Method for autonomously transferring code to a computer without accessing local memory by the central processing unit

• US 5,664,194 A
• Filed: 12/04/1995
• Issued: 09/02/1997
• Est. Priority Date: 12/04/1995
• Status: Expired due to Term

• Current Assignee: Google Inc. (Alphabet Inc.)
• Original Assignee: Metricom, Inc.
• Inventors: Paulsen, David L.
• Primary Examiner(s): Kriess, Kevin A.
• Assistant Examiner(s): CHAVIS, JOHN Q
• Application Number:
  US08/566,877
• Time in Patent Office: 638 Days
• Field of Search: 395/652, 395/712
• US Class Current: 717/178
• CPC Class Codes: G06F 9/4401 Bootstrapping security arrangements therefor G06F21/57

Abstract

In a computer-driven device, a start-up mode after reset is provided whereby boot-up instructions are by default always accepted directly from an external source. The device may comprise a gate array (GA) which is connected directly via a serial port to a receiving or input device, to receive program code for transfer directly as instructions to a microprocessor-type central processing unit. The central processing unit is part of a computer controlled device containing a microprocessor, memory (a RAM), and typically a bulk erase flash memory device, the flash memory device being unprogrammed when the computer controlled device is fabricated originally. When the computer controlled device first powers up, a special mode of operation ensues in which the gate array directly monitor bits received via the serial port from the input device and shifts them into a local register from which bytes or words are loaded directly into the CPU as instructions. A boot sequence is thereby accepted in this manner to load random access memory of the free-running CPU which thereafter can control transfer of additional executable code or load a permanent boot sequence into bulk erase (nonvolatile) flash memory. The invention can be incorporated into a wireless modem/packet terminal node controller. The input device may be a coupling to an external computer system, typically a serial input.

Claims

1. A method for downloading a boot sequence to a computing device having an input element, a gate array, and a CPU, said method in said gate array comprising the steps of:

upon reset looking for instruction requests from the CPU;

accepting at a receiving register digital data from said input element;

checking said register each cycle to determine if said register contains an instruction;

returning a filler instruction to the CPU until said register contains a desired instruction; and

thereupon

transferring content of said register to the CPU as said desired instruction.

2. The method according to claim 1 wherein said input element is a serial input device and wherein said register is a shift register.

3. The method according to claim 1 wherein said register is cleared upon said transferring step for receipt of the next bits to form instructions.

4. The method according to claim 3 wherein a "one" bit is sent via the serial port as a start bit for the beginning of each instruction bit stream.

5. The method according to claim 1 wherein said input element performs parallel data input.

6. The method according to claim 1 wherein a timeout is used to exit from a default state of receiving instructions from an external source.

7. An apparatus for downloading a boot sequence to a computing device, said apparatus comprising:

an input element for receiving digital data from an external source;

a receiving register means coupled to receive said digital data from said input element;

means for checking said register each cycle to determine is said register contains a desired instruction; and

means for repetitively transferring each said valid instruction to said CPU.

8. The apparatus according to claim 7 wherein said input element is a serial input device.

9. The apparatus according to claim 7 wherein said input element is a parallel input device.