
CHAPTER 14 USBU (UNIVERSAL SERIAL BUS UNIT)
User’s Manual U14579EJ2V0UM
328
14.4.12 HCCA format
Table 14-6 shows the HCCA format.
Table 14-6. HCCA Format
Offset
Address
Size
(Bytes)
Field Name
R/W
Function
0
128
HccaInterruptTable
R
Pointer to an InterruptED
0x80
2
HccaFrameNumber
W
Displays the current frame number. This value is updated by the HC
before periodic list processing begins in the frame.
0x82
2
HccaPad1
W
When the HC updates the HccaFrameNumber area, the HC sets
this area to 0.
0x84
4
HccaDoneHead
W
When the HC reaches the end of frame and the decrement value of
the value indicated by the DI area of the TD is 0, the HC writes the
current value of HcDoneHead to this area. If interrupts are enabled,
an interrupt request is generated.
This area will not be written to again by the HC until the WDH bit of
the HcInterruptStatus register is cleared by software. When this area
is zero, an interrupt request is caused by a reason other than an
update of this area, and the HcInterruptStatus register must be
accessed to determine the source of the interrupt request. When this
area is not zero, the interrupt request is a Done queue update
interrupt request. When LSB of this area is not zero, an addition
separate interrupt source has occurred. Therefore, check the
HcInterruptStatus register to determine that source.
0x88
116
reserved
R/W
Reserved for use by the HC.
14.4.13 HCCA overview
The HccaInterruptTable area, which consists of 32 Dword entry tables, points to pointers to each interrupt list of the
ED list. The execution rate is higher for EDs having more linked lists. An ED that exists in only 1 list is executed every
32 ms, and an ED that exists in 2 lists is executed once every 6 ms. When an ED is linked to all 32 lists, it is executed
once for each frame. The last entry of each of the 32 interrupt lists must point to an isochronous list.
After the SOF is sent, the HccaFrameNumber area is rewritten with the value of the FN area of the HcFmNumber
register before the HC reads the ED to be processed in the new frame.