Datasheet

06 February 2012 Broadcom Europe Ltd. 406 Science Park Milton Road Cambridge CB4 0WW Page 197
© 2012 Broadcom Corporation. All rights reserved
Timer Value register:
This register holds the current timer value and is counted down when the counter is running. It is
counted down each timer clock until the value 0 is reached. Then the value register is re-loaded from
the timer load register and the interrupt pending bit is set. The timer count down speed is set by the
timer pre-divide register.
Timer control register:
The standard SP804 timer control register consist of 8 bits but in the BCM implementation there are
more control bits for the extra features. Control bits 0-7 are identical to the SP804 bits, albeit some
functionality of the SP804 is not implemented. All new control bits start from bit 8 upwards.
Differences between a real 804 and the BCM implementation are shown in italics.
Name: Timer control
Address: base + 0x40C
Reset: 0x3E0020
Bit(s)
R/W
Function
31:10
-
<Unused>
23:16
R/W
Free running counter pre
-
scaler. Freq is sys_clk/(prescale+1)
These bits do not exists in a standard 804! Reset value is 0x3E
15:10
-
<Unused>
9
R/W
0 : Free running counter Disabled
1 : Free running counter Enabled
This bit does not exists in a standard 804 timer!
8
R/W
0 : Timers keeps running if ARM is in debug halted mode
1 : Timers halted if ARM is in debug halted mode
This bit does not exists in a standard 804 timer!
7
R/W
0 : Timer disabled
1 : Timer enabled
6
R/W
Not used
, The timer is always in free running mode.
If this bit is set it enables periodic mode in a standard 804. That
mode is not supported in the BC2835M.
5
R/W
0 : Timer interrupt disabled
1 : Timer interrupt enabled
4
R/W
<Not used>
3:2
R/W
Pre
-
scale bits:
00 : pre-scale is clock / 1 (No pre-scale)
01 : pre-scale is clock / 16
10 : pre-scale is clock / 256
11 : pre-scale is clock / 1 (Undefined in 804)
1
R/W
0 : 16
-
bit counters
1 : 23-bit counter
0
R/W
Not used
, The timer is always in wrapping mode.
If this bit is set it enables one-shot mode in real 804. That mode is
not supported in the BCM2835.