ST STM32G0 1 Series Reference Manual page 1297

RM0444
Bits 13:12 STATRX[1:0]: Status bits, for reception transfers
– Device mode
– Host mode
Universal serial bus full-speed host/device interface (USB)
These bits contain information about the endpoint status, which are listed in
Reception status encoding on page
their value. When the application software writes 0, the value remains unchanged, while
writing 1 makes the bit value to toggle. Hardware sets the STATRX bits to NAK when a
correct transfer has occurred (VTRX = 1) corresponding to a OUT or SETUP (control only)
transaction addressed to this endpoint, so the software has the time to elaborate the
received data before it acknowledges a new transaction.
Double-buffered bulk endpoints implement a special transaction flow control, which control
the status based upon buffer availability condition (Refer to
endpoints and usage in Device
If the endpoint is defined as isochronous, its status can be only "VALID" or "DISABLED", so
that the hardware cannot change the status of the endpoint after a successful transaction. If
the software sets the STATRX bits to 'STALL' or 'NAK' for an isochronous endpoint, the USB
peripheral behavior is not defined. These bits are read/write but they can be only toggled by
writing 1.
These bits are the host application controls to start, retry, or abort host transactions driven
by the channel.
These bits also contain information about the device answer to the last IN channel
transaction and report the current status of the channel according to the following STATRX
table of states:
- DISABLE
DISABLE value is reported in case of ACK acknowledge is received on a single-buffer
channel. When in DISABLE state the channel is unused or not active waiting for application
to restart it by writing VALID. Application can reset a VALID channel to DISABLE to abort a
transaction. In this case the transaction is immediately removed from the host execution
list. If the aborted transaction was already under execution it is regularly terminated on the
USB but the relative VTRX interrupt is not generated.
- VALID
A host channel is actively trying to submit USB transaction to device only when in VALID
state.VALID state can be set by software or automatically by hardware on a NAKED
channel at the start of a new frame. When set to VALID, an host channel enters the host
execution queue and waits permission from the host frame scheduler to submit its
configured transaction.
VALID value is also reported in case of ACK acknowledge is received on a double-buffered
channel. In this case the channel remains active on the alternate buffer while application
needs to read the current buffer and toggle DTOGTX. In case software is late in reading
and the alternate buffer is not ready, the host channel is automatically suspended
transparently to the application. The suspended double buffered channel is re-activated as
soon as delay is recovered and DTOGTX is toggled.
- NAK
NAK value is reported in case of NAK acknowledge received. When in NAK state the
channel is suspended and does not try to transmit. NAK state is moved to VALID by
hardware at the start of the next frame, or software can change it to immediately retry
transmission by writing it to VALID, or can disable it and abort the transaction by writing
DISABLE
- STALL
STALL value is reported in case of STALL acknowledge received. When in STALL state the
channel behaves as disabled. Application should not retry transmission but reset the USB
and re-enumerate.
1300. These bits can be toggled by software to initialize
mode).
RM0444 Rev 5
Table 224:
Section 37.5.3: Double-buffered
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