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Implement the BLE handshaking

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The BLE communication sends a handshake packet containing a passphrase
based on the serial number of the device. Sadly, we can't actually read
the serial number from the device until after this handshake has
successfully completed, which makes it a bit of a chicken-and-egg
problem from a communication standpoint. However, the serial number is
also exposed in the bluetooth device name the device advertizes, which
is the reason for the newly added DC_IOCTL_BLE_GET_NAME ioctl.

Thanks to Janice McLaughlin for pointing out the logic of this magic
handshake.

Based-on-code-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Jef Driesen 2019-02-05 14:05:49 +01:00
parent 6ba0726a42
commit 4baf140d25
1 changed files with 69 additions and 0 deletions
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69
src/oceanic_atom2.c
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@ -22,6 +22,8 @@
#include <string.h> // memcpy
#include <stdlib.h> // malloc, free
#include <libdivecomputer/ble.h>
#include "oceanic_atom2.h"
#include "oceanic_common.h"
#include "context-private.h"
@ -46,6 +48,7 @@
#define CMD_INIT 0xA8
#define CMD_VERSION 0x84
#define CMD_HANDSHAKE 0xE5
#define CMD_READ1 0xB1
#define CMD_READ8 0xB4
#define CMD_READ16 0xB8
@ -766,6 +769,65 @@ oceanic_atom2_transfer (oceanic_atom2_device_t *device, const unsigned char comm
return DC_STATUS_SUCCESS;
}
/*
* The BLE communication sends a handshake packet that seems
* to be a passphrase based on the BLE name of the device
* (more specifically the serial number encoded in the name).
*
* The packet format is:
* 0xe5
* < 8 bytes of passphrase >
* one-byte checksum of the passphrase.
*/
static dc_status_t
oceanic_atom2_ble_handshake(oceanic_atom2_device_t *device)
{
dc_status_t rc = DC_STATUS_SUCCESS;
dc_device_t *abstract = (dc_device_t *) device;
// Retrieve the bluetooth device name.
// The format of the name is something like 'FQ001124', where the
// two first letters are the ASCII representation of the model
// number (e.g. 'FQ' or 0x4651 for the i770R), and the six digits
// are the serial number.
char name[8 + 1] = {0};
rc = dc_iostream_ioctl (device->iostream, DC_IOCTL_BLE_GET_NAME, name, sizeof(name));
if (rc != DC_STATUS_SUCCESS) {
if (rc == DC_STATUS_UNSUPPORTED) {
// Allow skipping the handshake if no name. But the download
// will likely fail.
WARNING (abstract->context, "Bluetooth device name unavailable.");
return DC_STATUS_SUCCESS;
} else {
return rc;
}
}
// Force a null terminated string.
name[sizeof(name) - 1] = 0;
// Check the minimum length.
if (strlen (name) < 8) {
ERROR (abstract->context, "Bluetooth device name too short.");
return DC_STATUS_IO;
}
// Turn ASCII numbers into just raw byte values.
unsigned char handshake[10] = {CMD_HANDSHAKE};
for (unsigned int i = 0; i < 6; i++) {
handshake[i + 1] = name[i + 2] - '0';
}
// Add simple checksum.
handshake[9] = checksum_add_uint8 (handshake + 1, 8, 0x00);
// Send the command to the dive computer.
rc = oceanic_atom2_transfer (device, handshake, sizeof(handshake), ACK, NULL, 0, 0);
if (rc != DC_STATUS_SUCCESS)
return rc;
return DC_STATUS_SUCCESS;
}
dc_status_t
oceanic_atom2_device_open (dc_device_t **out, dc_context_t *context, dc_iostream_t *iostream, unsigned int model)
@ -857,6 +919,13 @@ oceanic_atom2_device_open (dc_device_t **out, dc_context_t *context, dc_iostream
goto error_free;
}
if (dc_iostream_get_transport (device->iostream) == DC_TRANSPORT_BLE) {
status = oceanic_atom2_ble_handshake(device);
if (status != DC_STATUS_SUCCESS) {
goto error_free;
}
}
// Override the base class values.
if (OCEANIC_COMMON_MATCH (device->base.version, aeris_f10_version)) {
device->base.layout = &aeris_f10_layout;