MB87P2020 Datasheet, PDF (337/356 Pages) Fujitsu Component Limited. – Colour LCD/CRT/TV Controller

Hints and Restrictions
1.7 Robustness of command pipeline against software errors
As described in detail in hardware manual a command should only be written to Lavender/Jasmine when
the flag FLNOM_CWEN is ’1’.
If this rule is followed the command execution of Lavender works correctly but if a command is written
although the FLNOM_CWEN flag is ’0’ the command execution of Lavender may hang (command pipeline
overflow). Only a hardware reset can solve this situation.
In case of a command pipeline overflow the command dataflow via FIFOs is not automatically corrected
but the application can detect a command pipeline overflow with help of the flag FLNOM_EOV and should
perform corrective actions.
Please note that not only wrong written software can cause this problem but also signal distortions on ULB
data bus (ULB_D).
Normally an application polls the FLNOM_CWEN flag so it may be read many times inside a loop. If at
one of these read accesses this flag changes its value from ’0’ to ’1’ due to PCB disturbances the software
stops polling and sends a new command to the graphic controller. Lavender has not finished executing pre-
vious command and a command pipeline overflow occurs.
To avoid this communication problem between MCU and Lavender signal distortions on ULB_D should be
reduced by improving PCB layout as already described in chapter 1.6. Please note that additionally to the
signals described in chapter 1.6 the ULB data bus (ULB_D) is also a critical signal for PCB layout.
The command controller for Jasmine has been redesigned and a command pipeline overflow can not cause
the command execution to hang. But the application has still to take care about the command dataflow syn-
chronization as described above.
Table 1-7 gives an overview and a classification about the described problem.
Table 1-7: Overview for command pipeline robustness
Subject
Description
Classification
Effects without
workaround
Solution/Workaround
Concerned devices
Testcase
Description
If a command is written to Lavender while the flag FLNOM_CWEN is ’0’
the command pipeline may hang. This can be watched with FLNOM_EOV
flag.
Hint
The command controller does not work properly after sending a new com-
mand while FLNOM_CWEN = ’0’. Only a hardware reset can solve this
situation.
For Jasmine no hang-up can occur but the command<-> data synchroniza-
tion can be disturbed.
Write only commands to Lavender when FLNOM_CWEN is ’1’. Keep
special attention to PCB layout for ULB data bus (ULB_D).
MB87J2120 (Lavender)
fixed for MB87P2020 (Jasmine)
fixed for MB87P2020-A (Jasmine redesign)
Every testcase with command execution.
1.8 DMA resistance against wrong settings
In DMA demand mode the DMA controller inside Lavender/Jasmine counts the amount of data words to
be transferred. See hardware manual chapter B-2.1.7 (ULB description) for more details about DMA.
If the amount of data to be transferred in DMA demand mode is equal to ’0’ the Lavender DMA controller
may hang. The data amount of ’0’ can be calculated¹ if:
• IFDMA_LL is set to max. input FIFO size (128 for Lavender) for DMA to input FIFO
Special hints
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