FreeCalypso > hg > freecalypso-docs

annotate Calypso-digital-voice @ 23:14391ad53281

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
FCDEV3B-repackaging article removed for legal reasons The idea expressed in that article, namely the idea that some party other than Mother Mychaela could be permitted to create a derived work based on FCDEV3B board design and have it be accepted into the FreeCalypso family, is no longer allowed by our current stance on the matters of intellectual property, particularly Falconia IP. For technical content, the new FC-modem-family and Quadband-ideas articles should fully supplant this old FCDEV3B-repackaging article.
author Mychaela Falconia <falcon@freecalypso.org>
date Wed, 23 Oct 2019 00:43:21 +0000
parents 9baf6215285b
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
10
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
1 Digital voice on FreeCalypso modems via MCSI
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
2 ============================================
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
3
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
4 The Calypso chip provides a little-used auxiliary synchronous serial interface
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
5 called MCSI. It is an auxiliary interface to the DSP part of the Calypso
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
6 (controlled solely by the DSP and not directly accessible to the ARM part); it
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
7 is not clear what other uses TI may have had in mind for this interface, but
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
8 one advertised feature of TI's TCS211 chipset+firmware solution is Bluetooth
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
9 support in the form of using MCSI as a digital voice channel to be connected to
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
10 TI's Bluetooth Island chip. In FreeCalypso we are not interested in Bluetooth
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
11 per se, but we are interested in getting a digital voice channel out of our
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
12 modem for GSM voice calls in order to compete with the mainstream proprietary
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
13 GSM modem modules which do provide such digital voice channels.
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
14
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
15 Our current development board (FCDEV3B) has MCSI brought out on a header for
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
16 experimentation, and as of 2019-03 we finally got this MCSI working as a proper
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
17 digital voice interface.
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
18
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
19 Hardware interface
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
20 ==================
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
21
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
22 MCSI consists of 4 hardware signals:
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
23
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
24 * MCSI_CLK is the bit clock output from the Calypso; in pure hardware terms
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
25 this signal is bidirectional, but unless you are going to develop your own
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
26 DSP code patches, its direction is determined by the DSP ROM code, which
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
27 configures MCSI_CLK as an output, i.e., the Calypso acts as the clock master.
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
28
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
29 * MCSI_FSYNCH is the frame sync output from the Calypso; it is the same deal as
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
30 with MCSI_CLK: bidirectional in pure hardware terms, but if you are not
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
31 changing the DSP code with your own custom patches, it is an output from the
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
32 Calypso.
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
33
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
34 * MCSI_RXD is the voice uplink bits input to the Calypso: the user's application
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
35 processor needs to feed voice uplink bits to this pin as timed by MCSI_CLK
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
36 and MCSI_FSYNCH.
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
37
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
38 * MCSI_TXD is the voice downlink output from the Calypso: as the vocoder in the
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
39 Calypso DSP decodes received downlink speech from GSM codecs into linear PCM,
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
40 this PCM voice downlink is put out on this MCSI_TXD pin, in synchrony with
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
41 MCSI_CLK and MCSI_FSYNCH.
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
42
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
43 The format in which digital voice samples are exchanged via MCSI between the
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
44 Calypso and the user's application processor is 16-bit linear PCM, 8000 samples
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
45 per second, thus requiring 128 kbps of bandwidth. The synchronous serial
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
46 interface details are as follows:
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
47
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
48 * When MCSI is enabled, the Calypso puts out a 520 kHz clock on MCSI_CLK,
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
49 produced by dividing the 13 MHz master clock by 25. This clock as put out by
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
50 the Calypso has a perfect 50% duty cycle.
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
51
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
52 * Given that a new pair of samples (uplink and downlink) needs to be transferred
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
53 once every 125 us (1/8000th of a second, for 8000 samples per second), this
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
54 520 kHz bit clock is further divided by 65 to produce an 8 kHz clock on
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
55 MCSI_FSYNCH, i.e., every 65 bits there is a frame synchronization pulse on
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
56 MCSI_FSYNCH. The width of this frame sync pulse is one full bit time, the
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
57 pulse is active high, and the MCSI_FSYNCH line stays low the rest of the time.
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
58
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
59 * Calypso outputs MCSI_FSYNCH and MCSI_TXD are updated on the rising edge of
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
60 MCSI_CLK and should be sampled on the falling edge of the same clock by the
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
61 user's application processor. The MCSI_RXD input is sampled on the falling
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
62 edge of MCSI_CLK by the Calypso, and should be updated on the rising edge of
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
63 the same clock by the user's application processor.
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
64
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
65 * Each voice sample (both uplink and downlink) is transferred from the most
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
66 significant bit to the least significant bit (MSB first), starting with the
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
67 clock cycle immediately following the frame sync cycle, i.e., the cycle in
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
68 which MCSI_FSYNCH is asserted by the Calypso.
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
69
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
70 * Given that each frame is 65 bits long (520 kHz bit clock divided by 8 kHz
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
71 frame rate) and that 16 bit slots out of every frame are used to transfer
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
72 voice sample bits, plus one bit slot for frame sync, it follows that 48 bit
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
73 slots out of every frame are dummies. The Calypso puts out 0 bits on MCSI_TXD
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
74 in all bit slots that don't carry voice sample bits.
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
75
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
76 A graphical depiction of what I just described verbally can be found on page
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
77 3074 of this TI OMAP document:
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
78
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
79 ftp://ftp.freecalypso.org/pub/ARM/OMAP/sprugn4r.pdf
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
80
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
81 Calypso MCSI corresponds to what this OMAP document calls "Mode 1", i.e.,
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
82 Figure 21-14 at the top of the page, NOT the other one below it.
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
83
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
84 Enabling and disabling MCSI for digital voice
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
85 =============================================
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
86
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
87 TI's DSP ROM code supports two modes of operation in which MCSI is activated,
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
88 called "Bluetooth cordless" and "Bluetooth headset". In the "BT cordless" mode
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
89 the voice path is connected between the chipset's native analog voice hw and
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
90 MCSI, with GSM out of the picture; in the "BT headset" mode the voice path is
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
91 connected between the GSM vocoder and MCSI, with the local analog voice hw out
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
92 of the picture. The latter "BT headset" mode is the only one which we currently
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
93 support in FreeCalypso; the "BT cordless" mode does not work properly as of this
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
94 writing - the step of enabling the Voice Band Codec block in the Iota ABB for
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
95 this mode is currently missing. Proper support for the "BT cordless" mode can
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
96 be added if a real need for it ever arises, but it would take some work, and
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
97 right now there is no business case for it.
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
98
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
99 In TI's TCS211 firmware architecture (see TCS211-fw-arch document) entry into
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
100 and exit from these "Bluetooth" MCSI voice routing modes is handled via the
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
101 RiViera Audio Service fw component, specifically its Audio Mode facility,
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
102 usually via the audio_full_access_write() API call. When asked to switch voice
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
103 routing modes, this RV Audio Service component sends an MMI_AUDIO_MODE_REQ
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
104 message to L1, the L1A component passes the request to L1S, and L1S finally
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
105 twiddles the magic control bits in the DSP API RAM.
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
106
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
107 In FreeCalypso we currently provide two ways for the end user to enter the
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
108 "BT headset" mode for digital access to GSM voice:
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
109
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
110 * The original way is the AT@VPATH=n command, which provides "raw" access to
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
111 the RV Audio Service's voice routing mode switch call. Setting AT@VPATH=2
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
112 enters the "BT headset" mode, AT@VPATH=0 returns to the normal "GSM only"
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
113 mode (MCSI disabled), and AT@VPATH=1 enters the currently not-working
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
114 "BT cordless" mode.
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
115
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
116 * The new way is the session-long AT@VSEL=n boolean setting. In the default
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
117 AT@VSEL=0 mode the firmware functions like before (MCSI disabled, voice calls
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
118 go to the analog voice hw), but if your application needs the digital voice
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
119 interface instead of analog, you can set AT@VSEL=1 once at the beginning of
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
120 your modem session. In this AT@VSEL=1 mode, whenever a GSM voice call is
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
121 connected (dialed or answered), the MCSI clocks are switched on (MCSI_CLK and
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
122 MCSI_FSYNCH outputs come to life) and the "BT headset" voice routing mode is
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
123 entered at the appropriate point in the call establishment process; when the
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
124 call disconnects (either side hangs up), MCSI is turned off. The new logic
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
125 internally performs the equivalent of AT@VPATH=2 and AT@VPATH=0 at appropriate
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
126 times.
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
127
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
128 Why does one need our new AT@VSEL=1 logic for dynamic switching into and out of
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
129 MCSI "BT headset" mode, why not simply set AT@VPATH=2 upfront and run with it?
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
130 Two reasons:
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
131
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
132 1) If MCSI is enabled continuously and not just when needed during voice calls,
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
133 the DSP never goes quiescent during idle periods, and the Calypso is not
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
134 allowed to enter deep sleep. Both of these factors are detrimental to proper
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
135 power management - the whole idea is that when a GSM modem is idle (not in a
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
136 call, but listening to paging and ready to accept incoming calls), most of
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
137 the hw needs to be powered down as much as possible, to reduce power
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
138 consumption to a minimum and prolong standby battery life.
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
139
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
140 2) There is a bug in the DSP code (present in the ROM and not corrected by the
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
141 patches we are using) that manifests if MCSI is already running when the very
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
142 first voice call after system boot is connected. Our AT@VSEL=1 mechanism
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
143 reliably avoids this DSP bug (ensured by the timing sequence of when we turn
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
144 on the vocoder and when we turn on MCSI), and it is my (Mother Mychaela's)
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
145 guess that TI probably missed this DSP bug because their own Bluetooth
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
146 handling code most likely worked very similarly to my AT@VSEL=1
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
147 implementation.
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
148
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
149 Thus the short story is that if you are using the digital voice interface via
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
150 MCSI, just set AT@VSEL=1 at the beginning of your modem session, and whatever
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
151 hardware you connect to MCSI needs to be OK with the clocks (MCSI_CLK and
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
152 MCSI_FSYNCH) appearing only during active voice calls, and being off at other
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
153 times.
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
154
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
155 It should also be noted that the new AT@VSEL=1 mechanism is implemented properly
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
156 only in our new hybrid firmwares, i.e., Magnetite hybrid and Selenite. The
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
157 legacy configs (l1reconst etc) using the blob version of G23M PS and ACI from
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
158 Openmoko (maintained only for regression testing and debugging purposes) also
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
159 implement the AT@VSEL command, but the AT@VSEL=1 mode will work somewhat
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
160 erratically in that version: the modem may enable MCSI at the wrong time, and
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
161 it will sometimes fail to turn it off at the end of a call. The implementation
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
162 of this functionality resides entirely in the "high-level audio driver" module
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
163 in ACI, this module is different between TCS2 and TCS3 versions of ACI, and
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
164 there is no justification for expending the effort to make the new feature work
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
165 in the old version of ACI: it is an entirely new feature added in FreeCalypso,
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
166 not present in any old Calypso modems, hybrid fw is the way forward in FC, thus
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
167 we only need to support new features in our hybrid firmwares.
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
168
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
169 The alternative approach of tapping VSP
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
170 =======================================
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
171
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
172 MCSI is not the only digital voice interface in the Calypso chipset: there is
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
173 also another interface called VSP (Voice Serial Port), which is a private
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
174 interface between Calypso and Iota chips. Because it was always intended to be
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
175 a private interface internal to the core chipset, not an external application
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
176 interface like MCSI, none of the standard Calypso-based phone or modem board
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
177 designs expose it in any accessible way - instead it goes from one BGA to the
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
178 other on inner PCB layers with zero accessibility for probing. Our FCDEV3B is
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
179 no exception in this regard, as our modem core is based on a commercial modem
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
180 design from a decade before our time.
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
181
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
182 Because it took us a very long time to get MCSI working as a practically usable
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
183 digital voice interface (the new AT@VSEL=1 mechanism is the key, without this
12
9baf6215285b Calypso-digital-voice: typo fix
Mychaela Falconia <falcon@freecalypso.org>
parents: 10
diff changeset
184 firmware piece MCSI is not practically usable), much thought has been given
10
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
185 earlier to the alternative idea of tapping into VSP. There are two
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
186 possibilities with that one:
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
187
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
188 1) Given that Calypso VSP is a clock slave (it expects the ABB chip to provide
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
189 the clock and frame sync signals), those who desire their digital voice i/f
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
190 to be a PCM slave (not a PCM master like TI's "BT headset" function over
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
191 MCSI) will likely be very tempted to disconnect Calypso VSP from the Iota
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
192 chip entirely and to connect it to their own application instead. However,
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
193 in the absence of source code for the DSP ROM this approach would be
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
194 incredibly risky (if the DSP is not too happy with the non-Calypso-sourced
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
195 timing you feed to the VSP, how are you going to debug it deep within the
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
196 DSP black box?), and I (Mother Mychaela) consider it so risky that if anyone
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
197 wants to do it, you will be entirely on your own - don't expect any help
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
198 from me.
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
199
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
200 2) A much safer approach would be to keep the VSP clock and frame sync
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
201 connections between Calypso and Iota chips, but also make them available
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
202 externally, i.e., have your application logic sync itself to these clocks.
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
203 Voice downlink could then be received just by passively tapping VSP lines,
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
204 and sending your own voice uplink via VSP would require cutting only the one
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
205 line that carries voice uplink bits from Iota to Calypso. It would then
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
206 effectively be just like MCSI (a PCM master to the user's application), but
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
207 without requiring any support in the firmware, instead being completely
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
208 invisible to the Calypso firmware and to the DSP.
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
209
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
210 However, because we don't have any board on which VSP signals are accessible to
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
211 probing, there are several unknowns with this interface:
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
212
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
213 * Is the VSP clock produced by the Iota chip 500 kHz (13 MHz master clock
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
214 divided by 26) or 520 kHz (same master clock divided by 25)? The available
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
215 Iota datasheet says 500 kHz, but if that is correct, how is the frame sync
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
216 handled? 500 kHz does not divide evenly by 8 kHz. Does Iota's clock + frame
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
217 sync output alternate between 62-bit and 63-bit frames, producing an 8 kHz
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
218 frame rate on average? Sounds messy and convoluted...
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
219
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
220 * It is not clear at all exactly when Iota's VSP clocks are started and stopped,
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
221 and whether the bit clock runs continuously during an active call (like
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
222 MCSI_CLK does), or if it is gated on only for those bit slots that carry
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
223 actual voice sample bits.
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
224
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
225 If we are going to produce a new FreeCalypso modem based on our current FCDEV3B,
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
226 but repackaged into some end use form factor, as things stand today (2019-03),
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
227 we are going to use MCSI rather than VSP for the digital voice interface. While
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
228 MCSI has definitely been a huge hassle and requires the user to issue one extra
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
229 setup command (AT@VSEL=1) at the beginning of each modem session, at least it
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
230 is now a known beast, and a known-working one. Committing to VSP in a
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
231 commercial product design without ever having seen these VSP signals on an
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
232 oscilloscope would be very irresponsible; if someone really wishes to go with
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
233 VSP instead of MCSI, the responsible approach would be to first design and build
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
234 another development board with VSP signals brought out for experimentation, and
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
235 only then possibly use it in a commercial product design after it becomes a
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
236 known beast.
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
237
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
238 From the standpoint of pure curiosity, I would be very interested in a
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
239 development board with VSP access, just to answer the above questions and fill
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
240 that gap in my Calypso knowledge. But switching to a more practical hat,
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
241 spending some 10 to 15 kUSD just to satisfy that curiosity would be very
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
242 difficult to justify - thus there is a very strong chance that VSP will never
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
243 be explored, Which is not really a problem at all, as for a practically usable
17003ecbb9fc Calypso-digital-voice article written,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
244 external digital voice channel we now have working MCSI.