Host control
GPIO27
DSP control
GPIO26
1 2 3 4 65
Parallel_Boot
No
Yes
Initialize GP I/O MUX
and Dir registers
GPIO[15:0] = input
GPIO27 = input
GPIO26=output
Read KeyValue to
determine DataSize
Valid
KeyValue
(0x08AA or
0x10AA)
?
reserved words
Read and discard 8
Read EntryPoint
address
CopyData
Call
Return
EntryPoint
Return
FLASH_ENTRY_POINT
Enable pullups on
GPIO[15:0], GPIO26,
and GPIO27
and assign appropriate
GetWordData function
Parallel_Boot Function (GPIO)
Figure 2-14. Parallel GPIO bootloader Handshake Protocol
1. The DSP indicates it is ready to start receiving data by pulling the GPIO26 pin low.
2. The bootloader waits until the host puts data on GPIO[15:0]. The host signals to the DSP that data is
ready by pulling the GPIO27 pin low.
3. The DSP reads the data and signals the host that the read is complete by pulling GPIO26 high.
4. The bootloader waits until the host acknowledges the DSP by pulling GPIO27 high.
5. The DSP again indicates it is ready for more data by pulling the GPIO26 pin low.
This process is repeated for each data value to be sent.
Figure 2-15 shows an overview of the Parallel GPIO bootloader flow.
Figure 2-15. Parallel GPIO Mode Overview
Figure 2-16 shows the transfer flow from the host side. The operating speed of the CPU and host are not
critical in this mode as the host will wait for the DSP and the DSP will in turn wait for the host. In this
manner the protocol will work with both a host running faster and a host running slower then the DSP.
36 Bootloader Features SPRU722C – November 2004 – Revised October 2006
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