
GR740-UM-DS, Nov 2017, Version 1.7
38
www.cobham.com/gaisler
GR740
4.4
Clock multiplexing for main system clock, SDRAM and SpaceWire
The diagram below shows how the clocks are multiplexed in the design.
Figure 1.
GR740 clock multiplexing
SYSPLL
sys_clkin
pll_locked[1:0]
MEMPLL
mem_extclk
Clock to
SDRAM controller
&
dsu_en
Debug bus and debug unit clocks
Clock Gating
Unit
Gated CPU, FPU
and peripheral clocks
control registers
cpu idle
System clock
SPWPLL
spw_clk
to SPW codec
gr1553_clk
eth0*clk
jtag_tck
to 1553 codec
to GRETH0
to TAP and scan chain
1
0
mem_clksel
mem_clk_in
1
0
1
0
1
0
pll_bypass[0]
pll_bypass[1]
pll_bypass[2]
mem_clk_out
mem_clk_out_diff
1
0
mem_dqm[11]
&
&
&
&
mem_dqm[10]
mem_dqm[7]
mem_ifwidth AND pcimode_enable
mem_ifwidth AND (NOT pcimode_enable)
to PCI core
to GRETH1
to GRETH1
to GRETH1
1
0
Pos clk
Neg clk
mem_dqm[6]
pll_locked[3:2]
pll_locked[5:4]
Clock to
SDRAM devices
external clock split/loop