Retry Function - Fujitsu MB90335 Series Hardware Manual

CHAPTER 12 USB HOST
12.5 Operation of USB HOST
12.5.6

Retry Function

At the termination of the packet, when NAK or an error such as CRC error occurs, and
the RETRY bit of the host control register 1 (HCNT1) is "1", it continues to retry during a
time period set in the retry timer register (HRTIMER).
■ Retry Function
If an error except STALL and disconnected device happens, it retries to process the token when the
RETRY bit of the host control register 1 (HCNT1). The end condition of retry
"0" setting of RETRY bit of host control register 1(HCNT1)
• Detecting 0 in the retry timer
• Occurrence of an interrupt due to SOF (SOFIRE= 1 of HCNT0 and SOFIRQ= 1 of HIRQ)
• Detection of ACK
• Detection of cutting device
The retry timer is activated when the process of a token is started, counts down with one-bit transfer clock,
and stops counting when a retry happens in an EOF area. The retry timer restarts at the value when the
timer stopped if the SOFIRQ bit of HIRQ was "0". The SOF token was completed, and when the timer
counts down to "0" and a packet ends, any retry request it receives is cancelled and the packet will be
terminated.
Token beginning
When the retry operation is completed, end information on the completed packet is set in related registers.
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Figure 12.5-5 Retry Timer Operation (SOFIRQ of HIRQ = 0)
Token execution
Timer countdown
FUJITSU MICROELECTRONICS LIMITED
EOF SOF
Timer stop
Retry generation
MB90335 Series
retry
Timer restart
CM44-10137-6E