Thread: N900 will not allow USB OTG!
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joerg_rw is offline joerg_rw
2010-05-28 , 11:28
Posts: 2,222 | Thanked: 12,651 times | Joined on Mar 2010 @ SOL 3
#963
Originally Posted by javispedro View Post
To check this was one of the reasons I had started testing with the N810. All of the previous devices (including non id pin in connector ones) use a_host state.
Yes, but aiui this was accomplished by "echo host >mode" triggering a fake ID_GND signal from "PHY" layer to the above machinery, which our 1707 alas is incapable to do.

I studied 2 versions of SPRUF98 for OTG-USB, and found there are actually 3 'correct' ways to put the musb core to hostmode:
* ID pin grounded causing the corresponding flag bit in RXCMD from PHY being asserted, which results in A role for the device and puts musb core into hostmode (for obvious reasons this seems not possible on N900)
* HNP to walk the musb core thru the state transitions involved with host role change (the thing egoshin somewhat accidentally exploited by keeping VBUS alive so session end wasn't detected when swapping the cable, and which might be possible to do by blue_led suggested method, without need of a kickstart PC)
* FORCE_HOSTMODE bit, which - according to
SPRUF98D - October 2009,
"§23.1.4.11 Register to Enable the USB 2.0 Test Modes (TESTMODE)" does:
bit 7 FORCE_HOST:
Set this bit to forcibly put the USB controller into Host mode when SESSION bit is set,
regardless of whether it is connected to any peripheral. The controller remains in Host mode
until the Session bit is cleared, even if a device is disconnected. And if the FORCE_HOST but
remains set, it will re-enter Host mode next time the SESSION bit is set. The operating speed is
determined using the FORCE_HS and FORCE_FS bits.
alas it seems there will be no automatic speed negotiation, no session-end detection and no HOSTDISCON IRQ generated, so the software statemachine found mainly inside function
559 static irqreturn_t musb_stage0_irq()
in musb_core.c which is driven entirely by IRQ triggered by the musb core harware, won't play nice.
Nevertheless we can probably, even definitely, by some patches force the software statemachine into the correct state when sensing a "echo host >mode" is done. Same time we would config the musb core and PHY correctly (set FORCE_HOST bit, enable the DM_PD and DP_PD resistors in PHY for physical hostmode config, etc), and then poll HOSTDISCON from DevCtl register, to detect attachment/removal of a peripheral and his pullup R. We will need a patch in USB protocol driver (I'm wildly guessing here) to do this poll and start chatting with peripheral when due.

description of the FORCE_HOST operation mode
23.1.3.4.6 FORCE_HOST
The Force Host test mode enables the user to instruct the core to operate in Host mode, regardless of
whether it is actually connected to any peripheral i.e. the state of the CID input and the LINESTATE and
HOSTDISCON signals are ignored. (While in this mode, the state of the HOSTDISCON signal can be read
from bit 7 of the DevCtl register.)
This mode, which is selected by setting bit 7 within the Testmode register, allows implementation of the
USB TEST_FORCE_ENABLE (7.1.20). It can also be used for debugging PHY problems in hardware.
While the FORCE_HOST bit remains set, the core will enter Host mode when the Session bit is set and
remain in Host mode until the Session bit is cleared even if a connected device is disconnected during the
session. The operating speed while in this mode is determined for the setting of the FORCE_HS and
FORCE_FS bits of the Testmode register in Section 23.1.4.11.
description of IRQ we will not see in FORCE_HOST mode
HOSTDISCONNECT_RISE
Generate an interrupt event notification when
Hostdisconnect changes from low to high. Applicable only in
host mode (DpPulldown and DmPulldown both set to 1b).
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