GR740-UM-DS, Nov 2017, Version 1.7
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GR740
3.2
Configuration for flight
To achieve the intended radiation tolerance in flight, certain bootstrap signals must be held at a fixed
configuration:
•
DSU_EN must be held low (disabling debug interfaces)
•
JTAG_TRST must be held low (disabling the JTAG TAP)
3.3
Pin multiplexing
The device shares pin between the following groups of interfaces:
•
Part of the PROM/IO interface shares pins with UART 0, UART 1, CAN 0, CAN 1, SpaceWire
debug and MIL-STD-1553B. The pins can also be controlled as general-purpose I/O.
•
The top half of the SDRAM interface shares pins with PCI and Ethernet port 1.
The sections below describes multiplexing for the affected interfaces. Section 30 describes the periph-
eral through which software controls the multiplexing.
3.3.1
PROM/IO interface multiplexing
The selection between the PROM/IO interface and the other low-speed interfaces on the same pins is
done at boot time via the bootstrap signal GPIO[15]. When GPIO[15] is LOW during reset, then the
full PROM/IO interface will be available. When GPIO[15] is HIGH after reset, the alternative func-
tion is routed to the shared pins.
The multiplexing has been designed so that even if starting with all the multiplexed pins set to their
alternative (peripheral) mode, enough dedicated PROM/IO pins are still available to access an 8-bit,
64 KiB boot PROM for bootstrapping the system. Note that it is the top part of the data bus (PRO-
MIO_DATA[15:8]) that is used for the PROM in 8-bit mode.
GPIO[7:6]
Selects SpaceWire router Distributed Interrupt configuration
"00" - Interrupts with acknowledgment mode (32 interrupts with acknowledgments);
"01" - Extended interrupt mode (64 interrupts, no acknowledgments);
"10" - Distributed interrupts disabled, all Dist. Interrupt codes treated as Time-Codes;
"11" - Dist. interrupt disabled, Control code treated as Time-Code if CTRL flags are zero.
GPIO[9:8]
Selects if Ethernet Debug Communication Link 0 (GPIO[8]) and Link 1(GPIO[9]) traffic should
be routed over the Debug AHB bus (HIGH) or the Master I/O AHB bus (LOW).
GPIO[10]
Selects the PROM width. 0: 8-bit PROM, 1: 16-bit PROM
GPIO[11]
Controls the clock gate settings for the SpaceWire router.
GPIO[13:12]
Sets the two least significant bits of the SpaceWire router’s instance ID.
GPIO[14]
Controls reset value of PROM/IO controller’s PROM EDAC enable (PE) bit. When this input is
’1’ at reset, EDAC checking of the PROM area will be enabled.
GPIO[15]
Selects if the PROM/IO interface should be enabled after reset. If this signal is LOW then the
PROM/IO interface is enabled. Otherwise the PROM/IO interface pins are routed to their alter-
native functions.
PLL_BYPASS[2:0]
Bypass PLL and use clock input directly. 2: SpW clock, 1: SDRAM clock, 0: System clock PLL
bypass.
PLL_IGNLOCK
The PLL outputs of the device are gated until the PLL lock outputs have been asserted. Setting
this signal HIGH disables this clock gating for all PLLs, and also removes the lock signals from
the reset generation.
Table 23.
Bootstrap signals
Bootstrap signal
Description