JTAG Mailbox (JMB) System
64
SLAU367P – October 2012 – Revised April 2020
Copyright © 2012–2020, Texas Instruments Incorporated
System Resets, Interrupts, and Operating Modes, System Control Module
(SYS)
1.12.1 JMB Configuration
The JMB supports two transfer modes: 16-bit and 32-bit. Setting JMBMODE enables 32-bit transfer mode.
Clearing JMBMODE enables 16-bit transfer mode.
1.12.2 JMBOUT0 and JMBOUT1 Outgoing Mailbox
Two 16-bit registers are available for outgoing messages to the JTAG port. JMBOUT0 is only used when
using 16-bit transfer mode (JMBMODE = 0). JMBOUT1 is used in addition to JMBOUT0 when using 32-bit
transfer mode (JMBMODE = 1). When the application wishes to send a message to the JTAG port, it
writes data to JMBOUT0 for 16-bit mode, or JMBOUT0 and JMBOUT1 for 32-bit mode.
JMBOUT0FG and JMBOUT1FG are read only flags that indicate the status of JMBOUT0 and JMBOUT1,
respectively. When JMBOUT0FG is set, JMBOUT0 has been read by the JTAG port and is ready to
receive new data. When JMBOUT0FG is reset, the JMBOUT0 is not ready to receive new data.
JMBOUT1FG behaves similarly.
1.12.3 JMBIN0 and JMBIN1 Incoming Mailbox
Two 16-bit registers are available for incoming messages from the JTAG port. Only JMBIN0 is used when
in 16-bit transfer mode (JMBMODE = 0). JMBIN1 is used in addition to JMBIN0 when using 32-bit transfer
mode (JMBMODE = 1). When the JTAG port wishes to send a message to the application, it writes data
to JMBIN0 for 16-bit mode, or JMBIN0 and JMBIN1 for 32-bit mode.
JMBIN0FG and JMBIN1FG are flags that indicate the status of JMBIN0 and JMBIN1, respectively. When
JMBIN0FG is set, JMBIN0 has data that is available for reading. When JMBIN0FG is reset, no new data is
available in JMBIN0. JMBIN1FG behaves similarly.
JMBIN0FG and JMBIN1FG can be configured to clear automatically by clearing JMBCLR0OFF and
JMBCLR1OFF, respectively. Otherwise, these flags must be cleared by software.
1.12.4 JMB NMI Usage
The JMB handshake mechanism can be configured to use interrupts to avoid unnecessary polling if
desired. In 16-bit mode, JMBOUTIFG is set when JMBOUT0 has been read by the JTAG port and is
ready to receive data. In 32-bit mode, JMBOUTIFG is set when both JMBOUT0 and JMBOUT1 has been
read by the JTAG port and are ready to receive data. If JMBOUTIE is set, these events cause a system
NMI. In 16-bit mode, JMBOUTIFG is cleared automatically when data is written to JMBOUT0. In 32-bit
mode, JMBOUTIFG Is cleared automatically when data is written to both JMBOUT0 and JMBOUT1. In
addition, the JMBOUTIFG can be cleared when reading SYSSNIV. Clearing JMBOUTIE disables the NMI
interrupt.
In 16-bit mode, JMBINIFG is set when JMBIN0 is available for reading. In 32-bit mode, JMBINIFG is set
when both JMBIN0 and JMBIN1 are available for reading. If JMBOUTIE is set, these events cause a
system NMI. In 16-bit mode, JMBINIFG is cleared automatically when JMBIN0 is read. In 32-bit mode,
JMBINIFG Is cleared automatically when both JMBIN0 and JMBIN1 are read. In addition, the JMBINIFG
can be cleared when reading SYSSNIV. Clearing JMBINIE disables the NMI interrupt.
1.13 JTAG and SBW Lock Mechanism Using the Electronic Fuse
A device can be protected from unauthorized access by restricting accessibility of JTAG commands that
can be transferred to the device by the JTAG and SBW interface. This is achieved by programming the
electronic fuse. When the device is protected, the JTAG and SBW interface still remains functional, but
JTAG commands that give direct access into the device are completely disabled. There are two ways to
lock the device. Both of these require the programming of two signatures that reside in FRAM. JTAG
Signature 1 (memory location 0FF80h) and JTAG Signature 2 (memory location 0FF82h) control the
behavior of the device locking mechanism.
NOTE:
When a device has been protected, Texas Instruments cannot access the device for a
customer return. Access is only possible if a BSL is provided with its corresponding key or an
unlock mechanism is provided by the customer.