1 .. SPDX-License-Identifier: GPL-2.0
2
3 ==============================================
4 Notes on Oxford Semiconductor PCIe (Tornado) 9
5 ==============================================
6
7 Oxford Semiconductor PCIe (Tornado) 950 serial
8 by a fixed 62.5MHz clock input derived from th
9
10 The baud rate produced by the baud generator i
11 frequency by dividing it by the clock prescale
12 value from 1 to 63.875 in increments of 0.125,
13 divisor is used as with the original 8250, to
14 value from 1 to 65535. Finally a programmable
15 that can take any value from 4 to 16 to divide
16 determine the actual baud rate used. Baud rat
17 to 0.933bps can be obtained this way.
18
19 By default the oversampling rate is set to 16
20 set to 33.875, meaning that the frequency to b
21 for the usual 16-bit divisor is 115313.653, wh
22 frequency of 115200 used by the original 8250
23 used for the divisor to obtain the requested b
24 is unaware of the extra clock controls availab
25
26 The oversampling rate is programmed with the T
27 prescaler is programmed with the CPR/CPR2 regi
28 [OX954]_ [OX958]_. To switch away from the de
29 the prescaler the enhanced mode has to be expl
30 setting bit 4 of the EFR. In that mode settin
31 the prescaler or otherwise it is bypassed as i
32 Additionally writing any value to CPR clears C
33 old software written for older conventional PC
34 devices that do not have the extra prescaler's
35 CPR/CPR2 register pair has to be programmed in
36
37 By using these parameters rates from 15625000b
38 obtained, with either exact or highly-accurate
39 standard and many non-standard rates.
40
41 Here are the figures for the standard and some
42 (including those quoted in Oxford Semiconducto
43 the requested rate (r), the actual rate yielde
44 from the requested rate (d), and the values of
45 (tcr), the clock prescaler (cpr) and the divis
46 new ``get_divisor`` handler:
47
48 ::
49
50 r: 15625000, a: 15625000.00, d: 0.0000%, tcr
51 r: 12500000, a: 12500000.00, d: 0.0000%, tcr
52 r: 10416666, a: 10416666.67, d: 0.0000%, tcr
53 r: 8928571, a: 8928571.43, d: 0.0000%, tcr
54 r: 7812500, a: 7812500.00, d: 0.0000%, tcr
55 r: 4000000, a: 4000000.00, d: 0.0000%, tcr
56 r: 3686400, a: 3676470.59, d: -0.2694%, tcr
57 r: 3500000, a: 3496503.50, d: -0.0999%, tcr
58 r: 3000000, a: 2976190.48, d: -0.7937%, tcr
59 r: 2500000, a: 2500000.00, d: 0.0000%, tcr
60 r: 2000000, a: 2000000.00, d: 0.0000%, tcr
61 r: 1843200, a: 1838235.29, d: -0.2694%, tcr
62 r: 1500000, a: 1492537.31, d: -0.4975%, tcr
63 r: 1152000, a: 1152073.73, d: 0.0064%, tcr
64 r: 921600, a: 919117.65, d: -0.2694%, tcr
65 r: 576000, a: 576036.87, d: 0.0064%, tcr
66 r: 460800, a: 460829.49, d: 0.0064%, tcr
67 r: 230400, a: 230414.75, d: 0.0064%, tcr
68 r: 115200, a: 115207.37, d: 0.0064%, tcr
69 r: 57600, a: 57603.69, d: 0.0064%, tcr
70 r: 38400, a: 38402.46, d: 0.0064%, tcr
71 r: 19200, a: 19201.23, d: 0.0064%, tcr
72 r: 9600, a: 9600.06, d: 0.0006%, tcr
73 r: 4800, a: 4799.98, d: -0.0004%, tcr
74 r: 2400, a: 2400.02, d: 0.0008%, tcr
75 r: 1200, a: 1200.00, d: 0.0000%, tcr
76 r: 300, a: 300.00, d: 0.0000%, tcr
77 r: 200, a: 200.00, d: 0.0000%, tcr
78 r: 150, a: 150.00, d: 0.0000%, tcr
79 r: 134, a: 134.00, d: 0.0000%, tcr
80 r: 110, a: 110.00, d: 0.0000%, tcr
81 r: 75, a: 75.00, d: 0.0000%, tcr
82 r: 50, a: 50.00, d: 0.0000%, tcr
83 r: 25, a: 25.00, d: 0.0000%, tcr
84 r: 4, a: 4.00, d: 0.0000%, tcr
85 r: 2, a: 2.00, d: 0.0000%, tcr
86 r: 1, a: 1.00, d: 0.0000%, tcr
87
88 With the baud base set to 15625000 and the uns
89 limitation imposed by ``serial8250_get_baud_ra
90 below 300bps become unavailable in the regular
91 200bps requires the baud base to be divided by
92 the unsigned 16-bit range. The historic spd_c
93 used by encoding the values for, the prescaler
94 and the clock divisor (DLM/DLL) as follows to
95 required:
96
97 ::
98
99 31 29 28 20 19 16 15
100 +-----+-----------------+-------+------------
101 |0 0 0| CPR2:CPR | TCR |
102 +-----+-----------------+-------+------------
103
104 Use a value such encoded for the ``custom_divi
105 ASYNC_SPD_CUST flag set in the ``flags`` field
106 passed with the TIOCSSERIAL ioctl(2), such as
107 utility and its ``divisor`` and ``spd_cust`` p
108 the baud rate of 38400bps. Note that the valu
109 oversampling rate to 16 and prescaler values b
110 clamped by the driver to 1.
111
112 For example the value of 0x1f4004e2 will set C
113 respectively to 0x1f4, 0x0 and 0x04e2, choosin
114 the oversampling rate and the clock divisor of
115 respectively. These parameters will set the b
116 port to 62500000 / 62.500 / 1250 / 16 = 50bps.
117
118 Maciej W. Rozycki <macro@orcam.me.uk>
119
120 .. [OX200] "OXPCIe200 PCI Express Multi-Port B
121 Inc., DS-0045, 10 Nov 2008, Section "950 Mo
122
123 .. [OX952] "OXPCIe952 PCI Express Bridge to Du
124 Oxford Semiconductor, Inc., DS-0046, Mar 06
125 p. 20
126
127 .. [OX954] "OXPCIe954 PCI Express Bridge to Qu
128 Semiconductor, Inc., DS-0047, Feb 08, Secti
129
130 .. [OX958] "OXPCIe958 PCI Express Bridge to Oc
131 Semiconductor, Inc., DS-0048, Feb 08, Secti
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.