79 lines
2.6 KiB
Text
79 lines
2.6 KiB
Text
TDA19988 Driver (HDMI Framer)
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=============================
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Overview
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--------
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This is the driver for the HDMI Framer chip commonly found on the BeagleBone
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Black.
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Interface
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---------
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To make things easy for the frame buffer driver, a block device driver
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interface is provided. Read requests cause the TDA19988 driver to read
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the EDID and return the data.
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Documentation
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-------------
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The documentation available is rather thin. NXP doesn't provide a
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datasheet on their website and they did not respond to my request
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for a datasheet. There are a few other sources of information:
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* TDA9983B.pdf - this chip is similar but not the same. Full
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register descriptions are provided. This was suggested to me by
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the author of the Linux driver and someone at BeagleBoard.org as
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neither of them were able to get a full datasheet for the TDA19988.
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* TDA19988.pdf - you can probably find this on the net. It's a
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pre-production draft of the datasheet for the TDA19988. It has
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some information about how things work, but it doesn't give details
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on the registers.
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* LPC4350_FPU_TFT_HDMI-v2.0/Driver/tda19988.c - there's some
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example code from NXP for a Hitex LPC4350 REV A5 which includes
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a BSD licensed driver from NXP. It isn't complete as it only does
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test mode, put-through mode, and EDID reading. Some of the comments
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in the code make it seem like it isn't totally working/tested.
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* linux/drivers/gpu/drm/i2c/tda998x_drv.c - there is a Linux driver
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which implements a lot of functionality. As is always the case,
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great care has to be taken to only study the code to learn the
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functionality of the chip and not reproduce/copy the code.
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Limitations
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-----------
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Currently, only the EDID reading functionality is implemented.
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Testing the Code
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----------------
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Starting up an instance:
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/bin/service up /usr/sbin/tda19988 -label tda19988.1.3470 \
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-args 'cec_bus=1 cec_address=0x34 hdmi_bus=1 hdmi_address=0x70'
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Killing an instance:
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/bin/service down tda19988.1.3470
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The driver is meant to be accessed from other drivers using the block
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device protocol, so it doesn't have a reserved major number and device file.
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However, if you want a simple test from user space, you can create a temporary
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device file to read the EDID like this:
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cd /dev
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mknod tda19988 b 32 0
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chmod 600 tda19988
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/bin/service up /usr/sbin/tda19988 -label tda19988.1.3470 \
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-dev /dev/tda19988 \
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-args 'cec_bus=1 cec_address=0x34 hdmi_bus=1 hdmi_address=0x70'
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dd if=/dev/tda19988 of=/root/edid.dat count=1 bs=128
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/bin/service down tda19988.1.3470
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hexdump -C /root/edid.dat
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rm tda19988
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The hexdump should begin with the EDID magic number: 00 ff ff ff ff ff ff 00
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