chipset: more on different HCI variants, spellcheck

chipset/README.md

@@ -1,28 +1,40 @@
-In this chapter, we first explain how Bluetooth chipsets are connected physically and 
+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.
-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. 
+### 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.
+
 On embedded systems, UART connections are used instead, although USB could be used as well.
 
-Most USB Bluetooth dongles on the market conatin either an Broadcom BCM20702 
+For UART connections, different transport layer variants exist.
 
-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.
+### 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. 
+  * 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.
@@ -31,6 +43,8 @@ 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 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
@@ -49,13 +63,13 @@ 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.
 
@@ -67,7 +81,7 @@ To find the correct file, Broadcom chipsets return their model number when asked
 
 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.
 
@@ -104,7 +118,7 @@ We just ordered a Dev Kit and will try to implement the firmware upload to SRAM
 
 ## 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.
 
@@ -125,13 +139,13 @@ The Single-Mode LE chipsets from the Nordic nRF5 series chipsets do not have an
 
 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.
 
 **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.
 
@@ -164,7 +178,7 @@ 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.