initial baud rate isn't defined but most Bluetooth chipsets use 115200 baud. For better throughput, a higher baud rate is necessary, but there's no standard HCI command to change it. Instead, each vendor had to come up with their own set of vendor-specific commands. Sometimes, additional steps, e.g. doing a warm reset, are necessary to activate the baud rate change as well.
* Some Bluetooth chipsets don't have a unique MAC address. On start, the MAC address needs to be set, but there's no standard HCI command to set it.
* SCO data for Voice can either be transmitted via the HCI interface or via an explicit PCM/I2S interface on the chipset. Most chipsets default to the PCM/I2S interface. To use it via USB or for Wide-Band Speech in the Hands-Free Profile, the data needs to be delivered to the host MCU. Newer Bluetooth standards define a HCI command to configure the SCO routing, but it is not implemented in the chipsets we've tested so far. Instead, this is configured in a vendor-specific way as well.
* In addition, most vendors allow to patch or configure their chipsets at run time by sending custom comands to the chipset. Obviously, this is also vendor dependent.
* SCO data for Voice can either be transmitted via the HCI interface or via an explicit PCM/I2S interface on the chipset. Most chipsets default to the PCM/I2S interface. To use it via USB or for Wide-Band Speech in the Hands-Free Profile, the data needs to be delivered to the host MCU. Newer Bluetooth standards define a HCI command to configure the SCO routing, but it is not implemented in the chipsets we've tested so far. Instead, this is configured in a vendor-specific way as well.
* In addition, most vendors allow to patch or configure their chipsets at run time by sending custom commands to the chipset. Obviously, this is also vendor dependent.
## Documentation and Support
The level of developer documentation and support varies widely between the various Bluetooth chipset providers.
From our experience, only Texas Instruments and EM Microelectronics provide all relevant information directly on their website. Nordic Semiconductor does not officially have Bluetooth chipsets with HCI interface, but their the documentation on their nRF5 series is complete and very informative. TI and Nordic also provide excellent support via their respective web forum.
@ -31,11 +43,13 @@ Broadcom, whose Bluetooth + Wifi division has been acquired by the Cypress Semic
CSR, which has been acquired by Qualcomm, provides all relevant information on their Support website after signing an NDA.
Chipset | Type | HCI Transport | BD_ADDR (1) | SCO over HCI (2) | LE DLE | Multiple LE Roles | BTstack folder | Comment
## Chipset Overview
Chipset | Type | HCI Transport | BD_ADDR (1) | SCO over HCI (2) | LE DLE | Multiple LE Roles | BTstack folder | Comment
-------------------- |-----------| ---------------|--------------|------------------|--------|----------------------|----------------|---------
Broadcom UART | Dual mode | H4, H5 | rarely | Probably (2) | No | Maybe (3) | bcm | Max UART baudrate 2 mbps
Broadcom USB Dongles | Dual mode | USB | Yes | Yes | No | No | bcm |
CSR UART | Dual mode | H4, H5 | rarely | No (didn't work) | No | No | csr |
Broadcom USB Dongles | Dual mode | USB | Yes | Yes | No | No | bcm |
CSR UART | Dual mode | H4, H5 | rarely | No (didn't work) | No | No | csr |
CSR USB Dongles | Dual mode | USB | Mostly | Yes | No | No | csr |
Dialog DA14581 | LE | H4, SPI | ? | n.a. | No | No | | Waiting for dev kit
EM 9301 | LE | SPI | No | n.a. | No | No | em9301 | Custom HCI SPI implementation
@ -49,25 +63,25 @@ TI CC256x, WL183x | Dual mode | H4, H5, eHCILL | Yes | Yes
1. BD_ADDR: Not all Bluetooth chipset come with a fixed valid MAC Address. Better Broadcom and CSR dongles come with a MAC address from the dongle manufacturer, but cheaper ones might come with identical addresses.
2. SCO over HCI: All Bluetooth Classic chipsets support SCO over HCI, for those that are marked with No, we either didn't try or didn't found enough information to configure it correctly.
3. Multiple LE Roles: Apple uses Broadcom Bluetooth+Wifi in their iOS devices and newer iOS versions support multipe concurrent LE roles,
3. Multiple LE Roles: Apple uses Broadcom Bluetooth+Wifi in their iOS devices and newer iOS versions support multiple concurrent LE roles,
so at least some Broadcom models support multiple concurrent LE roles.
## Broadcom
Before the Broadcom Wifi+Bluetooth division was taken over by Cypress Semiconductor, it was not possible to buy Broadcom chipset in low quantities. Nevertheless, module manufacturers like Ampak created modules that contained Broadcom BCM chipsets (Bluetooth as well as Bluetooth+Wifi combos) that might already have been pre-tested for FCC and similar certifications.
A popular example is the Ampak AP6212A module that contains an BCM 43438A1 and is used on the Raspberry Pi 3, the RedBear Duo, and the RedBear IoT pHAT for older Rasperry Pi models.
A popular example is the Ampak AP6212A module that contains an BCM 43438A1 and is used on the Raspberry Pi 3, the RedBear Duo, and the RedBear IoT pHAT for older Raspberry Pi models.
The best source for documentation on vendor specific commands so far has been the source code for blueZ and the Bluedroid Bluetooth stack from Android.
Broadcom USB dongles do not require special configuration, however SCO data is not routed over USB by default.
**Init scripts**: For UART connected chipsets, an init script has to be uploaded after power on. For Bluetooth chipsets that are used in Broadcom Wifi+Bluetooth combos, this file often can be found as a binary file in Linux distributions with the ending *'.hcd'* or as part of the WICED SDK as C source file that contains the init script as a data array for use without a file system.
**Init scripts**: For UART connected chipsets, an init script has to be uploaded after power on. For Bluetooth chipsets that are used in Broadcom Wifi+Bluetooth combos, this file often can be found as a binary file in Linux distributions with the ending *'.hcd'* or as part of the WICED SDK as C source file that contains the init script as a data array for use without a file system.
To find the correct file, Broadcom chipsets return their model number when asked for their local name.
BTstack supports uploading of the init script in two variants: using .hcd files looked up by name in the posix-h4 port and by linking against the init script in the WICED port. While the init script is processed, the chipsets RTS line goes high, but only 2 ms after the command complete event for the last command from the init script was sent. BTstack waits for 10 ms after receiving the command complete event for the last command to avoid sending before RTS goes high and the command fails.
**BD Addr** can be set with a custom command. A fixed addres is provided on some modules, e.g. the AP6212A, but not on others.
**BD Addr** can be set with a custom command. A fixed address is provided on some modules, e.g. the AP6212A, but not on others.
**SCO data** can be configured with a custom command found in the bluez sources. It works with USB chipsets. The chipsets don't implement the SCO Flow Control that is used by BTstack for UART connected devices. A forum suggests to send SCO packets as fast as they are received since both directions have the same constant speed.
@ -79,15 +93,15 @@ SCO Data can be routed over HCI for both USB dongles and UART connections, howev
## CSR
Similar to Broadcom, the best source for documentation is the source code for blueZ.
Similar to Broadcom, the best source for documentation is the source code for blueZ.
CSR USB dongles do not require special configuration and SCO data is routed over USB by default.
CSR chipset do not require an actual init script in general, but they allow to configure the chipset via so-called PSKEYs. After setting one or more PSKEYs, a warm reset activates the new setting.
**BD Addr** can be set via PSKEY. A fixed address can be provided if the chipset has some kind of persistent memory to store it. Most USB Bluetooth dongles have a fixed BD ADDR.
**BD Addr** can be set via PSKEY. A fixed address can be provided if the chipset has some kind of persistent memory to store it. Most USB Bluetooth dongles have a fixed BD ADDR.
**SCO data** can be configured via a set of PSKEYs. We haven't been able to route SCO data over HCI for UART connections yet.
**SCO data** can be configured via a set of PSKEYs. We haven't been able to route SCO data over HCI for UART connections yet.
**Baud rate** can be set as part of the initial configuration and gets actived by the warm reset.
@ -100,13 +114,13 @@ SCO Data is routed over HCI for USB dongles, but not for UART connections. HSP a
Dialog Semiconductor offers the DA14581, an LE-only SoC that can be programmed with an HCI firmware. The HCI firmware can be uploaded on boot into SRAM or stored in the OTP (One-time programmable) memory, or in an external SPI.
We just ordered a Dev Kit and will try to implement the firmware upload to SRAM option. This chipset supports the Bluetooth 4.2. specification but does not seem to implement the Data Length Extension nor supports multiple concurrent roles.
We just ordered a Dev Kit and will try to implement the firmware upload to SRAM option. This chipset supports the Bluetooth 4.2. specification but does not seem to implement the Data Length Extension nor supports multiple concurrent roles.
## EM Microelectronic Marin
For a long time, the EM9301 has been the only Bluetooth Single-Mode LE chipset with an HCI interface. The EM9301 can be connected via SPI or UART. The UART interface does not support hardware flow control and is not recommended for use with BTstack. The SPI mode uses a proprietary but documented exension to implement flow control and signal if the EM9301 has data to send.
For a long time, the EM9301 has been the only Bluetooth Single-Mode LE chipset with an HCI interface. The EM9301 can be connected via SPI or UART. The UART interface does not support hardware flow control and is not recommended for use with BTstack. The SPI mode uses a proprietary but documented extension to implement flow control and signal if the EM9301 has data to send.
**Update:** EM has just announced a new EM9304 that also features an HCI mode and supports the Bluetooth 4.2. specification. It seems to support the Data Length Extension but not and multiple concurrent roles.
**Update:** EM has just announced a new EM9304 that also features an HCI mode and supports the Bluetooth 4.2. specification. It seems to support the Data Length Extension but not and multiple concurrent roles.
**BD Addr** must be set during startup since it does not have a stored fix address.
@ -114,7 +128,7 @@ For a long time, the EM9301 has been the only Bluetooth Single-Mode LE chipset w
**Baud rate** could be set for UART mode. For SPI, the master controls the speed via the SPI Clock line.
**Init scripts** are not required although it is possible to upload small firmware patches.
**Init scripts** are not required although it is possible to upload small firmware patches.
**BTstack integration**: The common code for the EM9301 is provided by *btstack_chipset_em9301.c*. During the setup, *btstack_chipset_em9301_instance* function is used to get a *btstack_chipset_t* instance and passed to *hci_init* function. It enables to set the BD Addr during start.
@ -123,17 +137,17 @@ For a long time, the EM9301 has been the only Bluetooth Single-Mode LE chipset w
The Single-Mode LE chipsets from the Nordic nRF5 series chipsets do not have an HCI interface. Instead, they provide an LE Bluetooth Stack as a binary library, the so-called *SoftDevices*. Developer can write their Bluetooth application on top of this library usually. Since the chipset can be programmed, it can also be loaded with a firmware that provides a regular HCI H4 interface for a Host.
An interesting feature of the nRF5 chipsets is that they can support multiple LE roles at the same time, e.g. being Central in one connection and a Peripheral in another connection. Also, the nRF52 SoftDevice implementation supports the Bluetooth 4.2 Data Length Extension.
An interesting feature of the nRF5 chipsets is that they can support multiple LE roles at the same time, e.g. being Central in one connection and a Peripheral in another connection. Also, the nRF52 SoftDevice implementation supports the Bluetooth 4.2 Data Length Extension.
Both nRF5 series, the nRF51 and the nRF52, can be used with an HCI firmware. The HCI firmware does not support the Data Length Extension yet, but this will be supported soon. Also, the nRF51 does not support encryted connections at the moment (November 18th, 2016) although this might become supported as well.
Both nRF5 series, the nRF51 and the nRF52, can be used with an HCI firmware. The HCI firmware does not support the Data Length Extension yet, but this will be supported soon. Also, the nRF51 does not support encrypted connections at the moment (November 18th, 2016) although this might become supported as well.
**BD ADDR** is not set automatically. However, during production, a 64-bit random number is stored in the each chip. Nordic uses this random number as a random static address in their SoftDevice implementation.
**BD ADDR** is not set automatically. However, during production, a 64-bit random number is stored in the each chip. Nordic uses this random number as a random static address in their SoftDevice implementation.
**SCO data** is not supported since it is LE only.
**Baud rate** is fixed to 115200 by the patch althouth the firmware could be extended to support a baud rate change.
**Baud rate** is fixed to 115200 by the patch although the firmware could be extended to support a baud rate change.
**Init script** is not required.
**Init script** is not required.
**BTstack integration**: No special chipset driver is provided. In order to use the random static address, the provided patch stores this address as the (invalid) public address that is returned by the HCI Read BD Addr command. When BTstack detects that it is a Nordic chipset, it automatically uses this address as random static address - unless the app chooses to use private addresses.
@ -164,13 +178,13 @@ To use these chipsets with BTstack, you need to install an arm-none-eabi gcc too
STMicroelectronics offers the Bluetooth V2.1 + EDR chipset STLC2500D that supports SPI and UART H4 connection.
**BD Addr** can be set with custom command alhough all chipsets have an official address stored.
**BD Addr** can be set with custom command although all chipsets have an official address stored.
**SCO data** might work. We didn't try.
**Baud rate** can be set with custom command. The baud rate change of the chipset happens within 0.5 seconds. At least on BTstack, knowning exactly when the command was fully sent over the UART is non-trivial, so BTstack switches to the new baud rate after 100 ms to expect the command response on the new speed.
**Init scripts** are not required although it is possible to upload firmware patches.
**Init scripts** are not required although it is possible to upload firmware patches.
**BTstack integration**: Support for the STLC2500C is provided by *btstack_chipset_stlc.c*. During the setup, *btstack_chipset_stlc2500d_instance* function is used to get a *btstack_chipset_t* instance and passed to *hci_init* function. It enables higher UART baud rate and to set the BD Addr during startup.
@ -178,7 +192,7 @@ STMicroelectronics offers the Bluetooth V2.1 + EDR chipset STLC2500D that suppor
## Texas Instruments CC256x series
The Texas Instruments CC256x series is currently in its fourth iteration and provides a Classic-only (CC2560), a Dual-mode (CC2564), and a Classic + ANT (CC2567) model. A variant of the Dual-mode chipset is also integrated into TI's WiLink 8 Wifi+Bluetooth combo modules of the WL183x, WL185x, WL187x, and WL189x series.
The Texas Instruments CC256x series is currently in its fourth iteration and provides a Classic-only (CC2560), a Dual-mode (CC2564), and a Classic + ANT (CC2567) model. A variant of the Dual-mode chipset is also integrated into TI's WiLink 8 Wifi+Bluetooth combo modules of the WL183x, WL185x, WL187x, and WL189x series.
The CC256x chipset is connected via an UART connection and supports the H4, H5 (since third iteration), and eHCILL.
@ -204,7 +218,7 @@ CC256xC | 0x9a1a | 6.12.26
The Makefile at *chipset/cc256x/Makefile.inc* is able to automatically download and convert the requested file. It does this by:
- Downloading one or more [BTS files](http://processors.wiki.ti.com/index.php/CC256x_Downloads) for your chipset.
- Running the Python script:
- Running the Python script:
<!-- -->
@ -218,7 +232,7 @@ SCO Data can be routed over HCI, so HFP Wide-Band Speech is supported.
The Toshiba TC35661 Dual-Mode chipset is available in three variants: standalone incl. binary Bluetooth stack, as a module with embedded stack or with a regular HCI interface. The HCI variant has the model number TC35661–007.
We've tried their USB Evaluation Stick that contains an USB-to-UART adapter and the PAN1026 module that contains the TC35661 -501. We have been told by our distributor that the -501 variant also supports the HCI interface. However, while our tests have shown that Classic Bluetooth with SPP works fine with this variant, none of the LE commands work.
We've tried their USB Evaluation Stick that contains an USB-to-UART adapter and the PAN1026 module that contains the TC35661 -501. We have been told by our distributor that the -501 variant also supports the HCI interface. However, while our tests have shown that Classic Bluetooth with SPP works fine with this variant, none of the LE commands work.
**SCO data** might work. We didn't try.